Performance Improvements in .NET Core 3.0

Stephen

May 15th, 2019

Back when we were getting ready to ship .NET Core 2.0, I wrote a blog post exploring some of the many performance improvements that had gone into it. I enjoyed putting it together so much and received such a positive response to the post that I did it again for .NET Core 2.1, a version for which performance was also a significant focus. With //build last week and .NET Core 3.0‘s release now on the horizon, I’m thrilled to have an opportunity to do it again. .NET Core 3.0 has a ton to offer, from Windows Forms and WPF, to single-file executables, to async enumerables, to platform intrinsics, to HTTP/2, to fast JSON reading and writing, to assembly unloadability, to enhanced cryptography, and on and on and on… there is a wealth of new functionality to get excited about. For me, however, performance is the primary feature that makes me excited to go to work in the morning, and there’s a staggering amount of performance goodness in .NET Core 3.0. In this post, we’ll take a tour through some of the many improvements, big and small, that have gone into the .NET Core runtime and core libraries in order to make your apps and services leaner and faster.

Setup

Benchmark.NET has become the preeminent tool for doing benchmarking of .NET libraries, and so as I did in my 2.1 post, I’ll use Benchmark.NET to demonstrate the improvements. Throughout the post, I’ll include the individual snippets of benchmarks that highlight the particular improvement being discussed. To be able to execute those benchmarks, you can use the following setup: 1. Ensure you have .NET Core 3.0 installed, as well as .NET Core 2.1 for comparison purposes. 2. Create a directory named BlogPostBenchmarks . 3. In that directory, run dotnet new console . 4. Replace the contents of BlogPostBenchmarks.csproj with the following:

<Project Sdk="Microsoft.NET.Sdk"> <PropertyGroup> <OutputType>Exe</OutputType> <AllowUnsafeBlocks>true</AllowUnsafeBlocks> <TargetFrameworks>netcoreapp2.1;netcoreapp3.0</TargetFrameworks> </PropertyGroup> <ItemGroup> <PackageReference Include="BenchmarkDotNet" Version="0.11.5" /> <PackageReference Include="System.Drawing.Common" Version="4.5.0" /> <PackageReference Include="System.IO.Pipelines" Version="4.5.0" /> <PackageReference Include="System.Threading.Channels" Version="4.5.0" /> </ItemGroup> </Project>

Replace the contents of Program.cs with the following:

using BenchmarkDotNet.Attributes; using BenchmarkDotNet.Configs; using BenchmarkDotNet.Jobs; using BenchmarkDotNet.Running; using BenchmarkDotNet.Toolchains.CsProj; using Microsoft.Win32.SafeHandles; using System; using System.Buffers; using System.Collections; using System.Collections.Concurrent; using System.Collections.Generic; using System.Collections.Immutable; using System.Diagnostics; using System.Drawing; using System.Drawing.Drawing2D; using System.Globalization; using System.IO; using System.IO.Compression; using System.IO.Pipelines; using System.Linq; using System.Net; using System.Net.Http; using System.Net.NetworkInformation; using System.Net.Security; using System.Net.Sockets; using System.Runtime.CompilerServices; using System.Runtime.InteropServices; using System.Security.Authentication; using System.Security.Cryptography.X509Certificates; using System.Text; using System.Text.RegularExpressions; using System.Threading; using System.Threading.Channels; using System.Threading.Tasks; using System.Xml; [MemoryDiagnoser] public class Program { static void Main(string[] args) => BenchmarkSwitcher.FromTypes(new[] { typeof(Program) }).Run(args); // ... paste benchmark code here }

To execute a particular benchmark, unless otherwise noted, copy and paste the relevant code to replace the

// ... above, and execute dotnet run -c Release -f netcoreapp2.1 --runtimes netcoreapp2.1 netcoreapp3.0 --filter "*Program*" . This will compile and run the tests in release builds, on both .NET Core 2.1 and .NET Core 3.0, and print out the results for comparison in a table.

Caveats A few caveats before we get started:

Any discussion involving microbenchmark results deserves a caveat that measurements can and do vary from machine to machine. I’ve tried to pick stable examples to share (and have run these tests on multiple machines in multiple configurations to help validate that), but don’t be too surprised if your numbers differ from the ones I’ve shown; hopefully, however, the magnitude of the improvements demonstrated carries through. All of the shown results are from a nightly Preview 6 build for .NET Core 3.0. Here’s my configuration, as summarized by Benchmark.NET, on my Windows configuration and on my Linux configuration:

BenchmarkDotNet=v0.11.5, OS=Windows 10.0.17763.437 (1809/October2018Update/Redstone5) Intel Core i7-7660U CPU 2.50GHz (Kaby Lake), 1 CPU, 4 logical and 2 physical cores .NET Core SDK=3.0.100-preview6-011854 [Host] : .NET Core 2.1.9 (CoreCLR 4.6.27414.06, CoreFX 4.6.27415.01), 64bit RyuJIT Job-RODBZD : .NET Core 2.1.9 (CoreCLR 4.6.27414.06, CoreFX 4.6.27415.01), 64bit RyuJIT Job-TVOWAH : .NET Core 3.0.0-preview6-27712-03 (CoreCLR 3.0.19.26071, CoreFX 4.700.19.26005), 64bit RyuJIT BenchmarkDotNet=v0.11.5, OS=ubuntu 18.04 Intel Xeon CPU E5-2673 v4 2.30GHz, 1 CPU, 4 logical and 2 physical cores .NET Core SDK=3.0.100-preview6-011877 [Host] : .NET Core 2.1.10 (CoreCLR 4.6.27514.02, CoreFX 4.6.27514.02), 64bit RyuJIT Job-SSHMNT : .NET Core 2.1.10 (CoreCLR 4.6.27514.02, CoreFX 4.6.27514.02), 64bit RyuJIT Job-CHXNFO : .NET Core 3.0.0-preview6-27713-12 (CoreCLR 3.0.19.26071, CoreFX 4.700.19.26307), 64bit RyuJIT

Unless otherwise mentioned, benchmarks were executed on Windows. In many cases, performance is equivalent between Windows and Unix, but in others, there can be non-trivial discrepancies between them, in particular in places where .NET relies on OS functionality, and the OS itself has different performance characteristics. I mentioned posts on .NET Core 2.0 and .NET Core 2.1, but I didn’t mention .NET Core 2.2. .NET Core 2.2 was primarily focused on ASP.NET, and while there were terrific performance improvements at the ASP.NET layer in 2.2, the release was primarily focused on servicing for the runtime and core libraries, with most improvements post-2.1 skipping 2.2 and going into 3.0. With that out of the way, let’s have some fun.

Span and Friends

One of the more notable features introduced in .NET Core 2.1 was Span<T> , along with its friends ReadOnlySpan<T> , Memory<T> , and ReadOnlyMemory<T> . The introduction of these new types came with hundreds of new methods for interacting with them, some on new types and some with overloaded functionality on existing types, as well as optimizations in the just-in-time compiler (JIT) for making working with them very efficient. The release also included some internal usage of Span<T> to make existing operations leaner and faster while still enjoying maintainable and safe code. In .NET Core 3.0, much additional work has gone into further improving all such aspects of these types: making the runtime better at generating code for them, increasing the use of them internally to help improve many other operations, and improving the various library utilities that interact with them to make consumption of these operations faster. To work with a span, one first needs to get a span, and several PRs have made doing so faster. In particular, passing around a Memory<T> and then getting a Span<T> from it is a very common way of creating a span; this is, for example, how the various Stream.WriteAsync and ReadAsync methods work, accepting a {ReadOnly}Memory<T> (so that it can be stored on the heap) and then accessing its Span property once the actual bytes need to be read or written. PR dotnet/coreclr#20771 improved this by removing an argument validation branch (both for {ReadOnly}Memory<T>.Span and for {ReadOnly}Span<T>.Slice ), and while removing a branch is a small thing, in span-heavy code (such as when doing formatting and parsing), small things done over and over and over again add up. More impactful, PR dotnet/coreclr#20386 plays tricks at the runtime level to safely eliminate some of the runtime checked casting and bit masking logic that had been used to enable {ReadOnly}Memory<T> to wrap various types, like string , T[] , and MemoryManager<T> , providing a seamless veneer over all of them. The net result of these PRs is a nice speed-up when fishing a Span<T> out of a Memory<T> , which in turn improves all other operations that do so.

private ReadOnlyMemory<byte> _mem = new byte[1]; [Benchmark] public ReadOnlySpan<byte> GetSpan() => _mem.Span;

Method Toolchain Mean Error StdDev Ratio GetSpan netcoreapp2.1 3.873 ns 0.0927 ns 0.0822 ns 1.00 GetSpan netcoreapp3.0 1.843 ns 0.0401 ns 0.0375 ns 0.48

Of course, once you get a span, you want to use it, and there are a myriad of ways to use one, many of which have also been optimized further in .NET Core 3.0. For example, just as with arrays, to pass the data from a span to native code via a P/Invoke, the data needs to be pinned (unless it’s already immovable, such as if the span were created to wrap some natively allocated memory not on the GC heap or if it were created for some data on the stack). To pin a span, the easiest way is to simply rely on the C# language’s support added in C# 7.3 that supports a pattern-based way to use any type with the

fixed keyword. All a type need do is expose a GetPinnableReference method (or extension method) that returns a ref T to the data stored in that instance, and that type can be used with fixed . {ReadOnly}Span<T> does exactly this. However, even though {ReadOnly}Span<T>.GetPinnableReference generally gets inlined, a call it makes internally to Unsafe.AsRef was getting blocked from inlining; PR dotnet/coreclr#18274 fixed this, enabling the whole operation to be inlined. Further, the aforementioned code was actually tweaked in PR dotnet/coreclr#20428 to eliminate one branch on the hot path. Both of these combine to result in a measurable boost when pinning a span:

private readonly byte[] _bytes = new byte[10_000]; [Benchmark(OperationsPerInvoke = 10_000)] public unsafe int PinSpan() { Span<byte> s = _bytes; int total = 0; for (int i = 0; i < s.Length; i++) fixed (byte* p = s) // equivalent to `fixed (byte* p = &s.GetPinnableReference())` total += *p; return total; }

Method Toolchain Mean Error StdDev Ratio RatioSD PinSpan netcoreapp2.1 0.7930 ns 0.0177 ns 0.0189 ns 1.00 0.00 PinSpan netcoreapp3.0 0.6496 ns 0.0109 ns 0.0102 ns 0.82 0.03

It’s worth noting, as well, that if you’re interested in these kinds of micro-optimizations, you might also want to avoid using the default pinning at all, at least on super hot paths. The

{ReadOnly}Span<T>.GetPinnableReference method was designed to behave just like pinning of arrays and strings, where null or empty inputs result in a null pointer. This behavior requires an additional check to be performed to see whether the length of the span is zero:

// https://github.com/dotnet/coreclr/blob/52aff202cd382c233d903d432da06deffaa21868/src/System.Private.CoreLib/shared/System/Span.Fast.cs#L168-L174 [EditorBrowsable(EditorBrowsableState.Never)] public unsafe ref T GetPinnableReference() { // Ensure that the native code has just one forward branch that is predicted-not-taken. ref T ret = ref Unsafe.AsRef<T>(null); if (_length != 0) ret = ref _pointer.Value; return ref ret; }

If in your code by construction you know that the span will not be empty, you can choose to instead use

MemoryMarshal.GetReference , which performs the same operation but without the length check:

// https://github.com/dotnet/coreclr/blob/52aff202cd382c233d903d432da06deffaa21868/src/System.Private.CoreLib/shared/System/Runtime/InteropServices/MemoryMarshal.Fast.cs#L79 public static ref T GetReference<T>(Span<T> span) => ref span._pointer.Value;

Again, while a single check adds minor overhead, when executed over and over and over, that can add up:

private readonly byte[] _bytes = new byte[10_000]; [Benchmark(OperationsPerInvoke = 10_000, Baseline = true)] public unsafe int PinSpan() { Span<byte> s = _bytes; int total = 0; for (int i = 0; i < s.Length; i++) fixed (byte* p = s) // equivalent to `fixed (byte* p = &s.GetPinnableReference())` total += *p; return total; } [Benchmark(OperationsPerInvoke = 10_000)] public unsafe int PinSpanExplicit() { Span<byte> s = _bytes; int total = 0; for (int i = 0; i < s.Length; i++) fixed (byte* p = &MemoryMarshal.GetReference(s)) total += *p; return total; }

Method Mean Error StdDev Ratio RatioSD PinSpan 0.6524 ns 0.0129 ns 0.0159 ns 1.00 0.00 PinSpanExplicit 0.5200 ns 0.0111 ns 0.0140 ns 0.80 0.03

Of course, there are many other (and generally preferred) ways to operate over a span’s data than to use

fixed . For example, it’s a bit surprising that until Span<T> came along, .NET didn’t have a built-in equivalent of memcmp , but nevertheless, Span<T> ‘s SequenceEqual and SequenceCompareTo methods have become go-to methods for comparing in-memory data in .NET. In .NET Core 2.1, both SequenceEqual and SequenceCompareTo were optimized to utilize System.Numerics.Vector for vectorization, but the nature of SequenceEqual made it more amenable to best take advantage. In PR dotnet/coreclr#22127, @benaadams updated SequenceCompareTo to take advantage of the new hardware instrinsics APIs available in .NET Core 3.0 to specifically target AVX2 and SSE2, resulting in significant improvements when comparing both small and large spans. (For more information on hardware intrinsics in .NET Core 3.0, see platform-intrinsics.md and using-net-hardware-intrinsics-api-to-accelerate-machine-learning-scenarios.)

private byte[] _orig, _same, _differFirst, _differLast; [Params(16, 256)] public int Length { get; set; } [GlobalSetup] public void Setup() { _orig = Enumerable.Range(0, Length).Select(i => (byte)i).ToArray(); _same = (byte[])_orig.Clone(); _differFirst = (byte[])_orig.Clone(); _differFirst[0] = (byte)(_orig[0] + 1); _differLast = (byte[])_orig.Clone(); _differLast[_differLast.Length - 1] = (byte)(_orig[_orig.Length - 1] + 1); } [Benchmark] public int CompareSame() => _orig.AsSpan().SequenceCompareTo(_same); [Benchmark] public int CompareDifferFirst() => _orig.AsSpan().SequenceCompareTo(_differFirst); [Benchmark] public int CompareDifferLast() => _orig.AsSpan().SequenceCompareTo(_differLast);

Method Toolchain Length Mean Error StdDev Ratio CompareSame netcoreapp2.1 16 16.955 ns 0.2009 ns 0.1781 ns 1.00 CompareSame netcoreapp3.0 16 4.757 ns 0.0938 ns 0.0732 ns 0.28 CompareDifferFirst netcoreapp2.1 16 11.874 ns 0.1240 ns 0.1100 ns 1.00 CompareDifferFirst netcoreapp3.0 16 5.174 ns 0.0543 ns 0.0508 ns 0.44 CompareDifferLast netcoreapp2.1 16 16.644 ns 0.2146 ns 0.2007 ns 1.00 CompareDifferLast netcoreapp3.0 16 5.373 ns 0.0479 ns 0.0448 ns 0.32 CompareSame netcoreapp2.1 256 43.740 ns 0.8226 ns 0.7292 ns 1.00 CompareSame netcoreapp3.0 256 11.055 ns 0.1625 ns 0.1441 ns 0.25 CompareDifferFirst netcoreapp2.1 256 12.144 ns 0.0849 ns 0.0752 ns 1.00 CompareDifferFirst netcoreapp3.0 256 6.663 ns 0.1044 ns 0.0977 ns 0.55 CompareDifferLast netcoreapp2.1 256 39.697 ns 0.9291 ns 2.6054 ns 1.00 CompareDifferLast netcoreapp3.0 256 11.242 ns 0.2218 ns 0.1732 ns 0.32

As background, “vectorization” is an approach to parallelization that performs multiple operations as part of individual instructions on a single core. Some optimizing compilers can perform automatic vectorization, whereby the compiler analyzes loops to determine whether it can generate functionally equivalent code that would utilize such instructions to run faster. The .NET JIT compiler does not currently perform auto-vectorization, but it is possible to manually vectorize loops, and the options for doing so have significantly improved in .NET Core 3.0. Just as a simple example of what vectorization can look like, imagine having an array of bytes and wanting to search it for the first non-zero byte, returning the position of that byte. The simple solution is to just iterate through all of the bytes:

private byte[] _buffer = new byte[10_000].Concat(new byte[] { 42 }).ToArray(); [Benchmark(Baseline = true)] public int LoopBytes() { byte[] buffer = _buffer; for (int i = 0; i < buffer.Length; i++) { if (buffer[i] != 0) return i; } return -1; }

That of course works functionally, and for very small arrays it’s fine. But for larger arrays, we end up doing significantly more work than is actually necessary. Consider instead in a 64-bit process re-interpreting the array of bytes as an array of longs, which

Span<T> nicely supports. We then effectively compare 8 bytes at a time rather than 1 byte at a time, at the expense of added code complexity: once we find a non-zero long, we then need to look at each byte it contains to determine the position of the first non-zero one (though there are ways to improve that, too). Similarly, the array’s length may not evenly divide by 8, so we need to be able to handle the overflow.

[Benchmark] public int LoopLongs() { byte[] buffer = _buffer; int remainingStart = 0; if (IntPtr.Size == sizeof(long)) { Span<long> longBuffer = MemoryMarshal.Cast<byte, long>(buffer); remainingStart = longBuffer.Length * sizeof(long); for (int i = 0; i < longBuffer.Length; i++) { if (longBuffer[i] != 0) { remainingStart = i * sizeof(long); break; } } } for (int i = remainingStart; i < buffer.Length; i++) { if (buffer[i] != 0) return i; } return -1; }

For longer arrays, this yields really nice wins:

Method Mean Error StdDev Ratio LoopBytes 5,462.3 ns 107.093 ns 105.180 ns 1.00 LoopLongs 568.6 ns 6.895 ns 5.758 ns 0.10

I’ve glossed over some details here, but it should convey the core idea. .NET includes additional mechanisms for vectorizing as well. In particular, the aforementioned

System.Numerics.Vector type allows for a developer to write code using Vector and then have the JIT compiler translate that into the best instructions available on the current platform.

[Benchmark] public int LoopVectors() { byte[] buffer = _buffer; int remainingStart = 0; if (Vector.IsHardwareAccelerated) { while (remainingStart <= buffer.Length - Vector<byte>.Count) { var vector = new Vector<byte>(buffer, remainingStart); if (!Vector.EqualsAll(vector, default)) { break; } remainingStart += Vector<byte>.Count; } } for (int i = remainingStart; i < buffer.Length; i++) { if (buffer[i] != 0) return i; } return -1; }

Method Mean Error StdDev Ratio LoopBytes 5,462.3 ns 107.093 ns 105.180 ns 1.00 LoopLongs 568.6 ns 6.895 ns 5.758 ns 0.10 LoopVectors 306.0 ns 4.502 ns 4.211 ns 0.06

Further, .NET Core 3.0 includes new hardware intrinsics that allow a properly-motivated developer to eke out the best possible performance on supporting hardware, utilizing extensions like AVX or SSE that can compare well more than 8 bytes at a time. Many of the improvements in .NET Core 3.0 come from utilizing these techniques. Back to examples, copying spans has also improved, thanks to PRs

dotnet/coreclr#18006 from @benaadams and dotnet/coreclr#17889, in particular for relatively small spans…

private byte[] _from = new byte[] { 1, 2, 3, 4 }; private byte[] _to = new byte[4]; [Benchmark] public void CopySpan() => _from.AsSpan().CopyTo(_to);

Method Toolchain Mean Error StdDev Ratio CopySpan netcoreapp2.1 10.913 ns 0.1960 ns 0.1737 ns 1.00 CopySpan netcoreapp3.0 3.568 ns 0.0528 ns 0.0494 ns 0.33

Searching is one of the most commonly performed operations in any program, and searches with spans are generally performed with

IndexOf and its variants (e.g. IndexOfAny and Contains ) In PR dotnet/coreclr#20738, @benaadams again utilized vectorization, this time to improve the performance of IndexOfAny when operating over bytes, a particularly common case in many networking-related scenarios (e.g. parsing bytes off the wire as part of an HTTP stack). You can see the effects of this in the following microbenchmark:

private byte[] _arr = Encoding.UTF8.GetBytes("This is a test to see improvements to IndexOfAny. How'd they work?"); [Benchmark] public int IndexOf() => new Span<byte>(_arr).IndexOfAny((byte)'.', (byte)'?');

Method Toolchain Mean Error StdDev Ratio IndexOf netcoreapp2.1 12.828 ns 0.1805 ns 0.1600 ns 1.00 IndexOf netcoreapp3.0 4.504 ns 0.0968 ns 0.0858 ns 0.35

I love these kinds of improvements, because they’re low-enough in the stack that they end up having multiplicative effects across so much code. The above change only affected

byte , but subsequent PRs were submitted to cover char as well, and then PR dotnet/coreclr#20855 made a nice change that brought these same changes to other primitives of the same sizes. For example, we can recast the previous benchmark to use sbyte instead of byte, and as of that PR, a similar improvement applies:

private sbyte[] _arr = Encoding.UTF8.GetBytes("This is a test to see improvements to IndexOfAny. How'd they work?").Select(b => (sbyte)b).ToArray(); [Benchmark] public int IndexOf() => new Span<sbyte>(_arr).IndexOfAny((sbyte)'.', (sbyte)'?');

Method Toolchain Mean Error StdDev Ratio IndexOf netcoreapp2.1 24.636 ns 0.2292 ns 0.2144 ns 1.00 IndexOf netcoreapp3.0 9.795 ns 0.1419 ns 0.1258 ns 0.40

As another example, consider PR

dotnet/coreclr#20275. That change similarly utilized vectorization to improve the performance of To{Upper/Lower}{Invariant}.

private string _src = "This is a source string that needs to be capitalized."; private char[] _dst = new char[1024]; [Benchmark] public int ToUpperInvariant() => _src.AsSpan().ToUpperInvariant(_dst);

Method Toolchain Mean Error StdDev Ratio ToUpperInvariant netcoreapp2.1 64.36 ns 0.8099 ns 0.6763 ns 1.00 ToUpperInvariant netcoreapp3.0 26.48 ns 0.2411 ns 0.2137 ns 0.41

PR

dotnet/coreclr#19959 optimizes the Trim{Start/End} helpers on ReadOnlySpan<char> , another very commonly-applied method, with equally exciting results (it’s hard to see with the white space in the results, but the results in the table go in order of the arguments in the Params attribute):

[Params("", " abcdefg ", "abcdefg")] public string Data; [Benchmark] public ReadOnlySpan<char> Trim() => Data.AsSpan().Trim();

Method Toolchain Data Mean Error StdDev Ratio Trim netcoreapp2.1 12.999 ns 0.1913 ns 0.1789 ns 1.00 Trim netcoreapp3.0 3.078 ns 0.0349 ns 0.0326 ns 0.24 Trim netcoreapp2.1 abcdefg 17.618 ns 0.3534 ns 0.2951 ns 1.00 Trim netcoreapp3.0 abcdefg 7.927 ns 0.0934 ns 0.0828 ns 0.45 Trim netcoreapp2.1 abcdefg 15.522 ns 0.2200 ns 0.1951 ns 1.00 Trim netcoreapp3.0 abcdefg 5.227 ns 0.0750 ns 0.0665 ns 0.34

Sometimes optimizations are just about being smarter about code management. PR

dotnet/coreclr#17890 removed an unnecessary layer of functions that were on many globalization-related code paths, and just removing those extra unnecessary method invocations results in measurable speed-ups when working with small spans, e.g.

[Benchmark] public bool EndsWith() => "Hello world".AsSpan().EndsWith("world", StringComparison.OrdinalIgnoreCase);

Method Toolchain Mean Error StdDev Ratio EndsWith netcoreapp2.1 37.80 ns 0.3290 ns 0.2917 ns 1.00 EndsWith netcoreapp3.0 12.26 ns 0.1479 ns 0.1384 ns 0.32

Of course, one of the great things about span is that it is a reusable building-block that enables many higher-level operations. That includes operations on both arrays and strings…

Arrays and Strings

As a theme that’s emerged within .NET Core, wherever possible, new performance-focused functionality should not only be exposed for public use but also be used internally; after all, given the depth and breadth of functionality within .NET Core, if some performance-focused feature doesn’t meet the needs of .NET Core itself, there’s a reasonable chance it also won’t meet the public need. As such, internal usage of new features is a key benchmark as to whether the design is adequate, and in the process of evaluating such criteria, many additional code paths benefit, and these improvements have a multiplicative effect. This isn’t just about new APIs. Many of the language features introduced in C# 7.2, 7.3, and 8.0 are influenced by the needs of .NET Core itself and have been used to improve things that we couldn’t reasonably improve before (other than dropping down to unsafe code, which we try to avoid when possible). For example, PR dotnet/coreclr#17891 speeds up Array.Reverse by taking advantage of the C# 7.2 ref locals feature and the 7.3 ref local reassignment feature. Using the new feature allows for the code to be expressed in a way that lets the JIT generate better code for the inner loop, and in turn results in a measurable speed-up:

private int[] _arr = Enumerable.Range(0, 256).ToArray(); [Benchmark] public void Reverse() => Array.Reverse(_arr);

Method Toolchain Mean Error StdDev Ratio RatioSD Reverse netcoreapp2.1 105.06 ns 2.488 ns 7.337 ns 1.00 0.00 Reverse netcoreapp3.0 74.12 ns 1.494 ns 2.536 ns 0.66 0.02

Another example for arrays, the

Clear method improved in PR dotnet/coreclr#24302, which works around an alignment issue that results in the underlying memset used to implement the operation being up to 2x slower. The change manually clears up to a few bytes one by one, such that the pointer we then hand off to memset is properly aligned. If you got “lucky” previously and the array happened to be aligned, performance was fine, but if it wasn’t aligned, there was a non-trivial performance hit incurred. This benchmark simulates the unlucky case:

[GlobalSetup] public void Setup() { while (true) { var buffer = new byte[8192]; GCHandle handle = GCHandle.Alloc(buffer, GCHandleType.Pinned); if (((long)handle.AddrOfPinnedObject()) % 32 != 0) { _handle = handle; _buffer = buffer; return; } handle.Free(); } } [GlobalCleanup] public void Cleanup() => _handle.Free(); private GCHandle _handle; private byte[] _buffer; [Benchmark] public void Clear() => Array.Clear(_buffer, 0, _buffer.Length);

Method Toolchain Mean Error StdDev Ratio Clear netcoreapp2.1 121.59 ns 0.8349 ns 0.6519 ns 1.00 Clear netcoreapp3.0 87.91 ns 1.7768 ns 1.6620 ns 0.73

That said, many of the improvements are in fact based on new APIs. Span is a great example of this. It was introduced in .NET Core 2.1, and the initial push was to get it to be usable and expose sufficient surface area to allow it to be used meaningfully. But at the same time, we started utilizing it internally in order to both vet the design and benefit from the improvements it enables. Some of this was done in .NET Core 2.1, but the effort continues in .NET Core 3.0. Arrays and strings are both prime candidates for such optimizations. For example, many of the same vectorization optimizations applied to spans are similarly applied to arrays. PR

dotnet/coreclr#21116 from @benaadams optimized Array.{Last}IndexOf for both byte s and char s, utilizing the same internal helpers that were written to enable spans, and to similar effect:

private char[] _arr = "This is a test to see improvements to IndexOf. How'd they work?".ToCharArray(); [Benchmark] public int IndexOf() => Array.IndexOf(_arr, '.');

Method Toolchain Mean Error StdDev Ratio RatioSD IndexOf netcoreapp2.1 34.976 ns 0.6352 ns 0.5631 ns 1.00 0.00 IndexOf netcoreapp3.0 9.471 ns 0.6638 ns 1.1091 ns 0.29 0.04

And as with spans, thanks to PR

dotnet/coreclr#24293 from @dschinde, these IndexOf optimizations also now apply to other primitives of the same size.

private short[] _arr = "This is a test to see improvements to IndexOf. How'd they work?".Select(c => (short)c).ToArray(); [Benchmark] public int IndexOf() => Array.IndexOf(_arr, (short)'.');

Method Toolchain Mean Error StdDev Ratio IndexOf netcoreapp2.1 34.181 ns 0.6626 ns 0.6508 ns 1.00 IndexOf netcoreapp3.0 9.600 ns 0.1913 ns 0.1598 ns 0.28

Vectorization optimizations have been applied to strings, too. You can see the effect of PR

dotnet/coreclr#21076 from @benaadams in this microbenchmark:

[Benchmark] public int IndexOf() => "Let's see how fast we can find the period towards the end of this string. Pretty fast?".IndexOf('.', StringComparison.Ordinal);

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated IndexOf netcoreapp2.1 75.14 ns 1.5285 ns 1.6355 ns 1.00 0.0151 – – 32 B IndexOf netcoreapp3.0 11.70 ns 0.2382 ns 0.2111 ns 0.16 – – – –

Also note in the above that the .NET Core 2.1 operation allocates (due to converting the search character into a string), whereas the .NET Core 3.0 implementation does not. That’s thanks to PR

dotnet/coreclr#19788 from @benaadams. There are of course pieces of functionality that are more unique to strings (albeit also applicable to new functionality exposed on spans), such as hash code computation with various string comparison methods. For example, PR dotnet/coreclr#20309/ improved the performance of String.GetHashCode when performing OrdinalIgnoreCase operations, which along with Ordinal (the default) represent the two most common modes.

[Benchmark] public int GetHashCodeIgnoreCase() => "Some string".GetHashCode(StringComparison.OrdinalIgnoreCase);

Method Toolchain Mean Error StdDev Ratio GetHashCodeIgnoreCase netcoreapp2.1 47.70 ns 0.5751 ns 0.5380 ns 1.00 GetHashCodeIgnoreCase netcoreapp3.0 14.28 ns 0.1462 ns 0.1296 ns 0.30

OrdinalsIgnoreCase has been improved for other uses as well. For example, PR dotnet/coreclr#20734 improved String.Equals when using StringComparer.OrdinalIgnoreCase by both vectorizing (checking two chars at a time instead of one) and removing branches from an inner loop:

[Benchmark] public bool EqualsIC() => "Some string".Equals("sOME sTrinG", StringComparison.OrdinalIgnoreCase);

Method Toolchain Mean Error StdDev Ratio EqualsIC netcoreapp2.1 24.036 ns 0.3819 ns 0.3572 ns 1.00 EqualsIC netcoreapp3.0 9.165 ns 0.0589 ns 0.0551 ns 0.38

The previous cases are examples of functionality in

String ‘s implementation, but there are lots of ancillary string-related functionality that have seen improvements as well. For example, various operations on Char have been improved, such as Char.GetUnicodeCategory via PRs dotnet/coreclr#20983 and dotnet/coreclr#20864:

[Params('.', 'a', '\x05D0')] public char Char { get; set; } [Benchmark] public UnicodeCategory GetCategory() => char.GetUnicodeCategory(Char);

Method Toolchain Char Mean Error StdDev Ratio RatioSD GetCategory netcoreapp2.1 . 1.8001 ns 0.0160 ns 0.0142 ns 1.00 0.00 GetCategory netcoreapp3.0 . 0.4925 ns 0.0141 ns 0.0132 ns 0.27 0.01 GetCategory netcoreapp2.1 a 1.7925 ns 0.0144 ns 0.0127 ns 1.00 0.00 GetCategory netcoreapp3.0 a 0.4957 ns 0.0117 ns 0.0091 ns 0.28 0.01 GetCategory netcoreapp2.1 ? 3.7836 ns 0.0493 ns 0.0461 ns 1.00 0.00 GetCategory netcoreapp3.0 ? 2.7531 ns 0.0757 ns 0.0633 ns 0.73 0.02

Those PRs also highlight another case of benefiting from a language improvement. As of C# 7.3, the C# compiler is able to optimize properties of the form:

static ReadOnlySpan<byte> s_byteData => new byte[] { … /* constant bytes */ } Rather than emitting this exactly as written, which would allocate a new byte array on each call, the compiler takes advantage of the facts that a) the bytes backing the array are all constant and b) it’s being returned as a read-only span, which means the consumer is unable to mutate the data using safe code. As such, with PR dotnet/roslyn#24621, the C# compiler instead emits this by writing the bytes as a binary blob in metadata, and the property then simply creates a span that points directly to that data, making it very fast to access the data, more so even than if this property returned a static byte[].

// Run with: dotnet run -c Release -f netcoreapp2.1 --filter *Program* --runtimes netcoreapp3.0 private static byte[] ArrayProp { get; } = new byte[] { 1, 2, 3 }; [Benchmark(Baseline = true)] public ReadOnlySpan<byte> GetArrayProp() => ArrayProp; private static ReadOnlySpan<byte> SpanProp => new byte[] { 1, 2, 3 }; [Benchmark] public ReadOnlySpan<byte> GetSpanProp() => SpanProp;

Method Mean Error StdDev Median Ratio GetArrayProp 1.3362 ns 0.0498 ns 0.0416 ns 1.3366 ns 1.000 GetSpanProp 0.0125 ns 0.0132 ns 0.0110 ns 0.0080 ns 0.009

Another string-related area that’s gotten some attention is

StringBuilder (not necessarily improvements to StringBuilder itself, although it has received some of those, for example a new overload in PR dotnet/coreclr#20773 from @Wraith2 that helps avoid accidentally boxing and creating a string from a ReadOnlyMemory<char> appended to the builder). Rather, in many situations StringBuilder s have been used for convenience but added cost, and with just a little work (and in some cases the new String.Create method introduced in .NET Core 2.1), we can eliminate that overhead, in both CPU usage and allocation. Here a few examples… * PR dotnet/corefx#33598 removed a StringBuilder used in marshaling from Dns.GetHostEntry :

[Benchmark] public IPHostEntry GetHostEntry() => Dns.GetHostEntry("34.206.253.53");

Method Toolchain Mean Error StdDev Median Ratio RatioSD Gen 0 Gen 1 Gen 2 Allocated GetHostEntry netcoreapp2.1 532.7 us 16.59 us 46.79 us 526.8 us 1.00 0.00 1.9531 – – 4888 B GetHostEntry netcoreapp3.0 527.7 us 12.85 us 37.06 us 542.8 us 1.00 0.11 – – – 616 B

PR dotnet/coreclr#21122 removed a StringBuilder used in Hebrew number formatting:

private static CultureInfo CreateCulture() { var c = new CultureInfo("he-IL"); c.DateTimeFormat.Calendar = new HebrewCalendar(); return c; } private CultureInfo _hebrewIsrael = CreateCulture(); [Benchmark] public string FormatHebrew() => new DateTime(2018, 11, 20).ToString(_hebrewIsrael);

Method Toolchain Mean Error StdDev Ratio RatioSD Gen 0 Gen 1 Gen 2 Allocated FormatHebrew netcoreapp2.1 626.0 ns 7.917 ns 7.405 ns 1.00 0.00 0.2890 – – 608 B FormatHebrew netcoreapp3.0 570.6 ns 10.504 ns 9.825 ns 0.91 0.02 0.1554 – – 328 B

PR dotnet/corefx#33592 removed a StringBuilder used in PhysicalAddress formatting:

private readonly PhysicalAddress _short = new PhysicalAddress(new byte[1] { 42 }); private readonly PhysicalAddress _long = new PhysicalAddress(Enumerable.Range(0, 256).Select(i => (byte)i).ToArray()); [Benchmark] public void PAShort() => _short.ToString(); [Benchmark] public void PALong() => _long.ToString();

Method Toolchain Mean Error StdDev Ratio RatioSD Gen 0 Gen 1 Gen 2 Allocated PAShort netcoreapp2.1 33.68 ns 1.0378 ns 2.9271 ns 1.00 0.00 0.0648 – – 136 B PAShort netcoreapp3.0 17.12 ns 0.4240 ns 0.7313 ns 0.55 0.04 0.0153 – – 32 B PALong netcoreapp2.1 2,761.80 ns 50.1515 ns 46.9117 ns 1.00 0.00 1.1940 – – 2512 B PALong netcoreapp3.0 787.78 ns 27.4673 ns 80.1234 ns 0.31 0.01 0.5007 – – 1048 B

PR dotnet/corefx#29605 removed StringBuilder s from various properties of X509Certificate :

private X509Certificate2 _cert = GetCert(); private static X509Certificate2 GetCert() { using (var client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)) { client.Connect("microsoft.com", 443); using (var ssl = new SslStream(new NetworkStream(client))) { ssl.AuthenticateAsClient("microsoft.com", null, SslProtocols.None, false); return new X509Certificate2(ssl.RemoteCertificate); } } } [Benchmark] public string CertProp() => _cert.Thumbprint;

Method Toolchain Mean Error StdDev Median Ratio RatioSD Gen 0 Gen 1 Gen 2 Allocated CertProp netcoreapp2.1 209.30 ns 4.464 ns 10.435 ns 204.35 ns 1.00 0.00 0.1256 – – 264 B CertProp netcoreapp3.0 95.82 ns 1.822 ns 1.704 ns 96.43 ns 0.45 0.02 0.0497 – – 104 B

and so on. These PRs demonstrate that good gains can be had simply by making small tweaks that make existing code paths cheaper, and that expands well beyond

StringBuilder . There are lots of places within .NET Core, for example, where String.Substring is used, and many of those cases can be replaced with use of AsSpan and Slice , for example as was done in PR dotnet/corefx#29402 by @juliushardt, or PRs dotnet/coreclr#17916 and dotnet/corefx#29539, or as was done in PRs dotnet/corefx#29227 and dotnet/corefx#29721 to remove string allocations from FileSystemWatcher, delaying the creation of such strings until only when it was known they were absolutely necessary.

[Benchmark] public void HtmlDecode() => WebUtility.HtmlDecode("水水水水水水水");

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated HtmlDecode netcoreapp2.1 638.2 ns 8.474 ns 7.077 ns 1.00 0.1516 – – 320 B HtmlDecode netcoreapp3.0 153.7 ns 2.776 ns 2.461 ns 0.24 0.0191 – – 40 B

Another example of using new APIs to improve existing functionality is with

String.Concat . .NET Core 3.0 has several new String.Concat overloads, ones that accept ReadOnlySpan<char> instead of string . These make it easy to avoid allocations/copies of substrings in cases where concatenating pieces of other strings: instead of using String.Concat with String.Substring , it’s used instead with String.AsSpan(...) or Slice . In fact, the PRs dotnet/coreclr#21766 and dotnet/corefx#34451 that implemented, exposed, and added tests for these new overloads also added tens of call sites to the new overloads across .NET Core. Here’s an example of the impact one of those has, improving the performance of accessing Uri.DnsSafeHost :

[Benchmark] public string DnsSafeHost() => new Uri("http://[fe80::3]%1").DnsSafeHost;

Method Toolchain Mean Error StdDev Ratio RatioSD Gen 0 Gen 1 Gen 2 Allocated DnsSafeHost netcoreapp2.1 733.7 ns 14.448 ns 17.20 ns 1.00 0.00 0.2012 – – 424 B DnsSafeHost netcoreapp3.0 450.1 ns 9.013 ns 18.41 ns 0.63 0.02 0.1059 – – 224 B

Another example, using

Path.ChangeExtension to change from one non-null extension to another:

[Benchmark] public string ChangeExtension() => Path.ChangeExtension("filename.txt", ".dat");

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated ChangeExtension netcoreapp2.1 30.57 ns 0.7124 ns 0.6664 ns 1.00 0.0495 – – 104 B ChangeExtension netcoreapp3.0 24.54 ns 0.3398 ns 0.2838 ns 0.80 0.0229 – – 48 B

Finally, a very closely related area is that of encoding. A bunch of improvements were made in .NET Core 3.0 around

Encoding , both in general and for specific encodings, such as PR dotnet/coreclr#18263 that allowed an existing corner-case optimization to be applied for Encoding.Unicode.GetString in many more cases, or dotnet/coreclr#18487 that removed a bunch of unnecessary virtual indirections from various encoding implementations, or PR dotnet/coreclr#20768 that improved the performance of Encoding.Preamble by taking advantage of the same metadata-blob span support discussed earlier, or PRs dotnet/coreclr#21948 and dotnet/coreclr#23098 that overhauled and streamlined the implementions of UTF8Encoding and AsciiEncoding .

private byte[] _data = Encoding.ASCII.GetBytes("This is a test of ASCII encoding. It's faster now."); [Benchmark] public string ASCII() => Encoding.ASCII.GetString(_data);

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated ASCII netcoreapp2.1 66.92 ns 0.8942 ns 0.8364 ns 1.00 0.0609 – – 128 B ASCII netcoreapp3.0 28.04 ns 0.6325 ns 0.9467 ns 0.42 0.0612 – – 128 B

These examples all served to highlight improvements made in and around strings. That’s all well and good, but where the improvements related to strings really start to shine is when looking at improvements around formatting and parsing.

Parsing/Formatting

Parsing and formatting are the lifeblood of any modern web app or service: take data off the wire, parse it, manipulate it, format it back out. As such, in .NET Core 2.1 along with bringing up Span<T> , we invested in the formatting and parsing of primitives, from Int32 to DateTime . Many of those changes can be read about in my previous blog posts, but one of the key factors in enabling those performance improvements was in moving a lot of native code to managed. That may be counter-intuitive, in that it’s “common knowledge” that C code is faster than C# code. However, in addition to the gap between them narrowing, having (mostly) safe C# code has made the code base easier to experiment in, so whereas we may have been skittish about tweaking the native implementations, the community-at-large has dived head first into optimizing these implementations wherever possible. That effort continues in full force in .NET Core 3.0, with some very nice rewards reaped. Let’s start with core integer primitives. PR dotnet/coreclr#18897 added a variety of special paths for the parsing of Integer -style signed values (e.g. Int32 and Int64 ), PR dotnet/coreclr#18930 added similar support for unsigned (e.g. UInt32 and UInt64 ), and PR dotnet/coreclr#18952 did a similar pass for hex. On top of those, PR dotnet/coreclr#21365 layered in additional optimizations, for example utilizing those changes for primitives like byte , skipping unnecessary layers of functions, streamlining some calls to improve inlining, and further reducing branching. The net impact here are some significant improvements to the performance of parsing integer primitive types in this release.

[Benchmark] public int ParseInt32Dec() => int.Parse("12345678"); [Benchmark] public int ParseInt32Hex() => int.Parse("BC614E", NumberStyles.HexNumber);

Method Toolchain Mean Error StdDev Ratio ParseInt32Dec netcoreapp2.1 77.30 ns 0.8710 ns 0.8147 ns 1.00 ParseInt32Dec netcoreapp3.0 16.08 ns 0.2168 ns 0.2028 ns 0.21 ParseInt32Hex netcoreapp2.1 69.01 ns 1.0024 ns 0.9377 ns 1.00 ParseInt32Hex netcoreapp3.0 17.39 ns 0.1123 ns 0.0995 ns 0.25

Formatting of such types was also improved, even though it had already been improved significantly between .NET Core 2.0 and .NET Core 2.1. PR

dotnet/coreclr#19551 tweaked the structure of the code to avoid needing to access the current culture number formatting data if it wouldn’t be needed (e.g. when formatting a value as hex, there’s no customization based on current culture), and PR dotnet/coreclr#18935 improved decimal formatting performance, in large part by optimizing how data is passed around (or not passed at all).

[Benchmark] public string DecimalToString() => 12345.6789m.ToString();

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated DecimalToString netcoreapp2.1 88.79 ns 1.4034 ns 1.3127 ns 1.00 0.0228 – – 48 B DecimalToString netcoreapp3.0 76.62 ns 0.5957 ns 0.5572 ns 0.86 0.0228 – – 48 B

In fact,

System.Decimal itself has been overhauled in .NET Core 3.0, as of PR dotnet/coreclr#18948 now with an entirely managed implementation, and with additional performance work in PRs like dotnet/coreclr#20305.

private decimal _a = 67891.2345m; private decimal _b = 12345.6789m; [Benchmark] public decimal Add() => _a + _b; [Benchmark] public decimal Subtract() => _a - _b; [Benchmark] public decimal Multiply() => _a * _b; [Benchmark] public decimal Divide() => _a / _b; [Benchmark] public decimal Mod() => _a % _b; [Benchmark] public decimal Floor() => decimal.Floor(_a); [Benchmark] public decimal Round() => decimal.Round(_a);

Method Toolchain Mean Error StdDev Median Ratio RatioSD Add netcoreapp2.1 12.021 ns 0.6813 ns 2.0088 ns 11.507 ns 1.00 0.00 Add netcoreapp3.0 8.300 ns 0.0553 ns 0.0518 ns 8.312 ns 0.87 0.04 Subtract netcoreapp2.1 13.026 ns 0.2599 ns 0.2431 ns 13.046 ns 1.00 0.00 Subtract netcoreapp3.0 8.613 ns 0.2024 ns 0.2770 ns 8.488 ns 0.66 0.03 Multiply netcoreapp2.1 19.215 ns 0.2813 ns 0.2631 ns 19.229 ns 1.00 0.00 Multiply netcoreapp3.0 7.182 ns 0.1795 ns 0.2457 ns 7.131 ns 0.38 0.01 Divide netcoreapp2.1 196.827 ns 4.3572 ns 4.6621 ns 194.721 ns 1.00 0.00 Divide netcoreapp3.0 75.456 ns 1.5301 ns 1.7007 ns 75.089 ns 0.38 0.01 Mod netcoreapp2.1 464.968 ns 7.0295 ns 6.5754 ns 466.825 ns 1.00 0.00 Mod netcoreapp3.0 13.756 ns 0.2476 ns 0.2316 ns 13.729 ns 0.03 0.00 Floor netcoreapp2.1 33.593 ns 0.8348 ns 2.2710 ns 32.734 ns 1.00 0.00 Floor netcoreapp3.0 12.109 ns 0.1325 ns 0.1239 ns 12.085 ns 0.33 0.02 Round netcoreapp2.1 32.181 ns 0.5660 ns 0.5294 ns 32.018 ns 1.00 0.00 Round netcoreapp3.0 12.798 ns 0.1572 ns 0.1394 ns 12.808 ns 0.40 0.01

Back to formatting and parsing, there are even some new formatting special-cases that might look silly at first, but that represent optimizations targeting real-world cases. In some sizeable web applications, we found that a large number of strings on the managed heap were simple integral values like “0” and “1”. And since the fastest code is code you don’t need to execute at all, why bother allocating and formatting these small numbers over and over when we can instead just cache and reuse the results (effectively our own string interning pool)? That’s what PR

dotnet/coreclr#18383 does, creating a small, specialized cache of the strings for “0” through “9”, and any time we now find ourselves formatting a single-digit integer primitive, we instead just grab the relevant string from this cache.

private int _digit = 4; [Benchmark] public string SingleDigitToString() => _digit.ToString();

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated SingleDigitToString netcoreapp2.1 17.72 ns 0.3273 ns 0.3061 ns 1.00 0.0152 – – 32 B SingleDigitToString netcoreapp3.0 11.57 ns 0.1750 ns 0.1551 ns 0.65 – – – –

Enums have also seen sizable parsing and formatting improvements in .NET Core 3.0. PR

dotnet/coreclr#21214 improved the handling of Enum.Parse and Enum.TryParse , for both the generic and non-generic variants. PR dotnet/coreclr#21254 improved the performance of ToString when dealing with [Flags] enums, and PR dotnet/coreclr#21284 further improved other ToString cases. The net effect of these changes is a sizeable improvement in Enum -related performance:

[Benchmark] public DayOfWeek EnumParse() => Enum.Parse<DayOfWeek>("Thursday"); [Benchmark] public string EnumToString() => NumberStyles.Integer.ToString();

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated EnumParse netcoreapp2.1 154.42 ns 1.6917 ns 1.5824 ns 1.00 0.0114 – – 24 B EnumParse netcoreapp3.0 62.92 ns 1.2239 ns 1.1448 ns 0.41 – – – – EnumToString netcoreapp2.1 85.81 ns 1.6458 ns 1.3743 ns 1.00 0.0305 – – 64 B EnumToString netcoreapp3.0 27.89 ns 0.6076 ns 0.7901 ns 0.32 0.0114 0.0001 – 24 B

In .NET Core 2.1,

DateTime.TryFormat and ToString were optimized for the commonly-used “o” and “r” formats; in .NET Core 3.0, the parsing equivalents get a similar treatment. PR dotnet/coreclr#18800 significantly improves the performance of parsing DateTime{Offset} s formatted with the Roundtrip “o” format, and PR dotnet/coreclr#18771 does the same for the RFC1123 “r” format. For any serialization formats heavy in DateTime s, these improvements can make a substantial impact:

private string _r = DateTime.Now.ToString("r"); private string _o = DateTime.Now.ToString("o"); [Benchmark] public DateTime ParseR() => DateTime.ParseExact(_r, "r", null); [Benchmark] public DateTime ParseO() => DateTime.ParseExact(_o, "o", null);

Method Toolchain Mean Error StdDev Median Ratio Gen 0 Gen 1 Gen 2 Allocated ParseR netcoreapp2.1 2,254.6 ns 44.340 ns 45.534 ns 2,263.2 ns 1.00 0.0420 – – 96 B ParseR netcoreapp3.0 113.7 ns 3.440 ns 9.926 ns 112.6 ns 0.06 – – – – ParseO netcoreapp2.1 1,337.1 ns 26.542 ns 68.987 ns 1,363.8 ns 1.00 0.0744 – – 160 B ParseO netcoreapp3.0 354.9 ns 4.801 ns 3.748 ns 354.9 ns 0.30 – – – –

Tying back to the

StringBuilder discussion from earlier, default DateTime formatting was also improved by PR dotnet/coreclr#22111, tweaking how DateTime internally interacts with a StringBuilder that’s used to build up the resulting state.

private DateTime _now = DateTime.Now; [Benchmark] public string DateTimeToString() => _now.ToString();

Method Toolchain Mean Error StdDev Ratio RatioSD Gen 0 Gen 1 Gen 2 Allocated DateTimeToString netcoreapp2.1 337.8 ns 6.560 ns 5.815 ns 1.00 0.00 0.0834 – – 176 B DateTimeToString netcoreapp3.0 269.4 ns 5.274 ns 5.416 ns 0.80 0.02 0.0300 – – 64 B

TimeSpan formatting was also significantly improved, via PR dotnet/coreclr#18990:

private TimeSpan _ts = new TimeSpan(3, 10, 2, 34, 567); [Benchmark] public string TimeSpanToString() => _ts.ToString();

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated TimeSpanToString netcoreapp2.1 151.11 ns 2.0037 ns 1.874 ns 1.00 0.0303 – – 64 B TimeSpanToString netcoreapp3.0 34.73 ns 0.7680 ns 1.304 ns 0.23 0.0305 – – 64 B

Guid parsing also got in the perf-optimization game, with PR dotnet/coreclr#20183 improved parsing performance of Guid , primarily by avoiding overhead in helper routines, as well as by avoiding some searches used to determine which parsing routines to employ.

private string _guid = Guid.NewGuid().ToString("D"); [Benchmark] public Guid ParseGuid() => Guid.ParseExact(_guid, "D");

Method Toolchain Mean Error StdDev Median Ratio ParseGuid netcoreapp2.1 287.5 ns 11.606 ns 28.688 ns 277.2 ns 1.00 ParseGuid netcoreapp3.0 111.7 ns 2.199 ns 2.057 ns 112.4 ns 0.33

Related, PR

dotnet/coreclr#21336 again takes advantage of vectorization to improve Guid ‘s construction and formatting to and from byte arrays and spans:

private Guid _guid = Guid.NewGuid(); private byte[] _buffer = new byte[16]; [Benchmark] public void GuidToFromBytes() { _guid.TryWriteBytes(_buffer); _guid = new Guid(_buffer); }

Method Toolchain Mean Error StdDev Ratio GuidToFromBytes netcoreapp2.1 16.623 ns 0.2917 ns 0.2586 ns 1.00 GuidToFromBytes netcoreapp3.0 5.701 ns 0.1047 ns 0.0980 ns 0.34

Regular Expressions

Often related to parsing is the area of regular expressions. A bit of work was done on System.Text.RegularExpressions in .NET Core 3.0. PR dotnet/corefx#30474 replaced some usage of an internal StringBuilder cache with a ref struct -based builder that takes advantage of stack-allocated space and pooled buffers. And PR dotnet/corefx#30632 continued the effort by taking further advantage of spans. But the biggest improvement came in PR dotnet/corefx#32899 from @Alois-xx, which tweaks the code generated for a RegexOptions.Compiled Regex to avoid gratuitous thread-local accesses to look up the current culture. This is particularly impactful when also using RegexOptions.IgnoreCase . To see the impact, I found a complicated Regex that used both Compiled and IgnoreCase , and put it into a benchmark:

// Pattern and options copied from https://github.com/microsoft/referencesource/blob/aaca53b025f41ab638466b1efe569df314f689ea/System.ComponentModel.DataAnnotations/DataAnnotations/EmailAddressAttribute.cs#L54-L55 private Regex _regex = new Regex( @"^((([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+(\.([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+)*)|((\x22)((((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(([\x01-\x08\x0b\x0c\x0e-\x1f\x7f]|\x21|[\x23-\x5b]|[\x5d-\x7e]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(\\([\x01-\x09\x0b\x0c\x0d-\x7f]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]))))*(((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(\x22)))@((([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.)+(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.?$", RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.ExplicitCapture); [Benchmark] public bool RegexCompiled() => _regex.IsMatch("someAddress@someCompany.com");

Method Toolchain Mean Error StdDev Ratio RatioSD RegexCompiled netcoreapp2.1 1.946 us 0.0406 us 0.0883 us 1.00 0.00 RegexCompiled netcoreapp3.0 1.209 us 0.0432 us 0.1254 us 0.64 0.08

Threading

Threading is one of those things that’s ever-present and yet most apps and libraries don’t need to explicitly interact with most of the time. That makes it an area ripe for runtime performance improvements to drive down overhead as much as possible, so that user code just gets faster. Previous releases of .NET Core saw a lot of investment in this area, and .NET Core 3.0 continues the trend. This is another area where new APIs have been exposed and then also used in .NET Core itself for further gain. For example, historically the only work item types that could be queued to the ThreadPool were ones implemented in the runtime, namely those created by ThreadPool.QueueUserWorkItem and friends, by Task , by Timer , and other such core types. But in .NET Core 3.0, the ThreadPool has an UnsafeQueueUserWorkItem overload that accepts the newly public IThreadPoolWorkItem interface. This interface is very simple, with a single method that just Execute s work, and that means that any object that implements this interface can be queued directly to the thread pool. This is advanced; most code is just fine using the existing work item types. But this additional option affords a lot of flexibility, in particular in being able to implement the interface on a reusable object that can be queued over and over again to the pool. This is now used in a bunch of additional places in .NET Core 3.0. One such place is in System.Threading.Channels . The Channels library introduced in .NET Core 2.1 already had a fairly low allocation profile, but there were still times it would allocate. For example, one of the options when creating a channel is whether continuations created by the library should run synchronously or asynchronously as part of a task completing (e.g. when a TryWrite call on a channel wakes up a corresponding ReadAsync , whether the continuation from that ReadAsync invoked synchronously or queued by the TryWrite call). The default is that continuations are never invoked synchronously, but that also then requires allocating an object as part of queueing the continuation to the thread pool. With PR dotnet/corefx#33080, the reusable IValueTaskSource implementation that already backs the ValueTask s returned from ReadAsync calls also implements IThreadPoolWorkItem and can thus itself be queued, avoiding that allocation. This can have a measurable impact on throughput.

// Run with: dotnet run -c Release -f netcoreapp2.1 --filter *Program* private sealed class Config : ManualConfig // also add [Config(typeof(Config))] to the Program class { public Config() { Add(Job.MediumRun.With(CsProjCoreToolchain.NetCoreApp21).WithNuGet("System.Threading.Channels", "4.5.0").WithId("4.5.0")); Add(Job.MediumRun.With(CsProjCoreToolchain.NetCoreApp30).WithNuGet("System.Threading.Channels", "4.6.0-preview5.19224.8").WithId("4.6.0-preview5.19224.8")); } } private Channel<int> _channel1 = Channel.CreateUnbounded<int>(); private Channel<int> _channel2 = Channel.CreateUnbounded<int>(); [GlobalSetup] public void Setup() { Task.Run(async () => { var reader = _channel1.Reader; var writer = _channel2.Writer; while (true) { writer.TryWrite(await reader.ReadAsync()); } }); } [Benchmark] public async Task PingPong() { var writer = _channel1.Writer; var reader = _channel2.Reader; for (int i = 0; i < 10_000; i++) { writer.TryWrite(i); await reader.ReadAsync(); } }

Method Job NuGetReferences Toolchain Mean Error StdDev Gen 0 Gen 1 Gen 2 PingPong 4.5.0 System.Threading.Channels 4.5.0 .NET Core 2.1 22.44 ms 0.3246 ms 0.4757 ms 593.7500 – – PingPong 4.6.0-preview5.19224.8 System.Threading.Channels 4.6.0-preview5.19224.8 .NET Core 3.0 16.81 ms 0.4246 ms 0.6356 ms 31.2500 – –

IThreadPoolWorkItem is now also utilized in other places, like in ConcurrentExclusiveSchedulerPair (a little known but useful type that provides an exclusive scheduler that limits execution to only one task at a time, a concurrent scheduler that limits a user-defined number of tasks to run at a time, and that coordinate with each other so that no concurrent tasks may run while an exclusive task is running, ala a reader-writer lock), which now implements IThreadPoolWorkItem on an internally reusable work item object such that it also can avoid allocations when queueing its own processors. It’s also used in ASP.NET Core, and is one of the reasons key ASP.NET benchmarks are ammortized to 0 allocations per request. But by far the most impactful new implementer is in the async/await infrastructure. In .NET Core 2.1, the runtime’s support for async/await was overhauled, drastically reducing the overheads involved in async methods. Previously when an async method awaited for the first time an awaitable that wasn’t yet complete, the struct-based state machine for the async method would be boxed (literally a runtime box) to the heap. With .NET Core 2.1, we changed that to instead use a generic object that stores the struct as a field on it. This has a myriad of benefits, but one of these benefits is that it now enables us to implement additional interfaces on that object, such as implementing IThreadPoolWorkItem . PR dotnet/coreclr#20159 does exactly that, and it enables another large swath of scenarios to have further reduced allocations, in particular situations where TaskCreationOptions.RunContinuationsAsynchronously was used with a TaskCompletionSource<T> . This can be seen in a benchmark like the following.

// Run with: dotnet run -c Release -f netcoreapp2.1 --filter *Program* private sealed class Config : ManualConfig // also add [Config(typeof(Config))] to the Program class { public Config() { Add(Job.MediumRun.With(CsProjCoreToolchain.NetCoreApp21).WithNuGet("System.Threading.Channels", "4.5.0").WithId("4.5.0")); Add(Job.MediumRun.With(CsProjCoreToolchain.NetCoreApp30).WithNuGet("System.Threading.Channels", "4.6.0-preview5.19224.8").WithId("4.6.0-preview5.19224.8")); } } private Channel<TaskCompletionSource<bool>> _channel = Channel.CreateUnbounded<TaskCompletionSource<bool>>(); [GlobalSetup] public void Setup() { Task.Run(async () => { var reader = _channel.Reader; while (true) (await reader.ReadAsync()).TrySetResult(true); }); } [Benchmark] public async Task AsyncAllocs() { var writer = _channel.Writer; for (int i = 0; i < 1_000_000; i++) { var tcs = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously); writer.TryWrite(tcs); await tcs.Task; } }

Method Job NuGetReferences Toolchain Mean Error StdDev Gen 0 Gen 1 Gen 2 AsyncAllocs 4.5.0 System.Threading.Channels 4.5.0 .NET Core 2.1 2.396 s 0.0486 s 0.0728 s 96000.0000 – – AsyncAllocs 4.6.0-preview5.19224.8 System.Threading.Channels 4.6.0-preview5.19224.8 .NET Core 3.0 1.512 s 0.0256 s 0.0359 s 49000.0000 – –

That change allowed subsequent optimizations, such as PR

dotnet/coreclr#20186 using it to make await Task.Yield(); allocation-free:

[Benchmark] public async Task Yield() { for (int i = 0; i < 1_000_000; i++) { await Task.Yield(); } }

Method Toolchain Mean Error StdDev Ratio RatioSD Gen 0 Yield netcoreapp2.1 581.3 ms 11.615 ms 30.39 ms 1.00 0.00 19000.0000 Yield netcoreapp3.0 464.4 ms 9.087 ms 10.46 ms 0.81 0.06 –

It’s even utilized further in

Task itself. There’s an interesting race condition that has to be handled in awaitables: what happens if the awaited operation completes after the call to IsCompleted but before the call to OnCompleted ? As a reminder, the code:

await something;

compiles down to code along the lines of:

var $awaiter = something.GetAwaiter(); if (!$awaiter.IsCompleted) { _state = 42; AwaitOnCompleted(ref $awaiter); return; } Label42: $awaiter.GetResult();

Once we go down the path of

IsCompleted having returned false , we’re going to call AwaitOnCompleted and return. If the operation has completed by the time we call AwaitOnCompleted , we don’t want to synchronously invoke the continuation that re-enters this state machine, as we’ll be doing so further down the stack, and if that happened repeatedly, we’d “stack dive” and could end up overflowing the stack. Instead, we’re forced to queue the continuation. This case isn’t the common case, but it happens more often than you might expect, as it simply requires an operation that completes asynchronously very quickly (various networking operations often fall into this category). As of PR dotnet/coreclr#22373, the runtime now takes advantage of the async state machine box object implementing IThreadPoolWorkItem to avoid the allocations in this case as well! In addition to IThreadPoolWorkItem being used with async/await to allow the async implementation to queue work items to the thread pool in a more allocation-friendly manner just as any other code can, changes were also made that give the ThreadPool 1st-hand knowledge of the state machine box in order to help it optimize additional cases. PR dotnet/coreclr#21159 from @benaadams teaches the ThreadPool to re-route some UnsafeQueueUserWorkItem(Action<object>, object, bool) calls to instead use UnsafeQueueUserWorkItem(IAsyncStateMachineBox, bool) under the covers, so that higher-level libraries can get these allocation benefits without having to be aware of the box machinery. Another async-related area that’s seen measurable improvements are Timer s. In .NET Core 2.1, some important improvements were made to System.Threading.Timers to help improve throughput and minimize contention for a common case where timers aren’t firing, but instead are quickly created and destroyed. And while those changes help a bit with the case when timers do actually fire, they didn’t help with the majority costs and sources of contention in that case, which is that potentially a lot of work (proportional to the number of timers registered) was done while holding locks. .NET Core 3.0 makes some big improvements here. PR dotnet/coreclr#20302 partitions the internal list of registered timers into two lists: one with timers that will soon fire and one with timers that won’t fire for a while. In most workloads that have a lot of registered timers, the majority of timers fall into the latter bucket at any given point in time, and this partitioning scheme enables the runtime to only consider the small bucket when firing timers most of the time. In doing so, it can significantly reduce the costs involved in firing timers, and as a result, also significantly reduce contention on the lock held while manipulating those lists. One customer who tried out these changes after having experienced issues due to tons of active timers had this to say about the impact:

> “We got the change in production yesterday and the results are amazing, with 99% reduction in lock contention. We have also measured 4-5% CPU gains, and more importantly 0.15% improvement in reliability for our service (which is huge!).” >

The nature of the scenario makes it a little difficult to see the impact in a Benchmark.NET benchmark, so we’ll do something a little different. Rather than measuring the thing that was actually changed, we’ll measure something else that’s indirectly impacted. In particular, these changes didn’t directly impact the performance of creating and destroying timers; in fact, one of the goals was to avoid doing so (in particular to avoid harming that important path). But by reducing the costs of firing timers, we reduce how long locks are held, which then also reduces the contention that the creating/destroying of timers faces. So, our benchmark creates a bunch of timers, ranging in when and how often they fire, and then we time how long it takes to create and destroy a bunch of additional timers.

private Timer[] _timers; [GlobalSetup] public void Setup() { _timers = new Timer[1_000_000]; for (int i = 0; i < _timers.Length; i++) { _timers[i] = new Timer(_ => { }, null, i, i); } Thread.Sleep(1000); } [Benchmark] public void CreateDestroy() { for (int i = 0; i < 1_000; i++) { new Timer(_ => { }, 0, 100, 100).Dispose(); } }

Method Toolchain Mean Error StdDev Median Ratio RatioSD Gen 0 CreateDestroy netcoreapp2.1 289.1 us 7.131 us 20.687 us 282.8 us 1.00 0.00 80.0781 CreateDestroy netcoreapp3.0 199.5 us 3.983 us 5.584 us 199.2 us 0.71 0.04 80.3223

Timer improvements have also taken other forms. For example, PR dotnet/coreclr#22233 from @benaadams shrinks the allocation involved in Task.Delay when used without a CancellationToken by 24 bytes, and PR dotnet/coreclr#20509 reduces the timer-related allocations involved in creating timed CancellationTokenSource s, which also has a nice effect on throughput:

[Benchmark] public void CTSTimer() { using (var cts = new CancellationTokenSource()) cts.CancelAfter(1_000_000); }

Method Toolchain Mean Error StdDev Median Ratio RatioSD Gen 0 Gen 1 Gen 2 Allocated CTSTimer netcoreapp2.1 231.3 ns 6.293 ns 16.018 ns 224.8 ns 1.00 0.00 0.0987 – – 208 B CTSTimer netcoreapp3.0 115.3 ns 1.769 ns 1.655 ns 115.0 ns 0.46 0.04 0.0764 – – 160 B

There are other even lower-level improvements that have gone into the release. For example, PR

dotnet/coreclr#21328 from @benaadams improved Thread.CurrentThread by changing the implementation to store the relevant Thread in a [ThreadStatic] field rather than forcing CurrentThread to make an InternalCall into the native portions of the runtime.

[Benchmark] public Thread CurrentThread() => Thread.CurrentThread;

Method Toolchain Mean Error StdDev Ratio RatioSD CurrentThread netcoreapp2.1 6.101 ns 0.2587 ns 0.7547 ns 1.00 0.00 CurrentThread netcoreapp3.0 2.822 ns 0.0439 ns 0.0389 ns 0.45 0.04

As other examples, PR

dotnet/coreclr#23747 taught the runtime to better respect Docker –cpu limits, PRs dotnet/coreclr#21722 and dotnet/coreclr#21586 improved spinning behavior when contention was encountered across a variety of synchronization sites, PR dotnet/coreclr#22686 improved performance of SemaphoreSlim when consumers of an instance were mixing both synchronous Wait s and asynchronous WaitAsync s, and PR dotnet/coreclr#18098 from @Quogu special-cased CancellationTokenSource created with a timeout of 0 to avoid Timer -related costs.

Collections

Moving on from threading, let’s explore some of the performance improvements that have gone into collections. Collections are so commonly used in pretty much every program that they’ve received a lot of performance-focused attention in previous .NET Core releases. Even so, there continues to be areas for improvement. Here are some example such improvements in .NET Core 3.0.

ConcurrentDictionary<TKey, TValue> has an IsEmpty property that states whether the dictionary is empty at that moment-in-time. In previous releases, it took all of the dictionary’s locks in order to get a proper moment-in-time answer. But as it turns out, those locks only need to be held if we think the collection might be empty: if we see anything in any of the dictionary’s internals buckets, the locks aren’t needed, as we’d stop looking at additional buckets anyway the moment we found one bucket to contain anything. Thus, PR dotnet/corefx#30098 from @drewnoakes added a fast path that first checks each bucket without the locks, in order to optimize for the common case where the dictionary isn’t empty (the impact on the case where the dictionary is empty is minimal).

private ConcurrentDictionary<int, int> _cd; [GlobalSetup] public void Setup() { _cd = new ConcurrentDictionary<int, int>(); _cd.TryAdd(1, 1); } [Benchmark] public bool IsEmpty() => _cd.IsEmpty;

Method Toolchain Mean Error StdDev Ratio IsEmpty netcoreapp2.1 73.675 ns 0.3934 ns 0.3285 ns 1.00 IsEmpty netcoreapp3.0 3.160 ns 0.0402 ns 0.0356 ns 0.04

ConcurrentDictionary wasn’t the only concurrent collection to get some attention. An improvement came to ConcurrentQueue<T> in dotnet/coreclr#18035, and it’s an interesting example in how performance optimization often is a trade-off between scenarios. In .NET Core 2.0, we overhauled the ConcurrentQueue implementation in a way that significantly improved throughput while also significantly reducing memory allocations, turning the ConcurrentQueue into a linked list of circular arrays. However, the change involved a concession: because of the producer/consumer nature of the arrays, if any operation needed to observe data in-place in a segment (rather than dequeueing it), the segment that was observed would be “frozen” for any further enqueues… this was to avoid problems where, for example, one thread was enumerating the contents of the segment while another thread was enqueueing and dequeueing. When there were multiple segments in the queue, accessing Count ended up being treated as an observation, but that meant that simply accessing the ConcurrentQueue ‘s Count would render all of the multiple segments in the queue dead for further enqueues. The theory at the time was that such a trade-off was fine, because no one should be accessing the Count of the queue frequently enough for this to matter. That theory was wrong, and several customers reported significant slowdowns in their workloads because they were accessing the Count on every enqueue or dequeue. While the right solution is in general to avoid doing that, we wanted to fix this, and as it turns out, the fix was relatively straightforward, such that we could have our performance cake and eat it, too. The results are very obvious in the following benchmark.

private ConcurrentQueue<int> _cq; [GlobalSetup] public void Setup() { _cq = new ConcurrentQueue<int>(); for (int i = 0; i < 100; i++) { _cq.Enqueue(i); } } [Benchmark] public void EnqueueCountDequeue() { _cq.Enqueue(42); _ = _cq.Count; _cq.TryDequeue(out _); }

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated EnqueueCountDequeue netcoreapp2.1 708.48 ns 23.8638 ns 21.1546 ns 1.00 0.1669 0.0830 0.0010 704 B EnqueueCountDequeue netcoreapp3.0 22.79 ns 0.4471 ns 0.4182 ns 0.03 – – – –

ImmutableDictionary<TKey, TValue> also got some attention. A customer reported that they’d compared ImmutableDictionary<TKey, TValue> and Dictionary<TKey, TValue> and found the former to be measurably slower for lookups. This is to be expected, as the types use very different data structures, with ImmutableDictionary optimized for being able to inexpensively create a copy of the dictionary with a mutation, something that’s quite expensive to do with Dictionary ; the trade-off is that it ends up being slower for lookups. Still, it caused us to take a look at the costs involved in ImmutableDictionary lookups, and PR dotnet/corefx#35759 includes several tweaks to improve it, changing a recursive call to be non-recursive and inlinable and avoiding some unnecessary struct wrapping. While this doesn’t make ImmutableDictionary and Dictionary lookups equivalent, it does improve ImmutableDictionary measurably, especially when it contains just a few elements.

private ImmutableDictionary<int, int> _hundredInts; [GlobalSetup] public void Setup() { _hundredInts = ImmutableDictionary.Create<int, int>(); for (int i = 0; i < 100; i++) { _hundredInts = _hundredInts.Add(i, i); } } [Benchmark] public int Lookup() { int count = 0; { for (int i = 0; i < 100; i++) { for (int j = 0; j < 100; j++) { if (_hundredInts.TryGetValue(j, out _)) { count++; } } } } return count; }

Method Toolchain Mean Error StdDev Median Ratio RatioSD Lookup netcoreapp2.1 303.9 us 7.271 us 15.016 us 297.8 us 1.00 0.00 Lookup netcoreapp3.0 174.5 us 3.360 us 2.806 us 174.5 us 0.57 0.03

Another collection that’s seen measurable improvements in .NET Core 3.0 is

BitArray . Lots of operations, including construction, were optimized in PR dotnet/corefx#33367.

private byte[] _bytes = Enumerable.Range(0, 100).Select(i => (byte)i).ToArray(); [Benchmark] public BitArray BitArrayCtor() => new BitArray(_bytes);

Method Toolchain Mean Error StdDev Median Ratio RatioSD BitArrayCtor netcoreapp2.1 82.28 ns 2.601 ns 7.546 ns 77.89 ns 1.00 0.00 BitArrayCtor netcoreapp3.0 46.87 ns 2.738 ns 8.030 ns 44.63 ns 0.57 0.10

Core operations like

Set and Get were further improved in PR dotnet/corefx#35364 from @omariom by streamlining the relevant methods and making them inlineable

private BitArray _ba = new BitArray(Enumerable.Range(0, 1000).Select(i => i % 2 == 0).ToArray()); [Benchmark] public void GetSet() { BitArray ba = _ba; for (int i = 0; i < 1000; i++) { ba.Set(i, !ba.Get(i)); } }

Method Toolchain Mean Error StdDev Ratio GetSet netcoreapp2.1 6.497 us 0.0854 us 0.0713 us 1.00 GetSet netcoreapp3.0 2.049 us 0.0233 us 0.0218 us 0.32

while other operations like

Or , And , and Xor were vectorized in PR dotnet/corefx#33781. This benchmark highlights some of the wins.

private BitArray _ba1 = new BitArray(Enumerable.Range(0, 1000).Select(i => i % 2 == 0).ToArray()); private BitArray _ba2 = new BitArray(Enumerable.Range(0, 1000).Select(i => i % 2 == 1).ToArray()); [Benchmark] public void Xor() => _ba1.Xor(_ba2);

Method Toolchain Mean Error StdDev Ratio Xor netcoreapp2.1 28.57 ns 0.4086 ns 0.3822 ns 1.00 Xor netcoreapp3.0 10.92 ns 0.0924 ns 0.0772 ns 0.38

Another example:

SortedSet<T> . PR dotnet/corefx#30921 from @acerbusace tweaks how GetViewBetween changes how counts of the overall set and subset are managed, resulting in a nice performance boost.

private SortedSet<int> _set = new SortedSet<int>(Enumerable.Range(0, 1000)); [Benchmark] public int EnumerateViewBetween() { int count = 0; foreach (int item in _set.GetViewBetween(100, 200)) count++; return count; }

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated EnumerateViewBetween netcoreapp2.1 5.117 us 0.0590 us 0.0552 us 1.00 0.2518 – – 544 B EnumerateViewBetween netcoreapp3.0 2.510 us 0.0307 us 0.0287 us 0.49 0.1373 – – 288 B

Comparers have also seen some nice improvements in .NET Core 3.0. For example, PR

dotnet/coreclr#21604 overhauled how comparers for enums are implemented in the runtime, borrowing the approach used in CoreRT. It’s often the case that performance optimizations involve adding code; this is one of those fortuitous cases where the better approach is not only faster, it’s also simpler and smaller.

private enum ExampleEnum : byte { A, B } [Benchmark] public void CompareEnums() { var comparer = Comparer<ExampleEnum>.Default; for (int i = 0; i < 100_000_000; i++) { comparer.Compare(ExampleEnum.A, ExampleEnum.B); } }

Method Toolchain Mean Error StdDev Ratio RatioSD CompareEnums netcoreapp2.1 239.5 ms 10.130 ms 10.403 ms 1.00 0.00 CompareEnums netcoreapp3.0 131.7 ms 2.479 ms 2.319 ms 0.55 0.03

Networking

From the Kestrel web server running on System.Net.Sockets and System.Net.Security to applications accessing web services via HttpClient , System.Net now more than ever is critical path for many applications. It received a lot of attention in .NET Core 2.1, and continues to in .NET Core 3.0. Let’s start with HttpClient . One improvement made in PR dotnet/corefx#32820 was around how buffering is handled, and in particular better respecting larger buffer size requests made as part of copying the response data when a content length was provided by the server. On a fast connection and with a large response body (such as the 10MB in this example), this can make a sizeable difference in throughput due to reduced syscalls to transfer data.

private HttpClient _client = new HttpClient(); private Socket _listener; private Uri _uri; [GlobalSetup] public void Setup() { _listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); _listener.Bind(new IPEndPoint(IPAddress.Loopback, 0)); _listener.Listen(int.MaxValue); var ep = (IPEndPoint)_listener.LocalEndPoint; _uri = new Uri($"http://{ep.Address}:{ep.Port}"); Task.Run(async () => { while (true) { Socket s = await _listener.AcceptAsync(); var ignored = Task.Run(async () => { ReadOnlyMemory<byte> headers = Encoding.ASCII.GetBytes("HTTP/1.1 200 OK\r

Content-Length: 10485760\r

\r

"); ReadOnlyMemory<byte> data = new byte[10*1024*1024]; // 10485760 using (var serverStream = new NetworkStream(s, true)) using (var reader = new StreamReader(serverStream)) { while (true) { while (!string.IsNullOrEmpty(await reader.ReadLineAsync())) ; await s.SendAsync(headers, SocketFlags.None); await s.SendAsync(data, SocketFlags.None); } } }); } }); } [Benchmark] public async Task HttpDownload() { using (HttpResponseMessage r = await _client.GetAsync(_uri, HttpCompletionOption.ResponseHeadersRead)) using (Stream s = await r.Content.ReadAsStreamAsync()) { await s.CopyToAsync(Stream.Null); } }

Method Toolchain Mean Error StdDev Ratio RatioSD HttpDownload netcoreapp2.1 8.792 ms 0.1833 ms 0.3397 ms 1.00 0.00 HttpDownload netcoreapp3.0 4.615 ms 0.0356 ms 0.0278 ms 0.52 0.02

Now consider

SslStream . Previous releases saw work done to make reads and writes on SslStream much more efficient, but additional work was done in .NET Core 3.0 as part of PRs dotnet/corefx#35091 and dotnet/corefx#35209 (and dotnet/corefx#35367 on Unix) to make initiating the connection more efficient, in particular in terms of allocations.

private NetworkStream _client; private NetworkStream _server; private static X509Certificate2 s_cert = GetServerCertificate(); private static X509Certificate2 GetServerCertificate() { var certCollection = new X509Certificate2Collection(); byte[] testCertBytes = Convert.FromBase64String(@"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"); certCollection.Import(testCertBytes, "testcertificate", X509KeyStorageFlags.DefaultKeySet); return certCollection.Cast<X509Certificate2>().First(c => c.HasPrivateKey); } [GlobalSetup] public void Setup() { using (var listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)) { listener.Bind(new IPEndPoint(IPAddress.Loopback, 0)); listener.Listen(1); var client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); client.Connect(listener.LocalEndPoint); Socket server = listener.Accept(); _client = new NetworkStream(client); _server = new NetworkStream(server); } } [Benchmark] public void SslConnect() { using (var sslClient = new SslStream(_client, true, delegate { return true; })) using (var sslServer = new SslStream(_server, true, delegate { return true; })) { Task t = sslServer.AuthenticateAsServerAsync(s_cert, false, SslProtocols.None, false); sslClient.AuthenticateAsClient("localhost", null, SslProtocols.None, false); t.Wait(); } }

Method Toolchain Mean Error StdDev Ratio RatioSD Gen 0 Gen 1 Gen 2 Allocated SslConnect netcoreapp2.1 1,151.7 us 34.85 us 102.76 us 1.00 0.00 5.8594 – – 9.82 KB SslConnect netcoreapp3.0 915.5 us 17.73 us 26.54 us 0.80 0.08 1.9531 – – 4.13 KB

In

System.Net.Sockets there’s another example of taking advantage of the IThreadPoolWorkItem interface discussed earlier. On Windows for asynchronous operations, we utilize “overlapped I/O”, utilizing threads from the I/O thread pool to execute continuations from socket operations; Windows queues I/O completion packets that these I/O pool threads then process, including invoking the continuations. On Unix, however, the mechanism is very different. There’s no concept of “overlapped I/O” on Unix, and instead asynchrony in System.Net.Sockets is achieved by using epoll (or kqueues on macOS), with all of the sockets in the system registered with an epoll file descriptor, and then one thread monitoring that epoll for changes. Any time an asynchronous operation completes for a socket, the epoll is signaled and the thread blocking on it wakes up to process it. If that thread were to run the socket continuation action then and there, it would end up potentially running unbounded work that could stall every other socket’s handling indefinitely, and in the extreme case, deadlock. Instead, this thread queues a work item back to the thread pool and then immediately goes back to processing any other socket work. Prior to .NET Core 3.0, that queueing involved an allocation, which meant that every asynchronously completing socket operation on Unix involved at least one allocation. As of PR dotnet/corefx#32919, that number drops to zero, as a cached object already being used (and reused) to represent asynchronous operations was changed to also implement IThreadPoolWorkItem and be queueable directly to the thread pool. Other areas of System.Net have benefited from the efforts already alluded to previously, as well. For example, Dns.GetHostName used to use StringBuilder in its marshaling, but as of PR dotnet/corefx#29594 it no longer does.

[Benchmark] public string GetHostName() => Dns.GetHostName();

Method Toolchain Mean Error StdDev Ratio RatioSD Gen 0 Gen 1 Gen 2 Allocated GetHostName netcoreapp2.1 85.77 us 1.656 us 1.5489 us 1.00 0.00 0.4883 – – 1176 B GetHostName netcoreapp3.0 81.42 us 1.016 us 0.9503 us 0.95 0.02 – – – 48 B

And

IPAddress.HostToNetworkOrder/NetworkToHostOrder have benefiting indirectly from the intrinsics push that was mentioned previously. In .NET Core 2.1, BinaryPrimitives.ReverseEndianness was added with an optimized software implementation, and these IPAddress methods were rewritten as simple wrappers for ReverseEndianness . Now in .NET Core 3.0, PR dotnet/coreclr#18398 turned ReverseEndianness into a JIT intrinsic for which the JIT can emit a very efficient BSWAP instruction, with the resulting throughput improvements accruing to IPAddress as well.

private long _value = 1234567890123456789; [Benchmark] public long HostToNetworkOrder() => IPAddress.HostToNetworkOrder(_value);

Method Toolchain Mean Error StdDev Median Ratio RatioSD HostToNetworkOrder netcoreapp2.1 0.4986 ns 0.0398 ns 0.0408 ns 0.4758 ns 1.000 0.00 HostToNetworkOrder netcoreapp3.0 0.0043 ns 0.0090 ns 0.0076 ns 0.0000 ns 0.009 0.02

System.IO

Often going hand in hand with networking is compression, which has also seen some improvements in .NET Core 3.0. Most notably is that a key dependency was updated. On Unix, System.IO.Compression just uses the zlib library available on the machine, as it’s a standard part of most any distro/version. On Windows, however, zlib is generally nowhere to be found, and so it’s built and shipped as part of .NET Core on Windows. Rather than shipping the standard zlib, .NET Core includes a version modified by Intel with additional performance improvements not yet merged upstream. In .NET Core 3.0, we’ve sync’d to the latest available version of ZLib-Intel, version 1.2.11. This brings some very measurable performance improvements, in particular around decompression. There have also been compression-related improvements that take advantage of previous improvements elsewhere in .NET Core. For example, the synchronous Stream.CopyTo was originally non-virtual, but as gains were found by overriding the asynchronous CopyToAsync and specializing its implementation for particular concrete stream types, CopyTo was made virtual to enjoy similar improvements. PR dotnet/corefx#29751 capitalized on this to override CopyTo on DeflateStream , employing similar optimizations in the synchronous implementation as were employed in the asynchronous implementation, essentially entailing minimizing the interop costs with zlib.

private byte[] _compressed; [GlobalSetup] public void Setup() { var ms = new MemoryStream(); using (var ds = new DeflateStream(ms, CompressionLevel.Fastest)) { ds.Write(Enumerable.Range(0, 1_000_000).Select(i => (byte)i).ToArray(), 0, 1_000_000); } _compressed = ms.ToArray(); } [Benchmark] public void DeflateDecompress() { using (var ds = new DeflateStream(new MemoryStream(_compressed), CompressionMode.Decompress)) { ds.CopyTo(Stream.Null); } }

Method Toolchain Mean Error StdDev Ratio DeflateDecompress netcoreapp2.1 310.6 us 1.960 us 1.6367 us 1.00 DeflateDecompress netcoreapp3.0 144.9 us 1.050 us 0.9819 us 0.47

Improvements were also made to

BrotliStream (which as of .NET Core 3.0 is also used by HttpClient to automatically decompress Brotli-encoded content). Previously every new BrotliStream would also allocate a large buffer, but as of PR dotnet/corefx#35492, that buffer is pooled, as it is with DeflateStream (additionally, BrotliStream now as of PR dotnet/corefx#30135 overrides ReadByte and WriteByte to avoid allocations in the base implementation).

[Benchmark] public void BrotliWrite() { using (var bs = new BrotliStream(Stream.Null, CompressionLevel.Fastest)) { for (int i = 0; i < 1_000; i++) { bs.WriteByte((byte)i); } } }

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated BrotliWrite netcoreapp2.1 743.2 us 10.056 us 9.406 us 1.00 44.9219 – – 97680 B BrotliWrite netcoreapp3.0 575.5 us 9.181 us 8.588 us 0.77 – – – 136 B

Moving on from compression, it’s worth highlighting that formatting applies in more situations than just formatting individual primitives.

TextWriter , for example, has multiple methods for writing with format strings, e.g. public override void Write(string format, object arg0, arg1) . PR dotnet/coreclr#19235 improved on that for StreamWriter by providing specialized overrides that take a more efficient path that reduces allocation:

private StreamWriter _writer = new StreamWriter(Stream.Null); [Benchmark] public void StreamWriterFormat() => _writer.Write("Writing out a value: {0}", 42);

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated StreamWriterFormat netcoreapp2.1 207.4 ns 2.103 ns 1.864 ns 1.00 0.0455 – – 96 B StreamWriterFormat netcoreapp3.0 170.2 ns 1.800 ns 1.595 ns 0.82 0.0114 – – 24 B

As another example, PR

dotnet/coreclr#22102 from @TomerWeisberg improved the parsing performance of various primitive types on BinaryReader by special-casing the common situation where the BinaryReader wraps a MemoryStream . Or consider PR dotnet/corefx#30667 from @MarcoRossignoli, who added overrides to StringWriter for the Write{Line}{Async} methods that take a StringBuilder argument. StringWriter is just a wrapper around a StringBuilder , and StringBuilder knows how to append another StringBuilder to it, so these overrides on StringWriter can feed them right through.

private StringBuilder _underlying; private StringWriter _writer; private StringBuilder _sb; [GlobalSetup] public void Setup() { _underlying = new StringBuilder(); _writer = new StringWriter(_underlying); _sb = new StringBuilder("This is a test. This is only a test."); } [Benchmark] public void Write() { _underlying.Clear(); _writer.Write(_sb); }

Method Toolchain Mean Error StdDev Ratio Gen 0 Gen 1 Gen 2 Allocated Write netcoreapp2.1 30.15 ns 0.6065 ns 0.5673 ns 1.00 0.0495 – – 104 B Write netcoreapp3.0 18.57 ns 0.1513 ns 0.1416 ns 0.62 – – – –

System.IO.Pipelines is another IO-related library that’s received a lot of attention in .NET Core 3.0. Pipelines was introduced in .NET Core 2.1, and provides buffer-management as part of an I/O pipeline, used heavily by ASP.NET Core. A variety of PRs have gone into improving its performance. For example, PR dotnet/corefx#35171special-cases the common and default case where the Pool specified to be used by a Pipe is the default MemoryPool<byte>.Shared . Rather than go through MemoryPool<byte>.Shared in this case, the Pipe now bypasses it and goes to the underlying ArrayPool<byte>.Shared directly, which removes a layer of indirection but also the allocation of IMemoryOwner<byte> objects returned from MemoryPool<byte>.Rent . (Note that for this benchmark, since System.IO.Pipelines is part of a NuGet package rather than in the shared framework, I’ve added a Benchmark.NET config that specifies what package version to use with each run in order to show the improvements.)

// Run with: dotnet run -c Release -f netcoreapp2.1 --filter *Program* private sealed class Config : ManualConfig // also add [Config(typeof(Config))] to the Program class { public Config() { Add(Job.MediumRun.With(CsProjCoreToolchain.NetCoreApp21).WithNuGet("System.IO.Pipelines", "4.5.0").WithId("4.5.0")); Add(Job.MediumRun.With(CsProjCoreToolchain.NetCoreApp30).WithNuGet("System.IO.Pipelines", "4.6.0-preview5.19224.8").WithId("4.6.0-preview5.19224.8")); } } private readonly Pipe _pipe = new Pipe(); private byte[] _buffer = new byte[1024]; [Benchmark] public async Task ReadWrite() { var reader = _pipe.Reader; var writer = _pipe.Writer; for (int i = 0; i < 1000; i++) { ValueTask<ReadResult> vt = reader.ReadAsync(); await writer.WriteAsync(_buffer); ReadResult rr = await vt; reader.AdvanceTo(rr.Buffer.End); } }

Method Job NuGetReferences Toolchain Mean Error StdDev Gen 0 Gen 1 Gen 2 ReadWrite 4.5.0 System.IO.Pipelines 4.5.0 .NET Core 2.1 406.8 us 12.774 us 17.907 us 11.2305 – – ReadWrite 4.6.0-preview5.19224.8 System.IO.Pipelines 4.6.0-preview5.19224.8 .NET Core 3.0 324.6 us 3.208 us 4.702 us – – –

PR

dotnet/corefx#33658 from @benaadams allows Pipe to use the UnsafeQueueUserWorkItem boxing-related optimizations described earlier, PR dotnet/corefx#33755 avoids queueing unnecessary work items, PR dotnet/corefx#35939 tweaks the defaults used to better handle buffering in common cases, PR dotnet/corefx#35216 reduces the amount of slicing performed in various pipe operations, PR dotnet/corefx#35234 from @benaadams reduces the locking used in core operations, PR dotnet/corefx#35509 reduces argument validation (decreasing branching costs), PR dotnet/corefx#33000 focused on reducing costs associated with ReadOnlySequence<byte> that’s the main exchange type pipelines passes around, and PR dotnet/corefx#29837 further optimizes operations like GetSpan and Advance on the Pipe . The net result is to whittle away at already low CPU and allocation overheads.

// Run with: dotnet run -c Release -f netcoreapp2.1 --filter *Program* private sealed class Config : ManualConfig // also add [Config(typeof(Config))] to the Program class { public Config() { Add(Job.MediumRun.With(CsProjCoreToolchain.NetCoreApp21).WithNuGet("System.IO.Pipelines", "4.5.0").WithId("4.5.0")); Add(Job.MediumRun.With(CsProjCoreToolchain.NetCoreApp30).WithNuGet("System.IO.Pipelines", "4.6.0-preview5.19224.8").WithId("4.6.0-preview5.19224.8")); } } private readonly Pipe _pipe1 = new Pipe(); private readonly Pipe _pipe2 = new Pipe(); private byte[] _buffer = new byte[1024]; [GlobalSetup] public void Setup() { Task.Run(async () => { var reader = _pipe2.Reader; var writer = _pipe1.Writer; while (true) { ReadResult rr = await reader.ReadAsync(); foreach (ReadOnlyMemory<byte> mem in rr.Buffer) { await writer.WriteAsync(mem); } reader.AdvanceTo(rr.Buffer.End); } }); } [Benchmark] public async Task ReadWrite() { var reader = _pipe1.Reader; var writer = _pipe2.Writer; for (int i = 0; i < 1000; i++) { await writer.WriteAsync(_buffer); long count = 0; while (count < _buffer.Length) { ReadResult rr = await reader.ReadAsync(); count += rr.Buffer.Length; reader.AdvanceTo(rr.Buffer.End); } } }

Method Job NuGetReferences Toolchain Mean Error StdDev Gen 0 Gen 1 Gen 2 ReadWrite 4.5.0 System.IO.Pipelines 4.5.0 .NET Core 2.1 3.261 ms 0.0732 ms 0.1002 ms 46.8750 – – ReadWrite 4.6.0-preview5.19224.8 System.IO.Pipelines 4.6.0-preview5.19224.8 .NET Core 3.0 2.947 ms 0.1281 ms 0.1837 ms – – –

System.Console

Console isn’t something one normally thinks of as being performance-sensitive. However, there are two changes in this release that I think are worth calling attention to here. First, there is one area of Console about which we’ve heard numerous concerns related to performance, where the performance impact visibly impacts users. In particular, interactive console applications generally do a lot of manipulation of the cursor, which also entails asking where the cursor currently is. On Windows, both the setting and getting of the cursor are relatively fast operations, with P/Invoke calls made to functions exported from kernel32.dll. On Unix, things are more complicated. There’s no standard POSIX function for getting or setting a terminal’s cursor position. Instead, there’s a standard convention for interacting with the terminal via ANSI escape sequences. To set the cursor position, one writes a sequence of characters to stdout (e.g. “ESC [ 12 ; 34 H” to indicate 12th row, 34th column) and the terminal interprets that and reacts accordingly. Getting the cursor position is more of an ordeal. To get the current cursor position, an application writes to stdout a request (e.g. “ESC [ 6 n”), and in response the terminal writes back to the application’s stdin a response something like “ESC [ 12 ; 34 R”, to indicate the cursor is at the 12th row and 34th column. That response then needs to be read from stdin and parsed. So, in contrast to a fast interop call on Windows, on Unix we need to write, read, and parse text, and do so in a way that doesn’t cause problems with a user sitting at a keyboard using the app concurrently… not particularly cheap. When just getting the cursor position now and then, it’s not a big deal. But when getting it frequently, and when porting code originally written for Windows where the operation was so cheap the code being ported may not have been very frugal with how often it asked for the position (asking for it more than is really needed), this has resulted in visible performance problems. Thankfully, the issue has been addressed in .NET Core 3.0, by PR dotnet/corefx#36049 from @tmds. The change caches the current position and then manually handles updating that cached value based on user interactions, such as handling typing or resizing the terminal window. (Note that Benchmark.NET operates in a way that redirects 