Meet AMD’s Piledriver-Based FX Line-Up

Ed.: Originally, this story contained a page exploring resonant clock mesh technology, from Cyclos Semiconductor, which was expected to surface in AMD's Piledriver-based SoCs. Upon discussing this in greater depth with the company, however, "the timing of the products and the implementation of resonant clock mesh caused [the technology] to not be productized with "Piledriver" based processors." As such, we've removed that page to avoid any confusion.

As someone who reviews computer hardware, the challenges facing a business matter a lot less to me than the products it sells. We can all agree that the last year was pretty awful for AMD’s processor team, beginning with the power-hungry Bulldozer-based FX CPUs that slowly slid down in price over 12 months in response to a more compelling family of third-gen Core processors from Intel. But every delivery to my SoCal lab represents an opportunity. Chatter about mismanagement, layoffs, and a troubled past matter little in the evaluation of a new CPU. So, let's get down to business.

Sometimes it’s possible to predict the outcome of a story. Had AMD shipped an FX-8170 running 200 MHz faster than its former flagship, I would have guessed that it’d exhibit the same issues with lightly-threaded workloads, it would probably outperform a Core i5-2500K in more intensive tasks, but its power consumption would probably look pretty nasty compared to modern 77 W Ivy Bridge-based chips.

Instead, we have an FX-8350, which centers on the same Piledriver architecture as the Trinity-based APUs introduced less than one month ago. Experience tells us that, per core and per cycle, Piledriver can be as much as 15% faster than a Bulldozer-based design. Add to that the fact that FX-8350 operates at least 400 MHz faster than FX-8150. Oh, yeah. And Ivy Bridge only gave Intel’s line-up single-digit gains. There’s every chance that today’s performance comparison is going to be a lot more interesting than the overwhelmingly negative judgment passed on FX-8150 one year ago.

Meet The Piledriver-Based FX Family

In a faithful return to its Bulldozer approach, AMD sent out the fastest model in its new line-up for review, but is actually introducing eight-, six-, and four-core configurations. Of course, we know they all center on the Piledriver architecture, but the SoC itself is referred to as Vishera, and it’s still branded as FX.

AMD's Vishera processor die.

A complete Vishera processor measures 315 square millimeters and is composed of 1.2 billion transistors. Those are the exact same figures given for Zambezi, the previous-generation SoC based on AMD’s Bulldozer architecture. Whatever alterations the architects made—from ISA extensions to a larger L1 DTLB—surface area and transistor count don’t change enough to move the dial on those contextually-irrelevant but interesting-to-know-anyway specifications.

AMD's 2012 FX Family Core Count Base Clock Max. Turbo NB Clock TDP Price OPN FX-8350 8C / 8T 4.0 GHz 4.2 GHz 2200 MHz 125 W $195 FD8350FRW8KHK FX-8320 8C / 8T 3.5 GHz 4.0 GHz 2200 MHz 125 W $169 FD8320FRW8KHK FX-6300 6C / 6T 3.5 GHz 4.1 GHz 2000 MHz 95 W $132 FD6300WMW6KHK FX-4300 4C / 4T 3.8 GHz 4.0 GHz 2000 MHz 95 W $122 FD4300WMW4MHK

Two of the four SKUs boast eight integer cores, or four Piledriver modules, however you choose to label AMD’s compute units. The flagship, FX-8350, features a base clock rate of 4 GHz. Turbo Core technology is able to push that to 4.2 GHz in lightly-threaded workloads, though most of the chip’s speed-up undoubtedly comes from its default state. How much does Turbo Core really do for FX-8350? Not much. In iTunes, our single-threaded benchmark finishes three seconds faster with the feature on.

An FX-8320 drops the base clock rate to 3.5 GHz, though Turbo Core pushes that to 4 GHz under defined thermal limits (a 500 MHz speed-up is likely more meaningful to FX-8320). Both eight-core models include 8 MB of L2 cache (split into one shared 2 MB slice per module) and 8 MB of L3 cache (shared between all four of the SoC’s modules). AMD is suggesting a $195 price tag on FX-8350 and a $169 price on FX-8320.

FX-6300 comes equipped with three active modules (six cores) and drops pricing all the way to $132. A 3.5 GHz base clock rate helps take advantage of the architecture’s strengths in threaded apps, while a 4.1 GHz peak Turbo Core setting tries to compensate for lackluster single-threaded speed. Like the four-module parts, FX-6300 exposes 2 MB of shared L2 per module (totaling 6 MB in this case) and a shared 8 MB L3 cache. Fewer active resources (along with a slightly slower 2 GHz northbridge clock) allow FX-6300 to fit within a 95 W thermal ceiling, down from the 125 W limit imposed by both FX-83x0 processors.

A lone dual-module CPU, FX-4300, is also rated for 95 W. Its base 3.8 GHz clock rate is sped up to 4 GHz in lightly-threaded apps, and a 2 GHz northbridge frequency matches the FX-6300. A drop to 4 MB of shared L3, however, and a price tag just $10 under the triple-module chip will likely encourage most folks to spend the extra $10 bucks.

Although AMD’s architecture doesn’t seem particularly bandwidth-starved, Vishera’s dual-channel DDR3 memory controller officially supports 1866 MT/s data rates. Frankly, we’d rather use lower-latency 1600 MT/s modules to maximize value, particularly since our results show that you don't gain any performance (outside of Sandra 2013 Beta) after spending more on faster memory.

The entire FX line-up also features an unlocked ratio multiplier, which serves to simplify overclocking. Is Vishera scalable enough to make tuning worthwhile? What do you think about 5.125 GHz using a closed-loop liquid cooler?