This morning I delivered the initial Linux processor benchmarks of the Core i7 8700K and Core i5 8400 for the just-launched "Coffee Lake" desktop processors. With these Intel "Gen 8" processors, the integrated "HD Graphics" from Kabylake have been rebranded to "UHD Graphics". While there wasn't any real changes architecturally to the graphics hardware, right now the Linux support isn't quite out-of-the-box.

When first powering on the i5-8400 and i7-8700K configurations, I was surprised to see the Intel DRM driver not working... This was connected to a 4K display and the mode-setting to it didn't happen with being stuck on the efifb driver. Of course, LLVMpipe was at play to lead to a sluggish experience...

At first I didn't realize what was going on since the Coffee Lake PCI IDs are present in all of the components of the Intel Linux graphics driver stack, I was using Ubuntu 17.10 with its stock Linux 4.13 that is quite new, and these Coffee Lake graphics that are essentially rebranded Gen 9 GT2 graphics hardware from Kabylake were not working. When grep'ing dmesg for i915 (Intel's DRM driver name), there were just some audio references and a line about alpha support. Initially off the top of my head I figured it was some new tunable having something to do with alpha compositing or the like given all the new display work happening within the Intel space.

Well, after then searching the contents of dmesg after finding the time today, I realize the i915.alpha_support option is actually for alpha/preliminary hardware support... Previously this was the "i915.preliminary_hw_support=1" switch for enabling early hardware support, but seems to have quietly been renamed to just "alpha". And if you are grep'ing dmesg looking for the i915 hints of what's going wrong, the actual line mentioning it's to do with alpha hardware support doesn't have any references. So just a silly little thing to be aware of if you plan on being an early Coffee Lake customer.

When booting the Ubuntu 17.10 stock kernel with i915.alpha_support=1, 4K was working, OpenGL acceleration present, and Vulkan also working... I have yet to run into any Coffeelake graphics issues with the Core i5 8400 or Core i7 8700K yet. So I'm quite surprised Intel developers are still hiding this Coffeelake support behind the "alpha_support" flag consider these CPUs are now shipping, the Linux 4.13 stable still has it marked as stable, Linux 4.14 Git still requires the alpha flag for Coffee Lake, and even the current DRM-Next code still requires this be set. It's quite surprising especially with Coffeelake still being the Gen 9 / Kabylake-era graphics that have been well supported on Linux for effectively many months. I haven't seen any public references why it's this way or any responses from the upstream Intel Linux developers, but presumably just an oversight on their part.

I have spent most of my UHD Graphics 630 testing so far with the Core i7 8700K and paired with the Ubuntu 17.10 base I have tested its stock kernel as well as the vanilla/upstream Linux 4.13.0, Linux 4.14 Git, and DRM-Next kernels. Additionally, both with the Mesa 17.2 stable Vulkan/OpenGL driver stack as shipped by Ubuntu 17.10 and as well with Mesa 17.3-dev Git via the Padoka PPA as of earlier today.

Included in this article are a few different reference benchmarks of the Core i7 8700K graphics compared to other Intel integrated graphics hardware and other Linux graphics tests. Further Coffee Lake tests are being worked on for publishing in the coming days and weeks.