AMD + Valve Working On New Linux CPU Performance Scaling Design
Written by Michael Larabel in AMD on 2 August 2021 at 08:00 AM EDT. 25 Comments
AMD --
Along with other optimizations to benefit the Steam Deck, AMD and Valve have been jointly working on CPU frequency/power scaling improvements to enhance the Steam Play gaming experience on modern AMD platforms running Linux.

It's no secret that the ACPI CPUFreq driver code has at times been less than ideal on recent AMD processors with delivering less than expected performance/behavior with being slow to ramp up to a higher performance state or otherwise coming up short of disabling the power management functionality outright. AMD hasn't traditionally worked on the Linux CPU frequency scaling code as much as Intel does to their P-State scaling driver and other areas of power management at large.

AMD is ramping up efforts in these areas including around the Linux scheduler given their recent hiring spree while it now looks like thanks to the Steam Deck there is renewed interest in better optimizing the CPU frequency scaling under Linux.

AMD and Valve have been working to improve the performance/power efficiency for modern AMD platforms running on Steam Play (Proton / Wine) and have spearheaded "[The ACPI CPUFreq driver] was not very performance/power efficiency for modern AMD platforms...a new CPU performance scaling design for AMD platform which has better performance per watt scaling on such as 3D game like Horizon Zero Dawn with VKD3D-Proton on Steam."

AMD will be presenting more about this effort next month at XDC. It's quite possible this new effort is focused on ACPI CPPC support with the previously proposed AMD_CPUFreq. Back when Zen 2 launched in 2019, AMD did post patches for their new CPUFreq driver that leveraged ACPI Collaborative Processor Performance Controls but the driver was never mainlined nor any further iterations of the patches posted. When inquiring about that work a few times since then, AMD has always said it's been basically due to resource constraints that it wasn't a focus at that time. Upstream kernel developers also voiced their preference to seeing AMD work to improve the generic ACPI CPPC CPUFreq driver code rather than having another vendor-specific solution. It's also possible AMD has been working on better improvements around the now-default Schedutil governor for scheduler utilization data in making CPU frequency scaling decisions.

In any case, we are excited to see the AMD+Valve power/performance scaling improvements come to Linux. The Steam Deck leverages a Zen 2 based custom APU. If it's indeed leveraging ACPI CPPC, these Linux AMD platform improvements should benefit all Zen 2 hardware and newer (Zen 1 and prior lacking CPPC).

Hopefully AMD and Valve continue cooperating about further Linux optimizations both for on the CPU and graphics side. Already on the graphics side in recent years Valve has been employing multiple developers to improve Mesa with a particular focus on the RADV Vulkan driver and their work on the ACO compiler back-end and much more for significantly boosting the open-source Radeon advantage for Linux gamers.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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