RE: [RFC PATCH 6.1.y 0/1] cpufreq: amd-pstate: Enable CPU boost in passive and guided modes

Yuan, Perry
2024-10-25T03:23:20Z

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Nabil S. Alramli <dev@nalramli.com>
> Sent: Friday, October 25, 2024 9:05 AM
> To: stable@vger.kernel.org
> Cc: nalramli@fastly.com; jdamato@fastly.com; khubert@fastly.com; Yuan, Perry
> <Perry.Yuan@amd.com>; Meng, Li (Jassmine) <Li.Meng@amd.com>; Huang, Ray
> <Ray.Huang@amd.com>; rafael@kernel.org; viresh.kumar@linaro.org; linux-
> pm@vger.kernel.org; linux-kernel@vger.kernel.org; Nabil S. Alramli
> <dev@nalramli.com>
> Subject: [RFC PATCH 6.1.y 0/1] cpufreq: amd-pstate: Enable CPU boost in passive
> and guided modes
>
> Greetings,
>
> This is a RFC for a maintenance patch to an issue in the amd_pstate driver where
> CPU frequency cannot be boosted in passive or guided modes. Without this patch,
> AMD machines using stable kernels are unable to get their CPU frequency boosted,
> which is a significant performance issue.
>
> For example, on a host that has AMD EPYC 7662 64-Core processor without this
> patch running at full CPU load:
>
> $ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \
> do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \
> sort | uniq -c
>
> 128 2.0 GHz
>
> And with this patch:
>
> $ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \
> do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \
> sort | uniq -c
>
> 128 3.3 GHz
>
> I am not sure what the correct process is for submitting patches which affect only
> stable trees but not the current code base, and do not apply to the current tree. As
> such, I am submitting this directly to stable@, but please let me know if I should be
> submitting this elsewhere.
>
> The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq:
> amd-pstate: Fix initial highest_perf value"), and exists in stable kernels up until
> v6.6.51.
>
> In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate:
> Enable amd-pstate preferred core support"), was introduced which significantly
> refactored the code. This commit cannot be ported back on its own, and would
> require reviewing and cherry picking at least a few dozen of commits in cpufreq,
> amd-pstate, ACPI, CPPC.
>
> This means kernels v6.1 up until v6.6.51 are affected by this significant
> performance issue, and cannot be easily remediated.
>
> Thank you for your attention and I look forward to your response in regards to what
> the best way to proceed is for getting this important performance fix merged.
>
> Best Regards,
>
> Nabil S. Alramli (1):
> cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
>
> drivers/cpufreq/amd-pstate.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> --
> 2.35.1

Add Mario and Gautham for any help.

Perry.