Re: [PATCH] [PATCH] amd_pstate: fix erroneous highest_perf value on some CPUs

Oleksandr Natalenko
2024-02-20T09:03:11Z

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Hello.

On neděle 18. února 2024 17:10:31 CET Lucas Lee Jing Yi wrote:
> On a Ryzen 7840HS the highest_perf value is 196, not 166 as AMD assumed.
> This leads to the advertised max clock speed to only be 4.35ghz instead of 5.14ghz , leading to a large degradation in performance.
>
> Fix the broken assumption and revert back to the old logic for getting highest_perf.
>
> TEST:
> Geekbench 6 Before Patch:
> Single Core: 2325 (-22%)!
> Multi Core: 11335 (-10%)
>
> Geekbench 6 AFTER Patch:
> Single Core: 2635
> Multi Core: 12487
>
> Signed-off-by: Lucas Lee Jing Yi <lucasleeeeeeeee@gmail.com>
> ---
> drivers/cpufreq/amd-pstate.c | 22 ++++++++++------------
> 1 file changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 08e112444c27..54df68773620 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -50,7 +50,6 @@
>
> #define AMD_PSTATE_TRANSITION_LATENCY 20000
> #define AMD_PSTATE_TRANSITION_DELAY 1000
> -#define AMD_PSTATE_PREFCORE_THRESHOLD 166
>
> /*
> * TODO: We need more time to fine tune processors with shared memory solution
> @@ -299,15 +298,12 @@ static int pstate_init_perf(struct amd_cpudata *cpudata)
> &cap1);
> if (ret)
> return ret;
> -
> - /* For platforms that do not support the preferred core feature, the
> - * highest_pef may be configured with 166 or 255, to avoid max frequency
> - * calculated wrongly. we take the AMD_CPPC_HIGHEST_PERF(cap1) value as
> - * the default max perf.
> +
> + /* Some CPUs have different highest_perf from others, it is safer
> + * to read it than to assume some erroneous value, leading to performance issues.
> */
> - if (cpudata->hw_prefcore)
> - highest_perf = AMD_PSTATE_PREFCORE_THRESHOLD;
> - else
> + highest_perf = amd_get_highest_perf();
> + if(highest_perf > AMD_CPPC_HIGHEST_PERF(cap1))
> highest_perf = AMD_CPPC_HIGHEST_PERF(cap1);
>
> WRITE_ONCE(cpudata->highest_perf, highest_perf);
> @@ -329,9 +325,11 @@ static int cppc_init_perf(struct amd_cpudata *cpudata)
> if (ret)
> return ret;
>
> - if (cpudata->hw_prefcore)
> - highest_perf = AMD_PSTATE_PREFCORE_THRESHOLD;
> - else
> + /* Some CPUs have different highest_perf from others, it is safer
> + * to read it than to assume some erroneous value, leading to performance issues.
> + */
> + highest_perf = amd_get_highest_perf();
> + if(highest_perf > cppc_perf.highest_perf)
> highest_perf = cppc_perf.highest_perf;
>
> WRITE_ONCE(cpudata->highest_perf, highest_perf);
>

Please pay attention to trailing whitespaces, adding whitespaces to blank lines, and whitespaces between `if` and opening `(`.

`scripts/checkpatch.pl` may help you with that.

Thank you.

--
Oleksandr Natalenko (post-factum)

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