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

Meng, Li (Jassmine)
2024-02-20T07:23:11Z

[AMD Official Use Only - General]

Hi Lucas:

> -----Original Message-----
> From: Lucas Lee Jing Yi <lucasleeeeeeeee@gmail.com>
> Sent: Monday, February 19, 2024 12:11 AM
> To: rafael@kernel.org
> Cc: Yuan, Perry <Perry.Yuan@amd.com>; Du, Xiaojian
> <Xiaojian.Du@amd.com>; Deucher, Alexander
> <Alexander.Deucher@amd.com>; bp@alien8.de; Sharma, Deepak
> <Deepak.Sharma@amd.com>; Meng, Li (Jassmine) <Li.Meng@amd.com>;
> linux-acpi@vger.kernel.org; linux-kernel@vger.kernel.org; linux-
> kselftest@vger.kernel.org; linux-pm@vger.kernel.org; Limonciello, Mario
> <Mario.Limonciello@amd.com>; Fontenot, Nathan
> <Nathan.Fontenot@amd.com>; oleksandr@natalenko.name;
> rafael.j.wysocki@intel.com; Huang, Ray <Ray.Huang@amd.com>; Huang,
> Shimmer <Shimmer.Huang@amd.com>; skhan@linuxfoundation.org;
> viresh.kumar@linaro.org; x86@kernel.org; Lucas Lee Jing Yi
> <lucasleeeeeeeee@gmail.com>
> Subject: [PATCH] [PATCH] amd_pstate: fix erroneous highest_perf value on
> some CPUs
>
> Caution: This message originated from an External Source. Use proper
> caution when opening attachments, clicking links, or responding.
>
>
> 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);
> --
> 2.43.2
[Meng, Li (Jassmine)]
Reviewed-by: Li Meng < li.meng@amd.com>