Re: [PATCH] cpufreq/amd-pstate: Fix MinPerf MSR value for performance policy

[Mario Limonciello <mario.limonciello@amd.com>]

On 1/7/26 3:19 PM, Juan Martinez wrote:
> When the CPU frequency policy is set to CPUFREQ_POLICY_PERFORMANCE
> (which occurs when EPP hint is set to "performance"), the driver
> incorrectly sets the MinPerf field in CPPC request MSR to nominal_perf
> instead of lowest_nonlinear_perf.
> 
> According to the AMD architectural programmer's manual volume 2 [1],
> in section "17.6.4.1 CPPC_CAPABILITY_1", lowest_nonlinear_perf represents
> the most energy efficient performance level (in terms of performance per
> watt). The MinPerf field should be set to this value even in performance
> mode to maintain proper power/performance characteristics.
> 
> This fixes a regression introduced by commit 0c411b39e4f4c ("amd-pstate: Set
> min_perf to nominal_perf for active mode performance gov"), which correctly
> identified that highest_perf was too high but chose nominal_perf as an
> intermediate value instead of lowest_nonlinear_perf.
> 
> The fix changes amd_pstate_update_min_max_limit() to use lowest_nonlinear_perf
> instead of nominal_perf when the policy is CPUFREQ_POLICY_PERFORMANCE.
> 
> [1] https://docs.amd.com/v/u/en-US/24593_3.43
>      AMD64 Architecture Programmer's Manual Volume 2: System Programming
>      Section 17.6.4.1 CPPC_CAPABILITY_1
>      (Referenced in commit 5d9a354cf839a)
> 
> Fixes: 0c411b39e4f4c ("amd-pstate: Set min_perf to nominal_perf for active mode performance gov")
> Tested-by: Kaushik Reddy S <kaushik.reddys@amd.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Juan Martinez <juan.martinez@amd.com>

I think this change is reasonable, but I'd like to get Gautham's 
comments as the original author of 0c411b39e4f4c.

> ---
>   drivers/cpufreq/amd-pstate.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index e4f1933dd7d47..de0bb5b325502 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -634,8 +634,8 @@ static void amd_pstate_update_min_max_limit(struct cpufreq_policy *policy)
>   	WRITE_ONCE(cpudata->max_limit_freq, policy->max);
>   
>   	if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE) {
> -		perf.min_limit_perf = min(perf.nominal_perf, perf.max_limit_perf);
> -		WRITE_ONCE(cpudata->min_limit_freq, min(cpudata->nominal_freq, cpudata->max_limit_freq));
> +		perf.min_limit_perf = min(perf.lowest_nonlinear_perf, perf.max_limit_perf);
> +		WRITE_ONCE(cpudata->min_limit_freq, min(cpudata->lowest_nonlinear_freq, cpudata->max_limit_freq));
>   	} else {
>   		perf.min_limit_perf = freq_to_perf(perf, cpudata->nominal_freq, policy->min);
>   		WRITE_ONCE(cpudata->min_limit_freq, policy->min);