linux-kernel - Re: [PATCH v3 01/18] cpufreq/amd-pstate: Invalidate cppc_req

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Message-ID: <66c37c15-e655-4c1e-ba5f-70307a0c8b1a@amd.com>
Date: Wed, 19 Feb 2025 11:42:51 +0530
From: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
To: Mario Limonciello <superm1@...nel.org>,
 "Gautham R . Shenoy" <gautham.shenoy@....com>,
 Perry Yuan <perry.yuan@....com>
Cc: "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
 <linux-kernel@...r.kernel.org>,
 "open list:CPU FREQUENCY SCALING FRAMEWORK" <linux-pm@...r.kernel.org>,
 Mario Limonciello <mario.limonciello@....com>,
 Miroslav Pavleski <miroslav@...leski.net>
Subject: Re: [PATCH v3 01/18] cpufreq/amd-pstate: Invalidate cppc_req_cached
 during suspend

On 2/18/2025 3:36 AM, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@....com>
> 
> During resume it's possible the firmware didn't restore the CPPC request MSR
> but the kernel thinks the values line up. This leads to incorrect performance
> after resume from suspend.
> 
> To fix the issue invalidate the cached value at suspend. During resume use
> the saved values programmed as cached limits.
> 
> Reported-by: Miroslav Pavleski <miroslav@...leski.net>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217931
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  drivers/cpufreq/amd-pstate.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index f425fb7ec77d7..12fb63169a24c 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1611,7 +1611,7 @@ static int amd_pstate_epp_reenable(struct cpufreq_policy *policy)
>  					  max_perf, policy->boost_enabled);
>  	}
>  
> -	return amd_pstate_update_perf(cpudata, 0, 0, max_perf, cpudata->epp_cached, false);
> +	return amd_pstate_epp_update_limit(policy);

Can we also add the check "if (policy->min != cpudata->min_limit_freq || policy->max != cpudata->max_limit_freq)"
in "amd_pstate_epp_update_limit()" before calling "amd_pstate_update_min_max_limit()". I think it would help in 
avoiding some unnecessary calls to the update_min_max_limit() function.

Patch looks good to me otherwise.

Thanks,
Dhananjay

>  }
>  
>  static int amd_pstate_epp_cpu_online(struct cpufreq_policy *policy)
> @@ -1660,6 +1660,9 @@ static int amd_pstate_epp_suspend(struct cpufreq_policy *policy)
>  	if (cppc_state != AMD_PSTATE_ACTIVE)
>  		return 0;
>  
> +	/* invalidate to ensure it's rewritten during resume */
> +	cpudata->cppc_req_cached = 0;
> +
>  	/* set this flag to avoid setting core offline*/
>  	cpudata->suspended = true;
>