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

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Message-ID: <Z7VrADfrrPB7GtfX@BLRRASHENOY1.amd.com>
Date: Wed, 19 Feb 2025 10:54:16 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Mario Limonciello <superm1@...nel.org>
Cc: Perry Yuan <perry.yuan@....com>,
	Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>,
	"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

Hello Mario,


On Mon, Feb 17, 2025 at 04:06:50PM -0600, 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);
>  	}

You can also remove the tracing code from amd_pstate_epp_reenable(), i.e,

	if (trace_amd_pstate_epp_perf_enabled()) {
		trace_amd_pstate_epp_perf(cpudata->cpu, cpudata->highest_perf,
					  cpudata->epp_cached,
					  FIELD_GET(AMD_CPPC_MIN_PERF_MASK, cpudata->cppc_req_cached),
					  max_perf, policy->boost_enabled);
	}

Since amd_pstate_epp_update_limit() also has the the tracing code.

The patch looks good to me otherwise.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>

-- 
Thanks and Regards
gautham.



>  
> -	return amd_pstate_update_perf(cpudata, 0, 0, max_perf, cpudata->epp_cached, false);
> +	return amd_pstate_epp_update_limit(policy);
>  }
>  
>  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;
>  
> -- 
> 2.43.0
>