linux-kernel - Re: [PATCH v4 4/7] cpufreq: amd-pstate: fix the MSR highest perf will be reset issue while cpb boost off

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Date: Thu, 14 Mar 2024 15:32:27 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Perry Yuan <perry.yuan@....com>
Cc: rafael.j.wysocki@...el.com, Mario.Limonciello@....com,
	viresh.kumar@...aro.org, Ray.Huang@....com, Borislav.Petkov@....com,
	Alexander.Deucher@....com, Xinmei.Huang@....com,
	Xiaojian.Du@....com, Li.Meng@....com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/7] cpufreq: amd-pstate: fix the MSR highest perf
 will be reset issue while cpb boost off

Hello Perry,

On Wed, Mar 13, 2024 at 06:04:41PM +0800, Perry Yuan wrote:
> From: Perry Yuan <Perry.Yuan@....com>
> 
> Select the min perf to fix the highest perf value while update pstate
> CPPC request MSR register, here we need to limit the max perf value when
> CPU boost is disabled in case of that highest perf value in the MSR will be
> reset to original highest perf value which cause the BOOST control
> failed.

>From the code in this patch, what you are trying to do is limit the
max_perf value to the minimum of the highest_perf and nominal_perf
when boost is disabled. A question : Why not unconditionally set the
max_perf to the nominal_perf ?

--
Thanks and Regards
gautham.

> 
> Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> ---
>  drivers/cpufreq/amd-pstate.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 0965fbf660dd..d7afbded6e3d 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -440,6 +440,7 @@ static void amd_pstate_update(struct amd_cpudata *cpudata, u32 min_perf,
>  			      u32 des_perf, u32 max_perf, bool fast_switch, int gov_flags)
>  {
>  	u64 prev = READ_ONCE(cpudata->cppc_req_cached);
> +	u32 nominal_perf = READ_ONCE(cpudata->nominal_perf);
>  	u64 value = prev;
>  
>  	min_perf = clamp_t(unsigned long, min_perf, cpudata->min_limit_perf,
> @@ -459,6 +460,10 @@ static void amd_pstate_update(struct amd_cpudata *cpudata, u32 min_perf,
>  	value &= ~AMD_CPPC_DES_PERF(~0L);
>  	value |= AMD_CPPC_DES_PERF(des_perf);
>  
> +	/* limit the max perf when core performance boost feature is disabled */
> +	if (!amd_pstate_global_params.cpb_boost)
> +		max_perf = min_t(unsigned long, nominal_perf, max_perf);
> +
>  	value &= ~AMD_CPPC_MAX_PERF(~0L);
>  	value |= AMD_CPPC_MAX_PERF(max_perf);
>  
> -- 
> 2.34.1
>