linux-kernel - Re: [PATCH v5 4/7] cpufreq: amd_pstate: fix wrong lowest perf fetch

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Message-ID: <87edxhim3j.fsf@stealth>
Date:   Mon, 15 Aug 2022 16:05:04 +0100
From:   Punit Agrawal <punit.agrawal@...edance.com>
To:     Perry Yuan <Perry.Yuan@....com>
Cc:     <rafael.j.wysocki@...el.com>, <ray.huang@....com>,
        <viresh.kumar@...aro.org>, <Deepak.Sharma@....com>,
        <Mario.Limonciello@....com>, <Nathan.Fontenot@....com>,
        <Alexander.Deucher@....com>, <Jinzhou.Su@....com>,
        <Shimmer.Huang@....com>, <Xiaojian.Du@....com>, <Li.Meng@....com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 4/7] cpufreq: amd_pstate: fix wrong lowest perf fetch

Hi Perry,

Perry Yuan <Perry.Yuan@....com> writes:

> Fix the wrong lowest perf value reading which is used for new
> des_perf calculation by governor requested, the incorrect min_perf will
> get incorrect des_perf to be set , that will cause the system frequency
> changing unexpectedly.
>
> Reviewed-by: Huang Rui <ray.huang@....com>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> Signed-off-by: Su Jinzhou <jinzhou.su@....com>
> ---
>  drivers/cpufreq/amd-pstate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 5cdef6638681..183cdd4ba00e 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -307,7 +307,7 @@ static int amd_pstate_target(struct cpufreq_policy *policy,
>  		return -ENODEV;
>  
>  	cap_perf = READ_ONCE(cpudata->highest_perf);
> -	min_perf = READ_ONCE(cpudata->lowest_nonlinear_perf);
> +	min_perf = READ_ONCE(cpudata->lowest_perf);
>  	max_perf = cap_perf;
>  
>  	freqs.old = policy->cur;

This looks to be a pretty big change (lowest nonlinear vs lowest). Does
the patch need to be backported to older kernels?