linux-kernel - Re: [PATCH v2] cpufreq: intel_pstate: set stale CPU frequency to minimum

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Date:   Tue, 22 Aug 2023 13:46:04 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, yang.jie@...ux.intel.com
Subject: Re: [PATCH v2] cpufreq: intel_pstate: set stale CPU frequency to minimum

On Sun, Aug 20, 2023 at 10:46 PM Doug Smythies <dsmythies@...us.net> wrote:
>
> The intel_pstate CPU frequency scaling driver does not
> use policy->cur and it is 0.
> When the CPU frequency is outdated arch_freq_get_on_cpu()
> will default to the nominal clock frequency when its call to
> cpufreq_quick_getpolicy_cur returns the never updated 0.
> Thus, the listed frequency might be outside of currently
> set limits. Some users are complaining about the high
> reported frequency, albeit stale, when their system is
> idle and/or it is above the reduced maximum they have set.
>
> This patch will maintain policy_cur for the intel_pstate
> driver at the current minimum CPU frequency.
>
> Reported-by: Yang Jie <yang.jie@...ux.intel.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217597
> Signed-off-by: Doug Smythies <dsmythies@...us.net>
> ---
>
> v1 -> v2:
>    * v1 was a completely different approach, programming around
>      the issue rather than fixing it at the source.
>      reference:
>      https://patchwork.kernel.org/project/linux-pm/patch/006901d9be8c$f4439930$dccacb90$@telus.net/
>    * v2 does not fix an issue with the intel_cpufreq CPU scaling
>      driver (A.K.A. the intel_pstate driver in passive mode) and
>      the schedutil CPU frequency scaling governor when HWP is enabled
>      where limit changes are not reflected in the stale listed frequencies.
>      A fix for that will be some future patch.
>
> ---
>  drivers/cpufreq/intel_pstate.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 8ca2bce4341a..08284dee583a 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -2609,6 +2609,11 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
>                         intel_pstate_clear_update_util_hook(policy->cpu);
>                 intel_pstate_hwp_set(policy->cpu);
>         }
> +       /* policy current is never updated with the intel_pstate driver
> +        * but it is used as a stale frequency value. So, keep it within
> +        * limits.
> +        */
> +       policy->cur = policy->min;
>
>         mutex_unlock(&intel_pstate_limits_lock);
>
> --

Applied as 6.6 material, with some mailer-induced white space damage
fixed and the new comment adjusted to the kernel coding style.

Thanks!