linux-kernel - Re: [PATCH V3 2/3] cpufreq: intel_pstate: Migrate away from ->stop

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Date:   Fri, 18 Jun 2021 14:00:54 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dirk Brandewie <dirk.brandewie@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 2/3] cpufreq: intel_pstate: Migrate away from
 ->stop_cpu() callback

On Fri, Jun 18, 2021 at 5:22 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> commit 367dc4aa932b ("cpufreq: Add stop CPU callback to cpufreq_driver
> interface") added the stop_cpu() callback to allow the drivers to do
> clean up before the CPU is completely down and its state can't be
> modified.
>
> At that time the CPU hotplug framework used to call the cpufreq core's
> registered notifier for different events like CPU_DOWN_PREPARE and
> CPU_POST_DEAD. The stop_cpu() callback was called during the
> CPU_DOWN_PREPARE event.
>
> This is no longer the case, cpuhp_cpufreq_offline() is called only once
> by the CPU hotplug core now and we don't really need to separately
> call stop_cpu() for cpufreq drivers.
>
> Migrate to using the exit() and offline() callbacks instead of
> stop_cpu().
>
> We need to clear util hook from both the callbacks, exit() and
> offline(), since it is possible that only exit() gets called sometimes
> (specially on errors) or both get called at other times.
> intel_pstate_clear_update_util_hook() anyway have enough protection in
> place if it gets called a second time and will return early then.
>
> Cc: Dirk Brandewie <dirk.brandewie@...il.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> V2->V3:
> - Update intel_pstate_cpu_offline() as well.
> - Improved commit log.
>
>  drivers/cpufreq/intel_pstate.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 0e69dffd5a76..8f8a2d9d7daa 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -2335,6 +2335,8 @@ static int intel_pstate_cpu_offline(struct cpufreq_policy *policy)
>
>         pr_debug("CPU %d going offline\n", cpu->cpu);
>
> +       intel_pstate_clear_update_util_hook(policy->cpu);
> +
>         if (cpu->suspended)
>                 return 0;
>
> @@ -2374,17 +2376,12 @@ static int intel_pstate_cpu_online(struct cpufreq_policy *policy)
>         return 0;
>  }
>
> -static void intel_pstate_stop_cpu(struct cpufreq_policy *policy)
> -{
> -       pr_debug("CPU %d stopping\n", policy->cpu);
> -
> -       intel_pstate_clear_update_util_hook(policy->cpu);
> -}
> -
>  static int intel_pstate_cpu_exit(struct cpufreq_policy *policy)
>  {
>         pr_debug("CPU %d exiting\n", policy->cpu);
>
> +       intel_pstate_clear_update_util_hook(policy->cpu);

This change is not needed now, because ->offline always runs before
->exit if present.

> +
>         policy->fast_switch_possible = false;
>
>         return 0;
> @@ -2451,7 +2448,6 @@ static struct cpufreq_driver intel_pstate = {
>         .resume         = intel_pstate_resume,
>         .init           = intel_pstate_cpu_init,
>         .exit           = intel_pstate_cpu_exit,
> -       .stop_cpu       = intel_pstate_stop_cpu,
>         .offline        = intel_pstate_cpu_offline,
>         .online         = intel_pstate_cpu_online,
>         .update_limits  = intel_pstate_update_limits,
> --
> 2.31.1.272.g89b43f80a514
>