Re: [PATCH v1] cpufreq: intel_pstate: Rearrange locking in hybrid_init_cpu_capacity_scaling()

[Rafael J. Wysocki]

On Thu, Nov 7, 2024 at 1:36 PM Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> Notice that hybrid_init_cpu_capacity_scaling() only needs to hold
> hybrid_capacity_lock around __hybrid_init_cpu_capacity_scaling()
> calls, so introduce a "locked" wrapper around the latter and call
> it from the former.  This allows to drop a local variable and a
> label that are not needed any more.
>
> Also, rename __hybrid_init_cpu_capacity_scaling() to
> __hybrid_refresh_cpu_capacity_scaling() for consistency.
>
> No intentional functional impact.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

This turns out to be fixing a locking issue in commit 929ebc93ccaa
("cpufreq: intel_pstate: Set asymmetric CPU capacity on hybrid
systems") which is related to this report:

https://lore.kernel.org/linux-pm/SJ1PR11MB6129EDBF22F8A90FC3A3EDC8B9582@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

so I'll need to update the changelog, but the patch itself need not be changed.

> ---
>
> This is on top of
>
> https://lore.kernel.org/linux-pm/12555220.O9o76ZdvQC@xxxxxxxxxxxxx/
>
> ---
>  drivers/cpufreq/intel_pstate.c |   35 ++++++++++++++++-------------------
>  1 file changed, 16 insertions(+), 19 deletions(-)
>
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -1028,26 +1028,29 @@ static void hybrid_update_cpu_capacity_s
>         }
>  }
>
> -static void __hybrid_init_cpu_capacity_scaling(void)
> +static void __hybrid_refresh_cpu_capacity_scaling(void)
>  {
>         hybrid_max_perf_cpu = NULL;
>         hybrid_update_cpu_capacity_scaling();
>  }
>
> -static void hybrid_init_cpu_capacity_scaling(bool refresh)
> +static void hybrid_refresh_cpu_capacity_scaling(void)
>  {
> -       bool disable_itmt = false;
> +       guard(mutex)(&hybrid_capacity_lock);
>
> -       mutex_lock(&hybrid_capacity_lock);
> +       __hybrid_refresh_cpu_capacity_scaling();
> +}
>
> +static void hybrid_init_cpu_capacity_scaling(bool refresh)
> +{
>         /*
>          * If hybrid_max_perf_cpu is set at this point, the hybrid CPU capacity
>          * scaling has been enabled already and the driver is just changing the
>          * operation mode.
>          */
>         if (refresh) {
> -               __hybrid_init_cpu_capacity_scaling();
> -               goto unlock;
> +               hybrid_refresh_cpu_capacity_scaling();
> +               return;
>         }
>
>         /*
> @@ -1056,19 +1059,13 @@ static void hybrid_init_cpu_capacity_sca
>          * do not do that when SMT is in use.
>          */
>         if (hwp_is_hybrid && !sched_smt_active() && arch_enable_hybrid_capacity_scale()) {
> -               __hybrid_init_cpu_capacity_scaling();
> -               disable_itmt = true;
> -       }
> -
> -unlock:
> -       mutex_unlock(&hybrid_capacity_lock);
> -
> -       /*
> -        * Disabling ITMT causes sched domains to be rebuilt to disable asym
> -        * packing and enable asym capacity.
> -        */
> -       if (disable_itmt)
> +               hybrid_refresh_cpu_capacity_scaling();
> +               /*
> +                * Disabling ITMT causes sched domains to be rebuilt to disable asym
> +                * packing and enable asym capacity.
> +                */
>                 sched_clear_itmt_support();
> +       }
>  }
>
>  static bool hybrid_clear_max_perf_cpu(void)
> @@ -1404,7 +1401,7 @@ static void intel_pstate_update_limits_f
>         mutex_lock(&hybrid_capacity_lock);
>
>         if (hybrid_max_perf_cpu)
> -               __hybrid_init_cpu_capacity_scaling();
> +               __hybrid_refresh_cpu_capacity_scaling();
>
>         mutex_unlock(&hybrid_capacity_lock);
>  }
>
>
>
>