Re: [patch 01/10] x86/aperfmperf: Dont wake idle CPUs in arch_freq_get_on_cpu()

[Rafael J. Wysocki]

On Fri, Apr 15, 2022 at 9:19 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> aperfmperf_get_khz() already excludes idle CPUs from APERF/MPERF sampling
> and that's a reasonable decision. There is no point in sending up to two
> IPIs to an idle CPU just because someone reads a sysfs file.
>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

> ---
>  arch/x86/kernel/cpu/aperfmperf.c |    3 +++
>  1 file changed, 3 insertions(+)
>
> --- a/arch/x86/kernel/cpu/aperfmperf.c
> +++ b/arch/x86/kernel/cpu/aperfmperf.c
> @@ -139,6 +139,9 @@ unsigned int arch_freq_get_on_cpu(int cp
>         if (!housekeeping_cpu(cpu, HK_TYPE_MISC))
>                 return 0;
>
> +       if (rcu_is_idle_cpu(cpu))
> +               return 0;
> +
>         if (aperfmperf_snapshot_cpu(cpu, ktime_get(), true))
>                 return per_cpu(samples.khz, cpu);
>
>