linux-kernel - Re: [PATCH v2 3/3] x86, sched: Bail out of frequency invariance if turbo_freq/base

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Date:   Wed, 3 Jun 2020 16:51:21 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Giovanni Gherdovich <ggherdovich@...e.cz>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH v2 3/3] x86, sched: Bail out of frequency invariance if
 turbo_freq/base_freq gives 0

On Sun, May 31, 2020 at 8:26 PM Giovanni Gherdovich <ggherdovich@...e.cz> wrote:
>
> Be defensive against the case where the processor reports a base_freq
> larger than turbo_freq (the ratio would be zero).
>
> Signed-off-by: Giovanni Gherdovich <ggherdovich@...e.cz>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  arch/x86/kernel/smpboot.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index fe154c8226ba..f619007f46cf 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1976,6 +1976,7 @@ static bool core_set_max_freq_ratio(u64 *base_freq, u64 *turbo_freq)
>  static bool intel_set_max_freq_ratio(void)
>  {
>         u64 base_freq, turbo_freq;
> +       u64 turbo_ratio;
>
>         if (slv_set_max_freq_ratio(&base_freq, &turbo_freq))
>                 goto out;
> @@ -2009,9 +2010,15 @@ static bool intel_set_max_freq_ratio(void)
>                 return false;
>         }
>
> -       arch_turbo_freq_ratio = div_u64(turbo_freq * SCHED_CAPACITY_SCALE,
> -                                       base_freq);
> +       turbo_ratio = div_u64(turbo_freq * SCHED_CAPACITY_SCALE, base_freq);
> +       if (!turbo_ratio) {
> +               pr_debug("Non-zero turbo and base frequencies led to a 0 ratio.\n");
> +               return false;
> +       }
> +
> +       arch_turbo_freq_ratio = turbo_ratio;
>         arch_set_max_freq_ratio(turbo_disabled());
> +
>         return true;
>  }
>
> --
> 2.16.4
>