Re: [PATCH v2 2/3] x86, sched: Bail out of frequency invariance if turbo frequency is unknown

[Rafael J. Wysocki]

On Sun, May 31, 2020 at 8:26 PM Giovanni Gherdovich <ggherdovich@xxxxxxx> wrote:
>
> There may be CPUs that support turbo boost but don't declare any turbo
> ratio, i.e. their MSR_TURBO_RATIO_LIMIT is all zeroes. In that condition
> scale-invariant calculations can't be performed.
>
> Signed-off-by: Giovanni Gherdovich <ggherdovich@xxxxxxx>
> Suggested-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")

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

> ---
>  arch/x86/kernel/smpboot.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index d660966d7de7..fe154c8226ba 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -2001,9 +2001,11 @@ static bool intel_set_max_freq_ratio(void)
>         /*
>          * Some hypervisors advertise X86_FEATURE_APERFMPERF
>          * but then fill all MSR's with zeroes.
> +        * Some CPUs have turbo boost but don't declare any turbo ratio
> +        * in MSR_TURBO_RATIO_LIMIT.
>          */
> -       if (!base_freq) {
> -               pr_debug("Couldn't determine cpu base frequency, necessary for scale-invariant accounting.\n");
> +       if (!base_freq || !turbo_freq) {
> +               pr_debug("Couldn't determine cpu base or turbo frequency, necessary for scale-invariant accounting.\n");
>                 return false;
>         }
>
> --
> 2.16.4
>