linux-kernel - Re: [PATCH] sched: fix incorrect PELT values on SMT

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Date:   Fri, 19 Aug 2016 10:30:36 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Steve Muckle <steve.muckle@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Juri Lelli <Juri.Lelli@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Steve Muckle <smuckle@...aro.org>
Subject: Re: [PATCH] sched: fix incorrect PELT values on SMT

2016-08-19 9:55 GMT+08:00 Steve Muckle <steve.muckle@...aro.org>:
> PELT scales its util_sum and util_avg values via
> arch_scale_cpu_capacity(). If that function is passed the CPU's sched
> domain then it will reduce the scaling capacity if SD_SHARE_CPUCAPACITY
> is set. PELT does not pass in the sd however. The other caller of
> arch_scale_cpu_capacity, update_cpu_capacity(), does. This means
> util_sum and util_avg scale beyond the CPU capacity on SMT.
>
> On an Intel i7-3630QM for example rq->cpu_capacity_orig is 589 but
> util_avg scales up to 1024.
>
> Fix this by passing in the sd in __update_load_avg() as well.

I believe we notice this at least several months ago.
https://lkml.org/lkml/2016/5/25/228

>
> Signed-off-by: Steve Muckle <smuckle@...aro.org>
> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 61d485421bed..95d34b337152 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2731,7 +2731,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
>         sa->last_update_time = now;
>
>         scale_freq = arch_scale_freq_capacity(NULL, cpu);
> -       scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
> +       scale_cpu = arch_scale_cpu_capacity(cpu_rq(cpu)->sd, cpu);
>
>         /* delta_w is the amount already accumulated against our next period */
>         delta_w = sa->period_contrib;
> --
> 2.7.3
>



-- 
Regards,
Wanpeng Li