linux-kernel - Re: [PATCH 1/2] sched: cpufreq: ignore SMT when determining max cpu capacity

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Date:   Wed, 31 Aug 2016 03:27:30 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Steve Muckle <steve.muckle@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.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 1/2] sched: cpufreq: ignore SMT when determining max cpu capacity

On Friday, August 26, 2016 11:40:47 AM Steve Muckle wrote:
> PELT does not consider SMT when scaling its utilization values via
> arch_scale_cpu_capacity(). The value in rq->cpu_capacity_orig does
> take SMT into consideration though and therefore may be smaller than
> the utilization reported by PELT.
> 
> On an Intel i7-3630QM for example rq->cpu_capacity_orig is 589 but
> util_avg scales up to 1024. This means that a 50% utilized CPU will show
> up in schedutil as ~86% busy.
> 
> Fix this by using the same CPU scaling value in schedutil as that which
> is used by PELT.
> 
> Signed-off-by: Steve Muckle <smuckle@...aro.org>

This is fine by me.

Peter, any objections?

> ---
>  kernel/sched/cpufreq_schedutil.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 60d985f4dc47..cb8a77b1ef1b 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -147,7 +147,9 @@ static unsigned int get_next_freq(struct sugov_cpu *sg_cpu, unsigned long util,
>  static void sugov_get_util(unsigned long *util, unsigned long *max)
>  {
>  	struct rq *rq = this_rq();
> -	unsigned long cfs_max = rq->cpu_capacity_orig;
> +	unsigned long cfs_max;
> +
> +	cfs_max = arch_scale_cpu_capacity(NULL, smp_processor_id());
>  
>  	*util = min(rq->cfs.avg.util_avg, cfs_max);
>  	*max = cfs_max;
> 

Thanks,
Rafael