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

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Message-ID: <20160824083138.GA3315@e105550-lin.cambridge.arm.com>
Date:   Wed, 24 Aug 2016 09:31:39 +0100
From:   Morten Rasmussen <morten.rasmussen@....com>
To:     Steve Muckle <steve.muckle@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        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>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Juri Lelli <Juri.Lelli@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Steve Muckle <smuckle@...aro.org>
Subject: Re: [PATCH] sched: cpufreq: ignore SMT when determining max cpu
 capacity

On Fri, Aug 19, 2016 at 01:43:47PM -0700, 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>
> ---
>  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());

Until we have figured out how to define utilization (and capacity)
better for SMT I think this is a better solution.

Morten