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From: Vikram Mulukutla <markivx@codeaurora.org>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Juri Lelli <juri.lelli@arm.com>,
	Joel Fernandes <joelaf@google.com>,
	Andres Oportus <andresoportus@google.com>,
	Todd Kjos <tkjos@android.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	linux-kernel-owner@vger.kernel.org
Subject: Re: [PATCH v2 4/6] cpufreq: schedutil: update CFS util only if used
Date: Thu, 06 Jul 2017 23:44:09 -0700	[thread overview]
Message-ID: <c04bdad3354a0ee0aabe63fe813fdaf5@codeaurora.org> (raw)
In-Reply-To: <1499189651-18797-5-git-send-email-patrick.bellasi@arm.com>

On 2017-07-04 10:34, Patrick Bellasi wrote:
> Currently the utilization of the FAIR class is collected before locking
> the policy. Although that should not be a big issue for most cases, we
> also don't really know how much latency there can be between the
> utilization reading and its usage.
> 
> Let's get the FAIR utilization right before its usage to be better in
> sync with the current status of a CPU.
> 
> Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> ---
>  kernel/sched/cpufreq_schedutil.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c 
> b/kernel/sched/cpufreq_schedutil.c
> index 98704d8..df433f1 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -308,10 +308,9 @@ static void sugov_update_shared(struct
> update_util_data *hook, u64 time,
>  	if (unlikely(current == sg_policy->thread))
>  		return;
> 
> -	sugov_get_util(&util, &max);
> -
>  	raw_spin_lock(&sg_policy->update_lock);
> 
> +	sugov_get_util(&util, &max);
>  	sg_cpu->util = util;
>  	sg_cpu->max = max;

Given that the utilization update hooks are called with the per-cpu rq 
lock held (for all classes), I don't think PELT utilization can change 
throughout the lifetime of the cpufreq_update_{util,this_cpu} call? Even 
with Viresh's remote cpu callback series we'd still have to hold the rq 
lock across cpufreq_update_util..  what can change today is 'max' 
(arch_scale_cpu_capacity) when a cpufreq policy is shared, so the patch 
is still needed for that reason I think?

Thanks,
Vikram

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

  parent reply	other threads:[~2017-07-07  6:44 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-04 17:34 [PATCH v2 0/6] cpufreq: schedutil: fixes for flags updates Patrick Bellasi
2017-07-04 17:34 ` [PATCH v2 1/6] cpufreq: schedutil: ignore sugov kthreads Patrick Bellasi
2017-07-05  5:00   ` Viresh Kumar
2017-07-05 11:38     ` Patrick Bellasi
2017-07-06  4:50       ` Viresh Kumar
2017-07-06 22:18       ` Rafael J. Wysocki
2017-07-11 19:08   ` Saravana Kannan
2017-07-04 17:34 ` [PATCH v2 2/6] cpufreq: schedutil: reset sg_cpus's flags at IDLE enter Patrick Bellasi
2017-07-05  4:50   ` Viresh Kumar
2017-07-05 13:04     ` Patrick Bellasi
2017-07-06  5:46       ` Viresh Kumar
2017-07-07  4:43   ` Joel Fernandes
2017-07-07 10:17     ` Juri Lelli
2017-07-11 19:16       ` Saravana Kannan
2017-07-04 17:34 ` [PATCH v2 3/6] cpufreq: schedutil: ensure max frequency while running RT/DL tasks Patrick Bellasi
2017-07-05  6:01   ` Viresh Kumar
2017-07-05 13:41     ` Patrick Bellasi
2017-07-06  5:56       ` Viresh Kumar
2017-07-07  5:26       ` Joel Fernandes
2017-07-04 17:34 ` [PATCH v2 4/6] cpufreq: schedutil: update CFS util only if used Patrick Bellasi
2017-07-07  5:58   ` Joel Fernandes
2017-07-07  6:44   ` Vikram Mulukutla [this message]
2017-07-08  6:14     ` Joel Fernandes
2017-07-10 17:49       ` Vikram Mulukutla
2017-07-11  5:19         ` Joel Fernandes
2017-07-04 17:34 ` [PATCH v2 5/6] sched/rt: fast switch to maximum frequency when RT tasks are scheduled Patrick Bellasi
2017-07-04 17:34 ` [PATCH v2 6/6] cpufreq: schedutil: relax rate-limiting while running RT/DL tasks Patrick Bellasi
2017-07-06 22:26 ` [PATCH v2 0/6] cpufreq: schedutil: fixes for flags updates Rafael J. Wysocki

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