Re: [PATCH 1/4] sched/fair: Be less aggressive in calling cpufreq_update_util()

From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Qais Yousef <qyousef@layalina.io>, Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Vincent Guittot <vincent.guittot@linaro.org>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	Lukasz Luba <lukasz.luba@arm.com>, Wei Wang <wvw@google.com>,
	Rick Yiu <rickyiu@google.com>,
	Chung-Kai Mei <chungkai@google.com>,
	Hongyan Xia <hongyan.xia2@arm.com>
Subject: Re: [PATCH 1/4] sched/fair: Be less aggressive in calling cpufreq_update_util()
Date: Tue, 12 Dec 2023 11:46:35 +0100	[thread overview]
Message-ID: <47ef274b-d9cc-4f4f-8134-2dced46005fa@arm.com> (raw)
In-Reply-To: <20231208015242.385103-2-qyousef@layalina.io>

On 08/12/2023 02:52, Qais Yousef wrote:
> Due to the way code is structured, it makes a lot of sense to trigger
> cpufreq_update_util() from update_load_avg(). But this is too aggressive
> as in most cases we are iterating through entities in a loop to
> update_load_avg() in the hierarchy. So we end up sending too many
> request in an loop as we're updating the hierarchy.

But update_load_avg() calls cfs_rq_util_change() which only issues a
cpufreq_update_util() call for the root cfs_rq?

So the 'iterating through entities' should be for a task in a non-root
taskgroup which the condition (1) takes care of.

cfs_rq_util_change()

    ...
    if (&rq->cfs == cfs_rq) (1)

        cpufreq_update_util()

[...]