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Date: Tue, 12 Dec 2023 18:22:23 +0000
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Subject: Re: [PATCH 1/4] sched/fair: Be less aggressive in calling
 cpufreq_update_util()
To: Qais Yousef <qyousef@layalina.io>,
 Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: 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>, 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>
References: <20231208015242.385103-1-qyousef@layalina.io>
 <20231208015242.385103-2-qyousef@layalina.io>
 <47ef274b-d9cc-4f4f-8134-2dced46005fa@arm.com>
 <20231212123535.3yns5f4b6awiuesk@airbuntu>
Content-Language: en-US
From: Hongyan Xia <hongyan.xia2@arm.com>
In-Reply-To: <20231212123535.3yns5f4b6awiuesk@airbuntu>
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On 12/12/2023 12:35, Qais Yousef wrote:
> On 12/12/23 11:46, Dietmar Eggemann wrote:
>> 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?
> 
> Yes I've noticed that and wondered. Maybe my analysis was flawed and I was just
> hitting the issue of iowait boost request conflicting with update_load_avg()
> request.
> 
> Let me have another look. I think we'll still end up needing to take the update
> out of util_avg to be able to combine the two calls.

I agree. Currently it does not express the intention clearly. We only 
want to update the root CFS but the code was written in a misleading way 
that suggests we want to update for every cfs_rq. A single update at the 
end looks much nicer and makes other patches easier.

Hongyan