linux-kernel - Re: [PATCH 0/6] Backport rework of deadline bandwidth restoration for 5.10.y

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Message-ID: <883a5a4f-b34e-689c-2fbd-7bf03db532eb@redhat.com>
Date:   Sun, 20 Aug 2023 12:24:33 -0400
From:   Waiman Long <longman@...hat.com>
To:     Qais Yousef <qyousef@...alina.io>, stable@...r.kernel.org
Cc:     Juri Lelli <juri.lelli@...hat.com>, Tejun Heo <tj@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...nel.org>, Hao Luo <haoluo@...gle.com>,
        John Stultz <jstultz@...gle.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] Backport rework of deadline bandwidth restoration for
 5.10.y


On 8/20/23 11:21, Qais Yousef wrote:
> This is a backport of the series that fixes the way deadline bandwidth
> restoration is done which is causing noticeable delay on resume path. It also
> converts the cpuset lock back into a mutex which some users on Android too.
> I lack the details but AFAIU the read/write semaphore was slower on high
> contention.

Note that it was a percpu rwsem before this patch series. It was not a 
regular rwsem. Percpu rwsem isn't designed to handle high write lock 
contention. A regular rwsem should be similar to mutex in performance 
when handling high write lock contention.

Cheers,
Longman