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

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Date:   Mon, 21 Aug 2023 00:02:57 +0100
From:   Qais Yousef <qyousef@...alina.io>
To:     Waiman Long <longman@...hat.com>
Cc:     stable@...r.kernel.org, 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 08/20/23 12:24, Waiman Long wrote:
> 
> 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.

Thanks a lot for the clarification Waiman! Much appreciated.


Cheers

--
Qais Yousef