linux-kernel - Re: [PATCH v9 3/8] cpuset: Rebuild root domain deadline accounting information

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Date:   Sun, 15 Jan 2023 16:41:48 +0000
From:   Qais Yousef <qyousef@...alina.io>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Juri Lelli <juri.lelli@...hat.com>, peterz@...radead.org,
        mingo@...hat.com, rostedt@...dmis.org, tj@...nel.org,
        linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org, lizefan@...wei.com,
        longman@...hat.com, dietmar.eggemann@....com,
        cgroups@...r.kernel.org, Wei Wang <wvw@...gle.com>,
        Rick Yiu <rickyiu@...gle.com>,
        Quentin Perret <qperret@...gle.com>
Subject: Re: [PATCH v9 3/8] cpuset: Rebuild root domain deadline accounting
 information

On 12/20/22 11:43, Qais Yousef wrote:
> On 12/19/22 09:07, Vincent Guittot wrote:
> > On Sat, 17 Dec 2022 at 00:35, Qais Yousef <qyousef@...alina.io> wrote:
> > >
> > > Hi
> > >
> > > On 07/19/19 15:59, Juri Lelli wrote:
> > > > When the topology of root domains is modified by CPUset or CPUhotplug
> > > > operations information about the current deadline bandwidth held in the
> > > > root domain is lost.
> > > >
> > > > This patch addresses the issue by recalculating the lost deadline
> > > > bandwidth information by circling through the deadline tasks held in
> > > > CPUsets and adding their current load to the root domain they are
> > > > associated with.
> > > >
> > > > Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> > > > Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
> > > > ---
> > >
> > > We see that rebuild_root_domain() can take 10+ ms (I get a max of 20ms quite
> > > consistently) on suspend/resume.
> > >
> > > Do we actually need to rebuild_root_domain() if we're going through
> > > a suspend/resume cycle?
> > 
> > During suspend to ram, there are cpus hotplug operation but If you use
> > suspend to idle, you will skip cpus hotplug operation and its
> > associated rebuild.
> 
> Thanks Vincent. I'll check on that - but if we want to keep suspend to ram?
> Do we really to incur this hit?

Using s2idle is not an option actually. I'll prepare v2 to address Waiman
comment if I don't get more feedback in the next few days.


Thanks!

--
Qais Yousef