Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 3 Nov 2022 14:27:32 +0000
From:   Qais Yousef <qyousef@layalina.io>
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
        linux-kernel@vger.kernel.org, parth@linux.ibm.com,
        qais.yousef@arm.com, chris.hyser@oracle.com,
        patrick.bellasi@matbug.net, David.Laight@aculab.com,
        pjt@google.com, pavel@ucw.cz, tj@kernel.org, qperret@google.com,
        tim.c.chen@linux.intel.com, joshdon@google.com, timj@gnu.org,
        kprateek.nayak@amd.com, yu.c.chen@intel.com,
        youssefesmat@chromium.org, joel@joelfernandes.org
Subject: Re: [PATCH v7 6/9] sched/fair: Add sched group latency support
Message-ID: <20221103142732.m5ibwkuymvhcdxkn@airbuntu>
References: <20221028093403.6673-1-vincent.guittot@linaro.org>
 <20221028093403.6673-7-vincent.guittot@linaro.org>
 <20221101192848.pjns3um7dnrwrk5p@airbuntu>
 <CAKfTPtA=vJQA_=6Un1CqwzMUaOxMeFGTKUZnj8qyqvqmSdYBAg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAKfTPtA=vJQA_=6Un1CqwzMUaOxMeFGTKUZnj8qyqvqmSdYBAg@mail.gmail.com>
Precedence: bulk

On 11/03/22 09:46, Vincent Guittot wrote:
> On Tue, 1 Nov 2022 at 20:28, Qais Yousef <qyousef@layalina.io> wrote:
> >
> > On 10/28/22 11:34, Vincent Guittot wrote:
> > > Task can set its latency priority with sched_setattr(), which is then used
> > > to set the latency offset of its sched_enity, but sched group entities
> > > still have the default latency offset value.
> > >
> > > Add a latency.nice field in cpu cgroup controller to set the latency
> > > priority of the group similarly to sched_setattr(). The latency priority
> > > is then used to set the offset of the sched_entities of the group.
> > >
> > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> > > ---
> > >  Documentation/admin-guide/cgroup-v2.rst |  8 ++++
> > >  kernel/sched/core.c                     | 52 +++++++++++++++++++++++++
> > >  kernel/sched/fair.c                     | 33 ++++++++++++++++
> > >  kernel/sched/sched.h                    |  4 ++
> > >  4 files changed, 97 insertions(+)
> > >
> > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> > > index be4a77baf784..d8ae7e411f9c 100644
> > > --- a/Documentation/admin-guide/cgroup-v2.rst
> > > +++ b/Documentation/admin-guide/cgroup-v2.rst
> > > @@ -1095,6 +1095,14 @@ All time durations are in microseconds.
> > >          values similar to the sched_setattr(2). This maximum utilization
> > >          value is used to clamp the task specific maximum utilization clamp.
> > >
> > > +  cpu.latency.nice
> > > +     A read-write single value file which exists on non-root
> > > +     cgroups.  The default is "0".
> > > +
> > > +     The nice value is in the range [-20, 19].
> > > +
> > > +     This interface file allows reading and setting latency using the
> > > +     same values used by sched_setattr(2).
> >
> > I'm still not sure about this [1].
> 
> I'm still not sure about what you are trying to say here ...
> 
> This is about setting a latency nice prio to a group level.
> 
> >
> > In some scenarios we'd like to get the effective latency_nice of the task. How
> > will the task inherit the cgroup value or be impacted by it?
> >
> > For example if there are tasks that belong to a latency sensitive cgroup; and
> > I'd like to skip some searches in EAS to improve that latency sensitivity - how
> > would I extract this info in EAS path given these tasks are using default
> > latency_nice value? And if should happen if their latency_nice is set to
> > something else other than default?
> >
> > [1] https://lore.kernel.org/lkml/20221012160734.hrkb5jcjdq7r23pr@wubuntu/
> 
> Hmm so you are speaking about something that is not part of the patch.
> Let focus on the patchset for now

I am focusing on this patchset. Isn't this an essential part of the design?
Once the interface is out we can't change it. As it stands, I can't see how it
can be used to replace prefer_idle in cgroup as used in Android. I can't see
how this could happen if we don't define how the task will inherit the cgroup
value. If we can, mind elaborating how please?


Thanks

--
Qais Yousef