linux-kernel - Re: [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice

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Date:   Mon, 20 Apr 2020 15:14:31 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Parth Shah <parth@...ux.ibm.com>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Qais Yousef <qais.yousef@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Subhra Mazumdar <subhra.mazumdar@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Glexiner <tglx@...utronix.de>,
        steven.sistare@...cle.com, Dhaval Giani <dhaval.giani@...cle.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice

On Mon, Apr 20, 2020 at 04:56:55PM +0530, Parth Shah wrote:

> >>
> >> There are two presentations/discussions planned:
> >>
> >> "Introducing Latency Nice for Scheduler Hints and Optimizing Scheduler
> >> Task Wakeup" and "The latency nice use case for Energy-Aware-Scheduling
> >> (EAS) in Android Common Kernel (ACK)"
> >>
> >> We'll probably merge those two into one presentation/discussion.
> >>
> >> So far we have Parth's per-task implementation
> >>
> >> https://lore.kernel.org/lkml/20200228090755.22829-1-parth@linux.ibm.com
> > 
> > Cool, I see it has some Reviewed-by tags so that's a good sign. Will
> > look more into that.
> > 
> >> What's missing is the per-taskgroup implementation, at least from the
> >> standpoint of ACK.
> >>
> >> The (mainline) EAS use-case for latency nice is already in ACK
> >> (android-5.4):
> >>
> >> https://android.googlesource.com/kernel/common/+/760b82c9b88d2c8125abfc5f732cc3cd460b2a54
> > 
> > Yes, I was aware of this. But if we use task groups, then the
> > transition from schedtune -> uclamp means now the tasks that use
> > uclamp would also be subjected to cpu.shares. That's why we were
> > looking into the per-task interface and glad there's some work on this
> > already done.
> > 
> 
> Yes, that series of latency_nice seems to be in good shape to be used for
> any usecases. Hopefully, OSPM will lead to its upstreaming sooner :-)

Cool :)

> But at the end, we aim to have both the per-task and cgroup based interface
> to mark the latency_nice value of a task.

Ok. We'd likely use the per-task interface unless we decide to assign
cpu.shares for the groups as well.

> Till, then I'm finding some generic use-cases to show benefits of such task
> attribute to increase community interest.

Ok. Feel free to add ChromeOS as a usecase as well.

thanks,

 - Joel