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From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Tue, 10 Dec 2019 19:15:34 +0800
Message-ID: <CANRm+Czph-WDBm+L8+ykq4FZahsX3fWFV=n8_NwQJQwHoUHoWg@mail.gmail.com>
Subject: Re: [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence
 of idle CPUs
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Todd Kjos <tkjos@google.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        quentin.perret@linaro.org, chris.redpath@arm.com,
        steven.sistare@oracle.com, subhra.mazumdar@oracle.com,
        songliubraving@fb.com
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On Tue, 10 Dec 2019 at 14:33, Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> On 09-12-19, 11:50, Wanpeng Li wrote:
> > On Wed, 26 Jun 2019 at 13:07, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> > >
> > > Hi,
> > >
> > > We try to find an idle CPU to run the next task, but in case we don't
> > > find an idle CPU it is better to pick a CPU which will run the task the
> > > soonest, for performance reason.
> > >
> > > A CPU which isn't idle but has only SCHED_IDLE activity queued on it
> > > should be a good target based on this criteria as any normal fair task
> > > will most likely preempt the currently running SCHED_IDLE task
> > > immediately. In fact, choosing a SCHED_IDLE CPU over a fully idle one
> > > shall give better results as it should be able to run the task sooner
> > > than an idle CPU (which requires to be woken up from an idle state).
> > >
> > > This patchset updates both fast and slow paths with this optimization.
> > >
> > > Testing is done with the help of rt-app currently and here are the
> > > details:
> > >
> > > - Tested on Octacore Hikey platform (all CPUs change frequency
> > >   together).
> > >
> > > - rt-app json [1] creates few tasks and we monitor the scheduling
> > >   latency for them by looking at "wu_lat" field (usec).
> > >
> > > - The histograms are created using
> > >   https://github.com/adkein/textogram: textogram -a 0 -z 1000 -n 10
> > >
> > > - the stats are accumulated using: https://github.com/nferraz/st
> >
> > Hi Viresh,
> >
> > Thanks for the great work! Could you give the whole commad-line for us testing?
>
> The rt-app json [1] can be run using:
>
> $ rt-app sched-idle.json
>
> This will create couple of files named rt-app-cfs_thread-*.log and
> rt-app-idle_thread-*.log. I looked mostly at the cfs files here as that's what
> we were looking for. We will be interested only in the last column of these
> files, which says "wu_lat". Remove everything apart from that column (and remove
> the first row as well, which has field names) from all cfs files (or write a
> sed/awk command to do it for you.
>
> After that I you can generate the numbers (mean/max/min/etc) using:
>
> $ st rt-app-cfs_thread-*.log

Thanks for pointing out this.

    Wanpeng