linux-kernel - Re: [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence of idle CPUs

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Message-ID: <20191210063303.pubbpu77ah2veuj7@vireshk-i7>
Date:   Tue, 10 Dec 2019 12:03:03 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Todd Kjos <tkjos@...gle.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        quentin.perret@...aro.org, chris.redpath@....com,
        steven.sistare@...cle.com, subhra.mazumdar@...cle.com,
        songliubraving@...com
Subject: Re: [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence
 of idle CPUs

On 09-12-19, 11:50, Wanpeng Li wrote:
> On Wed, 26 Jun 2019 at 13:07, Viresh Kumar <viresh.kumar@...aro.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

-- 
viresh

[1] https://pastebin.com/TMHGGBxD