linux-kernel - Re: niced tasks on SMT system

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Message-ID: <20171228205933.GB20142@amd>
Date:   Thu, 28 Dec 2017 21:59:33 +0100
From:   Pavel Machek <pavel@....cz>
To:     Ozgur <ozgur@...sey.org>
Cc:     Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        kernel list <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>
Subject: Re: niced tasks on SMT system

Hi!

> >>  > Ok, so I'm compiling, and I'd like to run a flight simulator.
> >>  >
> >>  > Flightgear normally does 20fps on my system... kinda low but playable.
> >>  >
> >>  > I have reniced make -j 5 fo kernel running. Scheduler gives 100% of
> >>  > one of CPUs to Flightgear (good), but the smt sibling is used by the
> >>  > compilation, and I'm down to 9 fps. Not good.
> >>  >
> >>  > Even with single-threaded make, I have 10-13fps.
> >>  >
> >>  > Is there way to learn which CPUs are SMT siblings?
> >>
> >>  cat /sys/devices/system/cpu/cpu{N}/topology/thread_siblings
> >
> > Thanks for a hint.
> >
> > Well, something is definitely wrong there:
> >
> > pavel@duo:/data/l/linux-n900$ cat
> > /sys/devices/system/cpu/cpu0/topology/thread_siblings
> > 03
> 
> Ops,
> 
> do you fly on N900 via flightgear? :)
> I have two N900 and one run gentoo.

No, no flightgear on N900. It was preparing kernels for my N900 that
interfered with flying.

BTW there's  lot of fun to be had with
N900. https://wiki.postmarketos.org/wiki/Nokia_N900_(nokia-rx51) I
even have voice calls working on Debian, help welcome :-).
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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