From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752533AbbJJRNz (ORCPT <rfc822;w@1wt.eu>);
	Sat, 10 Oct 2015 13:13:55 -0400
Received: from bombadil.infradead.org ([198.137.202.9]:55173 "EHLO
	bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752425AbbJJRNy (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sat, 10 Oct 2015 13:13:54 -0400
Date: Sat, 10 Oct 2015 19:13:51 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: paul.szabo@sydney.edu.au, linux-kernel@vger.kernel.org
Subject: Re: [patch] sched: disable task group re-weighting on the desktop
Message-ID: <20151010171351.GN11639@twins.programming.kicks-ass.net>
References: <1444292390.3389.100.camel@gmail.com>
 <201510081054.t98AsL1U003456@como.maths.usyd.edu.au>
 <20151008111959.GM3816@twins.programming.kicks-ass.net>
 <1444483369.2804.9.camel@gmail.com>
 <20151010170142.GI3816@twins.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20151010170142.GI3816@twins.programming.kicks-ass.net>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sat, Oct 10, 2015 at 07:01:42PM +0200, Peter Zijlstra wrote:
> On Sat, Oct 10, 2015 at 03:22:49PM +0200, Mike Galbraith wrote:
> > Ah, but now onward to interactivity...
> >
> > master, 8 groups of 1 (pert) vs desktop (mplayer BigBuckBunny-DivXPlusHD.mkv)
> >   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ P COMMAND
> >  4068 root      20   0    8312    724    628 R 99.64 0.004   1:04.32 6 pert
> >  4065 root      20   0    8312    744    648 R 99.45 0.005   1:04.92 5 pert
> >  4071 root      20   0    8312    748    652 R 99.27 0.005   1:03.12 7 pert
> >  4077 root      20   0    8312    840    744 R 98.72 0.005   1:01.46 3 pert
> >  4074 root      20   0    8312    796    700 R 98.18 0.005   1:03.38 1 pert
> >  4079 root      20   0    8312    720    624 R 97.99 0.004   1:01.45 4 pert
> >  4062 root      20   0    8312    836    740 R 96.72 0.005   1:03.44 0 pert
> >  4059 root      20   0    8312    720    624 R 94.16 0.004   1:04.92 2 pert
> >  4082 root      20   0 1094400 154324  33592 S 4.197 0.954   0:02.69 0 mplayer
> >  1029 root      20   0  465332 151540  40816 R 3.285 0.937   0:24.59 2 Xorg
> >  1773 root      20   0  662592  73308  42012 S 2.007 0.453   0:12.84 5 konsole
> >   771 root      20   0   11416   1964   1824 S 0.730 0.012   0:10.45 0 rngd
> >  1722 root      20   0 2866772  65224  51152 S 0.365 0.403   0:03.44 2 kwin
> >  1769 root      20   0  711684  54212  38020 S 0.182 0.335   0:00.39 1 kmix

Ah wait, so you have 8 groups of cycle soakers vs 1 group of desktop?
That means your desktop will get 1/9 th of the total time and that is
almost so:

 2.69+24.59+12.84+10.45+3.44+.39 = 54.4

vs

 (64.32+64.92+63.12+61.46+63.38+61.45+63.44+64.92)/8 = 63.37625

Which isn't too far off.

This really appears to be a case where you get what you ask for.