linux-kernel - Re: [patch] CFS scheduler, -v8

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Date:	Wed, 2 May 2007 12:40:38 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Galbraith <efault@....de>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Willy Tarreau <w@....eu>,
	Gene Heskett <gene.heskett@...il.com>, Mark Lord <lkml@....ca>,
	Zach Carter <linux@...hcarter.com>,
	buddabrod <buddabrod@...il.com>, Balbir Singh <balbir@...ibm.com>
Subject: Re: [patch] CFS scheduler, -v8

* Mike Galbraith <efault@....de> wrote:

> On Tue, 2007-05-01 at 23:22 +0200, Ingo Molnar wrote:
> >  - interactivity: precise load calculation and load smoothing
> 
> This seems to help quite a bit.

great :)

> (5 second top sample)
> 
>  2636 root      15  -5 19148  15m 5324 R   73  1.5   1:42.29 0 amarok_libvisua
>  5440 root      20   0  320m  36m 8388 S   18  3.6   3:28.55 1 Xorg
>  4621 root      20   0 22776  18m 4168 R   12  1.8   0:00.63 1 cc1
>  4616 root      20   0 19456  13m 2200 R    9  1.3   0:00.43 0 cc1
> 
> I no longer have to renice both X and Gforce to achieve a perfect 
> display when they are sharing my box with a make -j2.  X is displaying 
> everything it's being fed beautifully with no help.  I have to renice 
> Gforce (amarok_libvisual), but given it's very heavy CPU usage, that 
> seems perfectly fine.

ah! Besides OpenGL behavior and app startup performance i didnt 
originally have Xorg in mind with this change, but thinking about it, 
precise load calculations and load smoothing does have a positive effect 
on 'coupled' workloads where under the previous variant of CFS's load 
calculation one task component of the workload could become 'invisible' 
to another task and hence cause macro-scale scheduling artifacts not 
expected by humans. With smoothing these are dealt with more 
consistently. Xorg can be a quite strongly coupled workload.

> No regressions noticed so far.  Box is _very_ responsive under load, 
> seemingly even more so than with previous releases.  That is purely 
> subjective, but the first impression was very distinct.

yeah, make -jN workloads (and any mixture of non-identical scheduling 
patterns, which most real workloads consist of) should be handled more 
consistently too by -v8.

so your workload (and Gene's workload) were the ones in fact that i had 
hoped not to _hurt_ with -v8 (neither of you being the hardcore gamer 
type ;), and in reality -v8 ended up helping them too. These sorts of 
side-effects are always welcome ;-)

	Ingo
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