linux-kernel - Re: [patch] CFS scheduler, -v5

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Date:	Mon, 23 Apr 2007 05:08:00 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Gene Heskett <gene.heskett@...il.com>
Cc:	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Mike Galbraith <efault@....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>, Mark Lord <lkml@....ca>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [patch] CFS scheduler, -v5

* Gene Heskett <gene.heskett@...il.com> wrote:

> I haven't approached that yet, but I just noticed, having been booted 
> to this for all of 5 minutes, that although I told it not to renice x 
> when my script ran 'make oldconfig', and I answered n, but there it 
> is, sitting at -19 according to htop.
> 
> The .config says otherwise:
> [root@...ote linux-2.6.21-rc7-CFS-v5]# grep RENICE .config
> # CONFIG_RENICE_X is not set
> 
> So v5 reniced X in spite of the 'no' setting.

Hmm, apparently your X uses ioperm() while mine uses iopl(), and i only 
turned off the renicing for iopl. (I fixed this in my tree and it will 
show up in -v6.)

> Although I hadn't noticed it, one way or the other, I just set it (X) 
> back to the default -1 so that I'm comparing the same apples when I do 
> compare.

note that CFS handles negative nice levels differently from other 
schedulers, so the disadvantages of agressively reniced X (lost 
throughput due to overscheduling, worse interactivity) do _not_ apply to 
CFS.

I think the 'fair' setting would be whatever the scheduler writer 
recommends: for SD, X probably performs better at around nice 0 (i'll 
let Con correct me if his experience is different). On CFS, nice -10 is 
perfectly fine too, and you'll have a zippier desktop under higher 
loads. (on servers this might be unnecessary/disadvantegous so there 
this can be turned off.)

(also, in my tree i've changed the default from -19 to -10 to make it 
less scary to people and to leave more levels to the sysadmin, this 
change too will show up in -v6.)

	Ingo
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