linux-kernel - Re: [patch] CFS (Completely Fair Scheduler), v2

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Message-ID: <20070417082036.GC5076@elte.hu>
Date:	Tue, 17 Apr 2007 10:20:36 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Gene Heskett <gene.heskett@...il.com>,
	Linux Kernel Mailing List <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>, 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>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [patch] CFS (Completely Fair Scheduler), v2


* Davide Libenzi <davidel@...ilserver.org> wrote:

> > ok - fortunately the delta between -v2-rc0 and -v2-final is pretty 
> > small. One difference is the child-runs-first fix. To restore the 
> > parent-runs-first logic, do this:
> > 
> > 	echo 0 > /proc/sys/kernel/sched_child_runs_first
> 
> Sorry, I did not follow the latest developments, but how many tunables 
> we have so far in CFS? Are those for debug only or they're supposed to 
> stay?

yeah, debug only. I strongly suspect the Kaffeine breakage for example 
was related to child-runs-first, so userspace developers might be 
interested in a switch to turn this on/off.

while reviewing the upstream scheduler it occured to me that we are 
probably _not_ doing child-runs-first there due to the list_add_tail() 
[it should be a list_add() for it to be child-first. But i havent 
instrumented this heavily and this portion of the mainline scheduler is 
pretty fragile.]. So via this flag we could also see the performance 
impact, besides the compatibility impact.

> Weren't those listed inside the Axis of Evil (just to remain in topic
> :) till yesterday?

heh ;)

	Ingo
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