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Date: Tue, 17 Apr 2007 10:20:36 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Davide Libenzi <davidel@xmailserver.org>
Cc: Gene Heskett <gene.heskett@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Con Kolivas <kernel@kolivas.org>, Nick Piggin <npiggin@suse.de>,
       Mike Galbraith <efault@gmx.de>, Arjan van de Ven <arjan@infradead.org>,
       Peter Williams <pwil3058@bigpond.net.au>,
       Thomas Gleixner <tglx@linutronix.de>, caglar@pardus.org.tr,
       Willy Tarreau <w@1wt.eu>, Dmitry Adamushko <dmitry.adamushko@gmail.com>
Subject: Re: [patch] CFS (Completely Fair Scheduler), v2
Message-ID: <20070417082036.GC5076@elte.hu>
References: <20070416220715.GA4071@elte.hu> <200704170053.58611.gene.heskett@gmail.com> <20070417061849.GA12385@elte.hu> <Pine.LNX.4.64.0704170053410.30516@alien.or.mcafeemobile.com>
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* Davide Libenzi <davidel@xmailserver.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