linux-kernel - Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

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Message-ID: <20070414105338.GB19454@elte.hu>
Date:	Sat, 14 Apr 2007 12:53:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Willy Tarreau <w@....eu>
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>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

* Willy Tarreau <w@....eu> wrote:

> Forking becomes very slow above a load of 100 it seems. Sometimes, the 
> shell takes 2 or 3 seconds to return to prompt after I run "scheddos 
> &"

this might be changed/impacted by the parent-requeue fix that is in the 
updated (for real, promise! ;) patch. Right now on CFS a forking parent 
shares its own run stats with the child 50%/50%. This means that heavy 
forkers are indeed penalized. Another logical choice would be 100%/0%: a 
child has to earn its own right.

i kept the 50%/50% rule from the old scheduler, but maybe it's a more 
pristine (and smaller/faster) approach to just not give new children any 
stats history to begin with. I've implemented an add-on patch that 
implements this, you can find it at:

    http://redhat.com/~mingo/cfs-scheduler/sched-fair-fork.patch

> Those are very promising results, I nearly observe the same 
> responsiveness as I had on a solaris 10 with 10k running processes on 
> a bigger machine.

cool and thanks for the feedback! (Btw., as another test you could also 
try to renice "scheddos" to +19. While that does not push the scheduler 
nearly as hard as nice 0, it is perhaps more indicative of how a truly 
abusive many-tasks workload would be run in practice.)

	Ingo
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