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Date: Tue, 24 Apr 2007 10:23:06 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Michael Gerdau <mgd@technosis.de>
Cc: linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Nick Piggin <npiggin@suse.de>, Gene Heskett <gene.heskett@gmail.com>,
       Juliusz Chroboczek <jch@pps.jussieu.fr>, Mike Galbraith <efault@gmx.de>,
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       Andrew Morton <akpm@linux-foundation.org>,
       Bill Davidsen <davidsen@tmr.com>, Willy Tarreau <w@1wt.eu>,
       Arjan van de Ven <arjan@infradead.org>
Subject: Re: [REPORT] cfs-v5 vs sd-0.46
Message-ID: <20070424082305.GA6332@elte.hu>
References: <200704240938.07482.mgd@technosis.de> <20070424075319.GA30909@elte.hu> <200704241017.10610.mgd@technosis.de>
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* Michael Gerdau <mgd@technosis.de> wrote:

> > so to be totally 'fair' and get the same rescheduling 'granularity' 
> > you should probably lower CFS's sched_granularity_ns to 2 msecs.
> 
> I'll change default nice in cfs to -10.
> 
> I'm also happy to adjust /proc/sys/kernel/sched_granularity_ns to 
> 2msec. However checking /proc/sys/kernel/rr_interval reveals it is 16 
> (msec) on my system.

ah, yeah - there due to the SMP rule in SD:

       rr_interval *= 1 + ilog2(num_online_cpus());

and you have a 2-CPU system, so you get 8msec*2 == 16 msecs default 
interval. I find this a neat solution and i have talked to Con about 
this already and i'll adopt Con's idea in CFS too. Nevertheless, despite 
the settings, SD seems to be rescheduling every 6-7 msecs, while CFS 
reschedules only every 13 msecs.

Here i'm assuming that the vmstats are directly comparable: that your 
number-crunchers behave the same during the full runtime - is that 
correct? (If not then the vmstat result should be run at roughly the 
same type of "stage" of the workload, on all the schedulers.)

	Ingo