linux-kernel - Re: [ck] Re: [REPORT] cfs-v6-rc2 vs sd-0.46 vs 2.6.21-rc7

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Date:	Fri, 27 Apr 2007 08:59:36 +1000
From:	Con Kolivas <kernel@...ivas.org>
To:	ck@....kolivas.org
Cc:	Ingo Molnar <mingo@...e.hu>, Michael Gerdau <mgd@...hnosis.de>,
	Nick Piggin <npiggin@...e.de>,
	Bill Davidsen <davidsen@....com>,
	Juliusz Chroboczek <jch@....jussieu.fr>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
	William Lee Irwin III <wli@...omorphy.com>,
	Peter Williams <pwil3058@...pond.net.au>,
	Gene Heskett <gene.heskett@...il.com>,
	Willy Tarreau <w@....eu>, Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [ck] Re: [REPORT] cfs-v6-rc2 vs sd-0.46 vs 2.6.21-rc7

On Thursday 26 April 2007 22:07, Ingo Molnar wrote:
> * Michael Gerdau <mgd@...hnosis.de> wrote:
> > Hi list,
> >
> > find below a test comparing
> >     2.6.21-rc7 (mainline)
> >     2.6.21-rc7-sd046
> >     2.6.21-rc7-cfs-v6-rc2(*) (X @ nice 0)
> >     2.6.21-rc7-cfs-v6-rc2(*) (X @ nice -10)
> > running on a dualcore x86_64.
>
> thanks for the testing!

Very interesting indeed but fairly complicated as well.

> as a summary: i think your numbers demonstrate it nicely that the
> shorter 'timeslice length' that both CFS and SD utilizes does not have a
> measurable negative impact on your workload. To measure the total impact
> of 'timeslicing' you might want to try the exact same workload with a
> much higher 'timeslice length' of say 400 msecs, via:
>
>     echo 400000000 > /proc/sys/kernel/sched_granularity_ns  # on CFS
>     echo 400 > /proc/sys/kernel/rr_interval                 # on SD

I thought that the effective "timeslice" on CFS was double the 
sched_granularity_ns so wouldn't this make the effective timeslice double 
that of what you're setting SD to? Anyway the difference between 400 and 
800ms timeslices is unlikely to be significant so I don't mind.

-- 
-ck
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