linux-kernel - Re: [ck] [REPORT] cfs-v5 vs sd-0.46

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Message-Id: <200704260810.38571.mgd@technosis.de>
Date:	Thu, 26 Apr 2007 08:10:24 +0200
From:	Michael Gerdau <mgd@...hnosis.de>
To:	Con Kolivas <kernel@...ivas.org>
Cc:	ck@....kolivas.org, linux-kernel@...r.kernel.org,
	Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bill Davidsen <davidsen@....com>,
	Juliusz Chroboczek <jch@....jussieu.fr>,
	Mike Galbraith <efault@....de>,
	Peter Williams <pwil3058@...pond.net.au>,
	William Lee Irwin III <wli@...omorphy.com>,
	Willy Tarreau <w@....eu>,
	Gene Heskett <gene.heskett@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [ck] [REPORT] cfs-v5 vs sd-0.46

> > with cfs-v5 finally booting on my machine I have run my daily
> > numbercrunching jobs on both cfs-v5 and sd-0.46, 2.6.21-v7 on
> > top of a stock openSUSE 10.2 (X86_64).
> 
> Thanks for testing.

I actually enjoyed it -- the more extensive test I had promised
two days ago is almost finished. There is just one test I have
yet to (re)run and I will have a slot for it later today so I'll
mail out the results 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)
during the early afternoon (my time).

> You have 3 tasks and only 2 cpus. The %cpu is the percentage of the cpu the 
> task is currently on that it is using; it is not the percentage of 
> the "overall cpu available on the machine". Since you have 3 tasks and 2 
> cpus, the extra task will always be on one or the other cpu taking half of 
> the cpu but never on both cpus.

I had assumed that given the interval of 3 sec the three tasks would
be evenly distributed among the 2 CPUs thus resulting in a CPU% of
66 each because that's what they get in the long run anyway.

Apparently 3 sec is too short an interval to see this.

> What is important is that if all three tasks are fully cpu bound and started 
> at the same time at the same nice level, that they all receive close to the 
> same total cpu time overall showing some fairness is working as well. This 
> should be the case no matter how many cpus you have.

They are started via 'make -j3' which implies they start at the
same time (i.e. within a few msec). They initially load some data
and then perform extensive computations on that data.

Best,
Michael
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