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

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Date:	Wed, 18 Apr 2007 10:55:25 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andy Whitcroft <apw@...dowen.org>, 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>,
	Steve Fox <drfickle@...ibm.com>,
	Nishanth Aravamudan <nacc@...ibm.com>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

On Tue, Apr 17, 2007 at 11:59:00AM +0200, Ingo Molnar wrote:
> 
> * Nick Piggin <npiggin@...e.de> wrote:
> 
> > 2.6.21-rc7-cfs-v2
> > 534.80user 30.92system 2:23.64elapsed 393%CPU
> > 534.75user 31.01system 2:23.70elapsed 393%CPU
> > 534.66user 31.07system 2:23.76elapsed 393%CPU
> > 534.56user 30.91system 2:23.76elapsed 393%CPU
> > 534.66user 31.07system 2:23.67elapsed 393%CPU
> > 535.43user 30.62system 2:23.72elapsed 393%CPU
> 
> Thanks for testing this! Could you please try this also with:
> 
>    echo 100000000 > /proc/sys/kernel/sched_granularity

507.68user 31.87system 2:18.05elapsed 390%CPU
507.99user 31.93system 2:18.09elapsed 390%CPU
507.46user 31.78system 2:18.03elapsed 390%CPU
507.68user 31.93system 2:18.11elapsed 390%CPU
507.63user 31.98system 2:18.01elapsed 390%CPU
507.83user 31.94system 2:18.28elapsed 390%CPU

> could you maybe even try a more extreme setting of:
> 
>    echo 500000000 > /proc/sys/kernel/sched_granularity

504.87user 32.13system 2:18.03elapsed 389%CPU
505.94user 32.29system 2:17.87elapsed 390%CPU
506.10user 31.90system 2:17.96elapsed 389%CPU
505.02user 32.02system 2:17.96elapsed 389%CPU
506.69user 31.96system 2:17.82elapsed 390%CPU
505.70user 31.84system 2:17.90elapsed 389%CPU


Again, for comparison 2.6.21-rc7 mainline:

508.87user 32.47system 2:17.82elapsed 392%CPU
509.05user 32.25system 2:17.84elapsed 392%CPU
508.75user 32.26system 2:17.83elapsed 392%CPU
508.63user 32.17system 2:17.88elapsed 392%CPU
509.01user 32.26system 2:17.90elapsed 392%CPU
509.08user 32.20system 2:17.95elapsed 392%CPU

So looking at elapsed time, a granularity of 100ms is just behind the
mainline score. However it is using slightly less user time and
slightly more idle time, which indicates that balancing might have got
a bit less aggressive.

But anyway, it conclusively shows the efficiency impact of such tiny
timeslices.
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