linux-kernel - Re: Influence of optimization level, preemption and scheduler on boot time

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Date:	Tue, 22 Sep 2009 00:00:48 +1200
From:	Johannes Buchner <buchner.johannes@....at>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Influence of optimization level, preemption and scheduler on
 boot time

On Mon, 21 Sep 2009 13:20:59 +0200
Arjan van de Ven <arjan@...radead.org> wrote:

> On Mon, 21 Sep 2009 23:25:53 +1200
> Johannes Buchner <buchner.johannes@....at> wrote:
> 
> > Hi all.
> > 
> > I measured the kernel (and system) boot times while varying the
> > parameters:
> >  - Optimization level: -Os, -O2 and also -O3
> >  - Preemptive model
> >  - Scheduler: CFQ, Anticipatory, Deadline, Noop
> > 
> > My conclusion was that the optimization level and the preemptive
> > model had no significant influence on speed. CFQ let my system boot
> > several seconds faster than the other schedulers.
> > 
> > Graphs can be found at:
> > http://johannes.jakeapp.com/blog/?p=913
> > 
> > This conclusion may not be true for all situations, but I found it
> > interesting that the optimization level is so irrelevant.
> > 
> 
> it's interesting to see that the IO scheduler mattered.. 
> I would think that (s)readahead makes the IO scheduler irrelevant for
> boot time...

I did not use (s)readahead though in this measurements. Trying
readahead-list with CFQ did not bring me any improvement. Maybe, for
the other schedulers, it brings the speed on par with CFQ.


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