linux-kernel - Re: [GIT PULL] sched/core for v2.6.32

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Message-ID: <alpine.LNX.2.00.0909132349270.23341@swampdragon.chaosbits.net>
Date:	Mon, 14 Sep 2009 00:03:20 +0200 (CEST)
From:	Jesper Juhl <jj@...osbits.net>
To:	Mike Galbraith <efault@....de>
cc:	Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [GIT PULL] sched/core for v2.6.32

On Sun, 13 Sep 2009, Mike Galbraith wrote:

> On Sun, 2009-09-13 at 00:07 +0200, Jesper Juhl wrote:
> > On Sat, 12 Sep 2009, Ingo Molnar wrote:
> > 
> 
> > > It was a statistical property based on performance considerations - 
> > > and now we flipped it around based on latency and for kbuild 
> > > performance/throughput reasons: Serge Belyshev reported a 7% 
> > > increase on a quad due to this change and i measured a 1.5% 
> > > peak-kbuild performance increase.
> > > 
> > Impressive. I wouldn't have expected that much gain by running the parent 
> > first. Actually I personally would have expected child-first to perform 
> > better since (in my experience) it's usually the child that's just forked 
> > that matters the most.
> 
> How can waiting for child1 to run a bit before forking off child2 _not_
> hurt?  The parent is the worker bee creator, the queen bee if you will.
> Seems to me that making the queen wait until one egg hatches and ages a
> bit before laying another egg is a very bad plan if the goal is to have
> a hive full of short lived worker bees.
> 
When I wrote the above, I was thinking of one specific case; a server that 
receives a request, forks off a child to handle the request and the 
performance we measure is of how long it takes to handle that single 
request - and in that specific scenario we want the child to run as soon 
as possible.

-- 
Jesper Juhl <jj@...osbits.net>             http://www.chaosbits.net/
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