linux-kernel - Re: [Bug #11308] tbench regression on each kernel release from 2.6.22 -> 2.6.28

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Message-ID: <20081117224751.GA19905@elte.hu>
Date:	Mon, 17 Nov 2008 23:47:51 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
Cc:	dada1@...mosbay.com, rjw@...k.pl, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org, cl@...ux-foundation.org,
	efault@....de, a.p.zijlstra@...llo.nl,
	torvalds@...ux-foundation.org
Subject: Re: [Bug #11308] tbench regression on each kernel release from
	2.6.22 -&gt; 2.6.28

* David Miller <davem@...emloft.net> wrote:

> From: Ingo Molnar <mingo@...e.hu>
> Date: Mon, 17 Nov 2008 17:11:35 +0100
> 
> > Ouch, +4% from a oneliner networking change? That's a _huge_ speedup 
> > compared to the things we were after in scheduler land.
> 
> The scheduler has accounted for at least %10 of the tbench 
> regressions at this point, what are you talking about?

yeah, you are probably right when it comes to task migration policy 
impact - that can have effects in that range. (and that, you have to 
accept, is a fundamentally hard and fragile job to get right, as it 
involves observing the past and predicting the future out of it - at 
1.3 million events per second)

So above i was just talking about straight scheduling code overhead. 
(that cannot have been +10% of the total - as the whole scheduler only 
takes 7% total - TLB flush and FPU restore overhead included. Even the 
hrtimer bits were about 1% of the total.)

	Ingo
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