linux-kernel - Re: [RFC patch] CFS fix place entity spread issue (v2)

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Message-ID: <alpine.LFD.2.00.1004181317100.14500@i5.linux-foundation.org>
Date:	Sun, 18 Apr 2010 13:21:13 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <greg@...ah.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jarkko Nikula <jhnikula@...il.com>,
	Tony Lindgren <tony@...mide.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC patch] CFS fix place entity spread issue (v2)

On Sun, 18 Apr 2010, Mathieu Desnoyers wrote:
>
> CFS fix place entity spread issue (v2)
> 
> Huge CFS vruntime spread (18 minutes) has been observed with LTTng while simply
> running Xorg on a uniprocessor machine. Detailed explanation in my ELC2010
> presentation at:

Hmm. I tested this patch with my favourite non-scientific desktop load 
test: do web browsing while doing a kernel compile with "make -j16" (after 
doing a "git clean -dqfx" and "ccache -C" to get rid of old object files 
and ccache).

This is on a dual-core (with SMT, so 4 threads) Core i5, so "make -j16" 
overcommits the CPU's quite a bit.

And quite frankly, I think your patch makes things much worse. I don't 
have numbers, but it felt much choppier and slower to do scrolling in 
firefox o moving windows around while the load average is 20+.

My testload is in no way objective, nor necessarily any good, but it's the 
one I happen to use, and while it's subjective, I think the difference was 
pretty clear and not good.

			Linus
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