Date: Tue, 28 Aug 2007 09:34:03 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Boldi <a1426z@gawab.com>
cc: Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>,
       Mike Galbraith <efault@gmx.de>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Subject: Re: CFS review
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On Tue, 28 Aug 2007, Al Boldi wrote:
> 
> I like your analysis, but how do you explain that these stalls vanish when 
> __update_curr is disabled?

It's entirely possible that what happens is that the X scheduling is just 
a slightly unstable system - which effectively would turn a small 
scheduling difference into a *huge* visible difference.

And the "small scheduling difference" might be as simple as "if the 
process slept for a while, we give it a bit more CPU time". And then you 
get into some unbalanced setup where the X scheduler makes it sleep even 
more, because it fills its buffers.

Or something. I can easily see two schedulers that are trying to 
*individually* be "fair", fighting it out in a way where the end result is 
not very good.

I do suspect it's probably a very interesting load, so I hope Ingo looks 
more at it, but I also suspect it's more than just the kernel scheduler.

		Linus
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