Date: Mon, 17 Nov 2008 12:30:00 -0800 (PST)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: David Miller <davem@davemloft.net>
cc: mingo@elte.hu, dada1@cosmosbay.com, rjw@sisk.pl,
       linux-kernel@vger.kernel.org, kernel-testers@vger.kernel.org,
       cl@linux-foundation.org, efault@gmx.de, a.p.zijlstra@chello.nl,
       shemminger@vyatta.com
Subject: Re: [Bug #11308] tbench regression on each kernel release from 2.6.22
 -&gt; 2.6.28
In-Reply-To: <20081117.121641.167690467.davem@davemloft.net>
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References: <20081117184951.GA5585@elte.hu> <20081117.113936.81699150.davem@davemloft.net> <alpine.LFD.2.00.0811171149100.18283@nehalem.linux-foundation.org> <20081117.121641.167690467.davem@davemloft.net>
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On Mon, 17 Nov 2008, David Miller wrote:
> 
> It's on my workstation which is a much simpler 2 processor
> UltraSPARC-IIIi (1.5Ghz) system.

Ok. It could easily be something like a cache footprint issue. And while I 
don't know my sparc cpu's very well, I think the Ultrasparc-IIIi is super- 
scalar but does no out-of-order and speculation, no? So I could easily see 
that the indirect branches in the scheduler hurt much more, and might 
explain why the x86 profile looks so different.

One thing that non-NMI profiles also tend to show is "clumping", which in 
turn tends to rather excessively pinpoint code sequences that release the 
irq flag - just because those points show up in profiles, rather than 
being a spread-out-mush. So it's possible that Ingo's profile did show the 
scheduler more, but it was in the form of much more spread out "noise" 
rather than the single spike you saw. 

		Linus
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