linux-kernel - Re: [PATCH RFC] x86: avoid atomic operation in test_and_set_bit

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Message-ID: <20110324205038.GA2393@elte.hu>
Date:	Thu, 24 Mar 2011 21:50:38 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Jack Steiner <steiner@....com>, Jan Beulich <JBeulich@...ell.com>,
	Borislav Petkov <bp@...64.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...nel.dk>,
	"x86@...nel.org" <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>, tee@....com,
	Nikanth Karthikesan <knikanth@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH RFC] x86: avoid atomic operation in test_and_set_bit_lock
 if possible


* Andi Kleen <andi@...stfloor.org> wrote:

> Ingo Molnar <mingo@...e.hu> writes:
> >
> > One good way to see cache bounces is to run a misses/accesses ratio profile:
> >
> >    perf top -e cache-misses -e cache-references --count-filter 10
> >
> > Note the two events: this runs a 'weighted' profile, you'll see (LLC) 
> > cache-misses of a function relative to cache-references it does, a 
> > misses/references ratio in essence.
> 
> If anyone does this on a Nehalem please only use 2.6.39-rc*+ which
> includes the offcore patches. Anything before that will get you complete
> bogus numbers.

In that case the second example i quoted can be used:

  perf top -e L1-dcache-store-misses -e L1-dcache-stores --count-filter 10

Or:

  perf top -e L1-dcache-load-misses -e L1-dcache-loads --count-filter 10

Thanks,

	Ingo
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