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

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Message-ID: <m2sjucl0a6.fsf@firstfloor.org>
Date:	Thu, 24 Mar 2011 13:40:49 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
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\@kernel.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\@vger.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

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.

BTW with Lin-Ming's memory latency profiling code you can do this much
more directly.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only
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