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

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Message-ID: <m2tyestlcr.fsf@firstfloor.org>
Date:	Thu, 24 Mar 2011 11:38:28 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Nikanth Karthikesan <knikanth@...e.de>
Cc:	Ingo Molnar <mingo@...hat.com>, Nick Piggin <npiggin@...nel.dk>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Beulich <JBeulich@...ell.com>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] x86: avoid atomic operation in test_and_set_bit_lock if possible

Nikanth Karthikesan <knikanth@...e.de> writes:

> On x86_64 SMP with lots of CPU atomic instructions which assert the LOCK #
> signal can stall other CPUs. And as the number of cores increase this penalty

This description is very wrong. No modern CPU still has a LOCK # signal
or does global stalls for LOCK.

Do you actually have any data this is a problem and how much
difference the patch makes?

Also there's the missing barrier now of course.

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