linux-kernel - Re: [patch 1/4] x86: FIFO ticket spinlocks

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Message-ID: <20071103034146.GA9699@wotan.suse.de>
Date:	Sat, 3 Nov 2007 04:41:46 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 1/4] x86: FIFO ticket spinlocks

On Fri, Nov 02, 2007 at 08:56:46PM -0400, Chuck Ebbert wrote:
> On 11/02/2007 07:01 PM, Nick Piggin wrote:
> > 
> > In the contended multi-threaded tight loop, the xchg lock is slower than inc
> > lock but still beats the fair xadd lock, but that's only because it is
> > just as unfair if not more so on this hardware (runtime difference of up to
> > about 10%)
> > 
> 
> I meant xchg for unlock, not lock.

That is for unlock. 2x the number of atomic operations ~= 2x the cost.

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