linux-kernel - Re: [PATCH 13/14] x86/ticketlock: add slowpath logic

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Message-ID: <4CE39AD2.9080606@goop.org>
Date:	Wed, 17 Nov 2010 01:05:22 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Avi Kivity <avi@...hat.com>
CC:	Jan Beulich <JBeulich@...ell.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Eric Dumazet <dada1@...mosbay.com>, xiyou.wangcong@...il.com,
	Peter Zijlstra <peterz@...radead.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 13/14] x86/ticketlock: add slowpath logic

On 11/17/2010 12:58 AM, Avi Kivity wrote:
>> Actually in this case I'm pretty sure there's already a "set bit"
>> function which will do the job.  set_bit(), I guess, though it takes a
>> bit number rather than a mask...
>>
>
>
> set_bit() operates on a long, while the intel manuals recommend
> against operating on operands of different size, especially with
> locked operations.  I think newer processors have more relaxed
> requirements, though.

Despite its prototype, set_bit() is pretty specifically using "orb" for
a the constant case, or bts otherwise (I don't know what size memory
operation bts is considered to generate).

    J

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