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

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Date:	Wed, 17 Nov 2010 11:10:48 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
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 11:05 AM, Jeremy Fitzhardinge wrote:
> 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).
>

Perhaps that should be fixed.

bts will take its size from the argument, so it will be a btsq on 
x86_64.  AFAICT, the only visible difference between btsl and btsq is a 
page fault if the last four bytes of the operand are in an unmapped page.

-- 
error compiling committee.c: too many arguments to function

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