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[Xen-devel] Re: [PATCH 13/14] x86/ticketlock: add slowpath logic

To: Avi Kivity <avi@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 13/14] x86/ticketlock: add slowpath logic
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Wed, 17 Nov 2010 01:05:22 -0800
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, xiyou.wangcong@xxxxxxxxx, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>
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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).


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