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Date: Wed, 17 Nov 2010 01:05:22 -0800
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: Avi Kivity <avi@redhat.com>
CC: Jan Beulich <JBeulich@novell.com>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        Eric Dumazet <dada1@cosmosbay.com>, xiyou.wangcong@gmail.com,
        Peter Zijlstra <peterz@infradead.org>, Nick Piggin <npiggin@kernel.dk>,
        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        Xen-devel <xen-devel@lists.xensource.com>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 13/14] x86/ticketlock: add slowpath logic
References: <cover.1289940821.git.jeremy.fitzhardinge@citrix.com><cover.1289940821.git.jeremy.fitzhardinge@citrix.com> <97ed99ae9160bdb6477284b333bd6708fb7a19cb.1289940821.git.jeremy.fitzhardinge@citrix.com> <4CE3A1060200007800022B04@vpn.id2.novell.com> <4CE397C8.9040901@goop.org> <4CE3992E.2070406@redhat.com>
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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).

    J