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

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 13/14] x86/ticketlock: add slowpath logic
From: Avi Kivity <avi@xxxxxxxxxx>
Date: Wed, 17 Nov 2010 10:58:22 +0200
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 10:52 AM, Jeremy Fitzhardinge wrote:
On 11/17/2010 12:31 AM, Jan Beulich wrote:
>>>>  On 16.11.10 at 22:08, Jeremy Fitzhardinge<jeremy@xxxxxxxx>  wrote:
>>  +static inline void __ticket_enter_slowpath(struct arch_spinlock *lock)
>>  +{
>>  +     if (sizeof(lock->tickets.tail) == sizeof(u8))
>>  +             asm (LOCK_PREFIX "orb %1, %0"
>>  +                  : "+m" (lock->tickets.tail)
>>  +                  : "i" (TICKET_SLOWPATH_FLAG) : "memory");
>>  +     else
>>  +             asm (LOCK_PREFIX "orw %1, %0"
>>  +                  : "+m" (lock->tickets.tail)
>>  +                  : "i" (TICKET_SLOWPATH_FLAG) : "memory");
>>  +}
>  Came only now to mind: Here and elsewhere, did you try using
>  %z0 to have gcc produce the opcode suffix character, rather
>  than having these somewhat ugly if()-s?

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.

error compiling committee.c: too many arguments to function

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