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

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 13/14] x86/ticketlock: add slowpath logic
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Wed, 17 Nov 2010 00:52:24 -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>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, xiyou.wangcong@xxxxxxxxx, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>
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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...

But, yes, %z0 sounds interesting.  Is it documented anywhere?  I think
I've tried to use it in the past and run into gcc bugs.


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