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

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Message-ID: <4CE397C8.9040901@goop.org>
Date:	Wed, 17 Nov 2010 00:52:24 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	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>,
	Avi Kivity <avi@...hat.com>,
	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 12:31 AM, Jan Beulich wrote:
>>>> On 16.11.10 at 22:08, Jeremy Fitzhardinge <jeremy@...p.org> 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.

Thanks,
    J
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