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 for <linuxppc-dev@lists.ozlabs.org>; Fri,  7 Feb 2014 21:45:39 +1100 (EST)
Date: Fri, 7 Feb 2014 11:45:30 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Torsten Duwe <duwe@lst.de>
Subject: Re: [PATCH] Convert powerpc simple spinlocks into ticket locks
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Cc: Tom Musta <tommusta@gmail.com>, linux-kernel@vger.kernel.org,
 Paul Mackerras <paulus@samba.org>, Anton Blanchard <anton@samba.org>,
 Scott Wood <scottwood@freescale.com>,
 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, linuxppc-dev@lists.ozlabs.org,
 Ingo Molnar <mingo@kernel.org>
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On Fri, Feb 07, 2014 at 11:31:39AM +0100, Peter Zijlstra wrote:
> Anyway, what might work is something like (please forgive my ppc asm, I
> can barely read the thing, I've never before attempted writing it):
> 
> lock:
> 1:	lharx	%0, 0, &head
> 	mov	%1, %0
> 	addic	%0, %0, 1
> 	stwcd   %0, 0, &head
> 	bne-	1b
> 2:	lhax	%0, 0, &tail

That might need to be lhz too, I'm confused on all the load variants.

> 	lwsync
> 	cmp	0, %0, %0

	cmp	0, %0, %1

So we compare the &tail load to the xadd return %1 above.

> 	bne-	2b
> 
> 
> unlock:
> 	lhz	%0, 0, &tail
> 	addic	%0, %0, 1
> 	lwsync
> 	sth	%0, 0, &tail
>