linux-kernel - Re: [PATCH] Convert powerpc simple spinlocks into ticket locks

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Date:	Fri, 7 Feb 2014 11:45:30 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Torsten Duwe <duwe@....de>
Cc:	Scott Wood <scottwood@...escale.com>, linux-kernel@...r.kernel.org,
	Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	Tom Musta <tommusta@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] Convert powerpc simple spinlocks into ticket locks

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
> 
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