Date: Fri, 7 Feb 2014 09:24:37 +0100
From: Torsten Duwe <duwe@lst.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, Anton Blanchard <anton@samba.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] Convert powerpc simple spinlocks into ticket locks
Message-ID: <20140207082437.GA26811@lst.de>
References: <20140206103736.GA18054@lst.de> <20140206163837.GT2936@laptop.programming.kicks-ass.net> <20140206173727.GA13048@lst.de> <20140206180826.GI5002@laptop.programming.kicks-ass.net>
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On Thu, Feb 06, 2014 at 07:08:26PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 06, 2014 at 06:37:27PM +0100, Torsten Duwe wrote:
> > I must admit that I haven't tested the patch on non-pseries ppc64 nor on
> > ppc32. Only ppc64 has the ldarx and I tried to atomically replace the 
> > holder along with the locks. That might prove unneccessary.
> 
> But what is the holder for? Can't we do away with that field?

Scott, Peter: good questions.
The conditional is wrong because I confused pSeries with ppc64 CPUs with
64-bit kernels. I got deluded by the LOCK_TOKEN definition above. Is that
correctly ifdef'd, with PPC64? The holder field should be ifdef'd
CONFIG_PPC_SPLPAR, independent of ppc64.

It is an advisory performance hint, and doesn't need to be updated atomically
with the lock; this and the above are 2 reasons to drop the asm string
operand size voodoo as well.

Thanks,
	Torsten

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