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Date: Fri, 27 Sep 2013 08:02:13 +0200
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and
 locking code into its own file
Message-ID: <20130927060213.GA6673@gmail.com>
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To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Jason Low <jason.low2@hp.com>, Davidlohr Bueso <davidlohr@hp.com>, Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>, Michel Lespinasse <walken@google.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Rik van Riel <riel@redhat.com>, Peter Hurley <peter@hurleysoftware.com>, linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>


* Tim Chen <tim.c.chen@linux.intel.com> wrote:

> > If we prefer to optimize this a bit though, perhaps we can first move 
> > the node->lock = 0 so that it gets executed after the "if (likely(prev 
> > == NULL)) {}" code block and then delete "node->lock = 1" inside the 
> > code block.
> 
> I suppose we can save one single assignment. The gain is probably not 
> noticeable as once we set node->next to NULL, node->locked is likely in 
> local cache line and the assignment operation is cheap.

Would be nice to have this as a separate, add-on patch. Every single 
instruction removal that has no downside is an upside!

You can add a comment that explains it.

Thanks,

	Ingo

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