linux-kernel - Re: [PATCH] mm: slub: Ensure that slab

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Message-ID: <20160309122217.GK6356@twins.programming.kicks-ass.net>
Date:	Wed, 9 Mar 2016 13:22:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	linux-parisc@...r.kernel, Helge Deller <deller@....de>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Pekka Enberg <penberg@...nel.org>, linux-mm@...ck.org,
	Noam Camus <noamc@...hip.com>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-snps-arc@...ts.infradead.org,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic

On Wed, Mar 09, 2016 at 05:23:26PM +0530, Vineet Gupta wrote:
> > I did not follow through the maze, I think the few archs implementing
> > this simply do not include this file at all.
> > 
> > I'll let the first person that cares about this worry about that :-)
> 
> Ok - that's be me :-) although I really don't see much gains in case of ARC LLSC.
> 
> For us, LD + BCLR + ST is very similar to LLOCK + BCLR + SCOND atleast in terms of
> cache coherency transactions !

The win would be in not having to ever retry the SCOND. Although in this
case, the contending CPU would be doing reads -- which I assume will not
cause a SCOND to fail, so it might indeed not make any difference.