linux-kernel - Re: [PATCH v2 1/2] mm/slub: optimize alloc/free fastpath by removing preemption on/off

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Date:	Thu, 15 Jan 2015 23:07:49 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 1/2] mm/slub: optimize alloc/free fastpath by
 removing preemption on/off

On Thu, 15 Jan 2015 21:57:58 -0600 (CST)
Christoph Lameter <cl@...ux.com> wrote:

> > I get:
> >
> > 		mov    %gs:0x18(%rax),%rdx
> >
> > Looks to me that %gs is used.
> 
> %gs is used as a segment prefix. That does not add significant cycles.
> Retrieving the content of %gs and loading it into another register
> would be expensive in terms of cpu cycles.

OK, maybe that's what I saw in my previous benchmarks. Again, that was
a while ago.

-- Steve
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