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

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Message-ID: <1421415659.11734.131.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 16 Jan 2015 05:40:59 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	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, 2015-01-15 at 23:07 -0500, Steven Rostedt wrote:
> 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.

I made same observation about 3 years ago, on old cpus.


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