linux-kernel - Re: [PATCH 0/7] slub: Fastpath optimization (especially for RT) V1

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Date:	Thu, 11 Dec 2014 17:50:58 +0100
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	akpm@...uxfoundation.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	linux-mm@...ck.org, penberg@...nel.org, iamjoonsoo.kim@....com,
	brouer@...hat.com
Subject: Re: [PATCH 0/7] slub: Fastpath optimization (especially for RT) V1

On Thu, 11 Dec 2014 09:03:24 -0600 (CST)
Christoph Lameter <cl@...ux.com> wrote:

> On Thu, 11 Dec 2014, Jesper Dangaard Brouer wrote:
> 
> > It looks like an impressive saving 116 -> 60 cycles.  I just don't see
> > the same kind of improvements with my similar tests[1][2].
> 
> This is particularly for a CONFIG_PREEMPT kernel. There will be no effect
> on !CONFIG_PREEMPT I hope.
> 
> > I do see the improvement, but it is not as high as I would have expected.
> 
> Do you have CONFIG_PREEMPT set?

Yes.

$ grep CONFIG_PREEMPT .config
CONFIG_PREEMPT_RCU=y
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_PREEMPT_NONE is not set
# CONFIG_PREEMPT_VOLUNTARY is not set
CONFIG_PREEMPT=y
CONFIG_PREEMPT_COUNT=y

Full config here:
 http://people.netfilter.org/hawk/kconfig/config01-slub-fastpath01

I was expecting to see at least (specifically) 4.291 ns improvement, as
this is the measured[1] cost of preempt_{disable,enable] on my system.

[1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/time_bench_sample.c
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer
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