linux-kernel - Re: [x86, vdso] cfda7bb9ecb: +14.7% will-it-scale.per_thread

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Date:	Thu, 22 May 2014 09:54:48 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Jet Chen <jet.chen@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org
Subject: Re: [x86, vdso] cfda7bb9ecb: +14.7% will-it-scale.per_thread_ops

Hi Andy,

On Wed, May 21, 2014 at 03:46:58PM -0700, Andy Lutomirski wrote:
> On Mon, May 19, 2014 at 10:59 PM, Jet Chen <jet.chen@...el.com> wrote:
> > Hi Andy,
> >
> > FYI, we noticed the below changes on
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/vdso
> > commit cfda7bb9ecbf9d96264bb5bade33a842966d1062 ("x86, vdso: Move syscall
> > and sysenter setup into kernel/cpu/common.c")
> 
> This is really strange.  That change shouldn't have any effect except
> that some kernels might boot a cycle or two faster.
> 
> >
> > test case: nhm4/will-it-scale/sched_yield
> >
> > 3d7ee969bffcc98  cfda7bb9ecbf9d96264bb5bad
> > ---------------  -------------------------
> >     5497021 ~ 0%     +14.7%    6303424 ~ 0%  TOTAL
> > will-it-scale.per_thread_ops
> >        0.54 ~ 0%      +5.6%       0.57 ~ 0%  TOTAL will-it-scale.scalability
> >     6209483 ~ 0%      +1.6%    6305917 ~ 0%  TOTAL
> > will-it-scale.per_process_ops
> >        2455 ~ 5%     +16.9%       2870 ~ 5%  TOTAL cpuidle.C1-NHM.usage
> >        8829 ~ 7%     +15.2%      10169 ~10%  TOTAL
> > slabinfo.kmalloc-64.active_objs
> >       24.13 ~12%     +48.9%      35.93 ~14%  TOTAL time.user_time
> >         393 ~ 0%      -3.0%        382 ~ 1%  TOTAL time.system_time
> >
> 
> Is this a speedup or a slowdown?

It's a speedup. The will-it-scale/sched_yield test case's throughput
increased by +14.7% (multi-thread case) and +1.6% (multi-process case).

However the CPU %user time increased more, by +48.9%.

Thanks,
Fengguang
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