linux-kernel - Re: Mainline kernel OLTP performance update

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Date:	Wed, 29 Apr 2009 18:25:36 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Styner, Douglas W" <douglas.w.styner@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Tripathi, Sharad C" <sharad.c.tripathi@...el.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"Kleen, Andi" <andi.kleen@...el.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Ma, Chinang" <chinang.ma@...el.com>,
	"Wang, Peter Xihong" <peter.xihong.wang@...el.com>,
	"Nueckel, Hubert" <hubert.nueckel@...el.com>,
	"Recalde, Luis F" <luis.f.recalde@...el.com>,
	"Nelson, Doug" <doug.nelson@...el.com>,
	"Cheng, Wu-sun" <wu-sun.cheng@...el.com>,
	"Prickett, Terry O" <terry.o.prickett@...el.com>,
	"Shunmuganathan, Rajalakshmi" <rajalakshmi.shunmuganathan@...el.com>,
	"Garg, Anil K" <anil.k.garg@...el.com>,
	"Chilukuri, Harita" <harita.chilukuri@...el.com>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Mainline kernel OLTP performance update

On Wed, 2009-04-29 at 09:07 -0700, Andrew Morton wrote:
> On Wed, 29 Apr 2009 08:48:19 -0700 "Styner, Douglas W" <douglas.w.styner@...el.com> wrote:
> 
> > >-----Original Message-----
> > >From: Andrew Morton [mailto:akpm@...ux-foundation.org]
> > >Sent: Wednesday, April 29, 2009 12:30 AM
> > >To: Styner, Douglas W
> > >Cc: linux-kernel@...r.kernel.org; Tripathi, Sharad C;
> > >arjan@...ux.intel.com; Wilcox, Matthew R; Kleen, Andi; Siddha, Suresh B;
> > >Ma, Chinang; Wang, Peter Xihong; Nueckel, Hubert; Recalde, Luis F; Nelson,
> > >Doug; Cheng, Wu-sun; Prickett, Terry O; Shunmuganathan, Rajalakshmi; Garg,
> > >Anil K; Chilukuri, Harita; chris.mason@...cle.com
> > >Subject: Re: Mainline kernel OLTP performance update
> > >
> > >On Tue, 28 Apr 2009 10:08:22 -0700 "Styner, Douglas W"
> > ><douglas.w.styner@...el.com> wrote:
> > >
> > >> Summary: Measured the mainline kernel from kernel.org (2.6.30-rc3).
> > >>
> > >> The regression for 2.6.30-rc3 against the baseline, 2.6.24.2 is 1.91%.
> > >Oprofile reports 71.1626% user, 28.8295% system.
> > >>
> > >> Linux OLTP Performance summary
> > >> Kernel#            Speedup(x)   Intr/s  CtxSw/s us%     sys%    idle%
> > >iowait%
> > >> 2.6.24.2                1.000   22106   43709   75      24      0       0
> > >> 2.6.30-rc3              0.981   30645   43027   75      25      0       0
> > >
> > >The main difference there is the interrupt frequency.  Do we know which
> > >interrupt source(s) caused this?
> >
> > Our analysis of the interrupts shows that rescheduling interrupts are
> > up 2.2x from 2.6.24.2 --> 2.6.30-rc3.  Qla2xxx interrupts are roughly
> > the same.
> 
> (top-posting repaired)
> 
> OK, thanks.  Seems odd that the rescheduling interrupt rate increased
> while the context-switch rate actually fell a couple of percent.
> 
> This came up a few weeks ago and iirc Peter was mainly involved, and I
> don't believe that anything conclusive ended up happening.  Peter,
> could you please remind us of (and summarise) the story here?

I've had several reports about the resched-ipi going in overdrive, but
nobody bothered to bisect it, nor have I yet done so -- no clear ideas
on why it is doing so.

I'll put it somewhere higher on the todo list.

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