Re: Mainline kernel OLTP performance update

[Peter Zijlstra]

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@xxxxxxxxx> wrote:
> 
> > >-----Original Message-----
> > >From: Andrew Morton [mailto:akpm@xxxxxxxxxxxxxxxxxxxx]
> > >Sent: Wednesday, April 29, 2009 12:30 AM
> > >To: Styner, Douglas W
> > >Cc: linux-kernel@xxxxxxxxxxxxxxx; Tripathi, Sharad C;
> > >arjan@xxxxxxxxxxxxxxx; 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@xxxxxxxxxx
> > >Subject: Re: Mainline kernel OLTP performance update
> > >
> > >On Tue, 28 Apr 2009 10:08:22 -0700 "Styner, Douglas W"
> > ><douglas.w.styner@xxxxxxxxx> 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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