linux-kernel - Re: Mainline kernel OLTP performance update

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Date:	Thu, 15 Jan 2009 09:12:46 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Matthew Wilcox <matthew@....cx>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	chinang.ma@...el.com, linux-kernel@...r.kernel.org,
	sharad.c.tripathi@...el.com, arjan@...ux.intel.com,
	andi.kleen@...el.com, suresh.b.siddha@...el.com,
	harita.chilukuri@...el.com, douglas.w.styner@...el.com,
	peter.xihong.wang@...el.com, hubert.nueckel@...el.com,
	chris.mason@...cle.com, srostedt@...hat.com,
	linux-scsi@...r.kernel.org,
	Andrew Vasquez <andrew.vasquez@...gic.com>,
	Anirban Chakraborty <anirban.chakraborty@...gic.com>
Subject: Re: Mainline kernel OLTP performance update

On Wed, 2009-01-14 at 18:04 -0800, Andrew Morton wrote:
> On Wed, 14 Jan 2009 18:21:47 -0700 Matthew Wilcox <matthew@....cx> wrote:
> > On Wed, Jan 14, 2009 at 04:35:57PM -0800, Andrew Morton wrote:
> > > > > Linux OLTP Performance summary
> > > > > Kernel#            Speedup(x)   Intr/s  CtxSw/s us%  sys%   idle%  iowait%
> > > > > 2.6.24.2                1.000   21969   43425   76   24     0      0
> > > > > 2.6.27.2                0.973   30402   43523   74   25     0      1
> > > > > 2.6.29-rc1              0.965   30331   41970   74   26     0      0
> > 
> > > But the interrupt rate went through the roof.
> > 
> > Yes.  I forget why that was; I'll have to dig through my archives for
> > that.
> 
> Oh.  I'd have thought that this alone could account for 3.5%.

Me too.  Anecdotally, I haven't noticed this in my lab machines, but
what I have noticed is on someone else's laptop (a hyperthreaded atom)
that I was trying to demo powertop on was that IPI reschedule interrupts
seem to be out of control ... they were ticking over at a really high
rate and preventing the CPU from spending much time in the low C and P
states.  To me this implicates some scheduler problem since that's the
primary producer of IPI reschedules ... I think it wouldn't be a
significant extrapolation to predict that the scheduler might be the
cause of the above problem as well.

James


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