Re: Mainline kernel OLTP performance update

James Bottomley
2009-01-15T14:12:46Z

On Wed, 2009-01-14 at 18:04 -0800, Andrew Morton wrote:
> On Wed, 14 Jan 2009 18:21:47 -0700 Matthew Wilcox <matthew@wil.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