Re: [Xen-devel] Degregated I/O Performance since 3.4 - Regression in 3.4?

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 25 Apr 2012, Tobias Geiger wrote:
> Am Mittwoch, 25. April 2012, 15:44:44 schrieb Stefano Stabellini:
> > On Wed, 25 Apr 2012, Tobias Geiger wrote:
> > > Hi,
> > > 
> > > 9846ff10 was it!
> > > after reverting it, performance returned to normal.
> > 
> > Argh, that is one of my commits, and is supposed to be a performance
> > improvement!
> > 
> > I couldn't reproduce the regression you are seeing but the patch is
> > pretty simple, so just by reading it again I think I manage to spot a
> > possible error. Could you please try again with the appended patch?
> > 
> > 
> > 
> > diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> > index 4b33acd..0a8a17c 100644
> > --- a/drivers/xen/events.c
> > +++ b/drivers/xen/events.c
> > @@ -274,7 +274,7 @@ static unsigned int cpu_from_evtchn(unsigned int
> > evtchn)
> > 
> >  static bool pirq_check_eoi_map(unsigned irq)
> >  {
> > -   return test_bit(irq, pirq_eoi_map);
> > +   return test_bit(pirq_from_irq(irq), pirq_eoi_map);
> >  }
> > 
> >  static bool pirq_needs_eoi_flag(unsigned irq)
> 
> Looks good; 
> 
> I applied it to 3.4.0-rc4 and the performance went to normal again.

I'll add your tested-by if it is OK for you

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