Re: Problem? intel_iommu=off; perf top shows acpi_os_read_port asextremely busy

[Michael Breuer]

Ok - my only question then is why things appear so different with 
intel_iommu enabled.
Arjan van de Ven wrote:
> On Sat, 28 Nov 2009 08:18:08 +0100
> Ingo Molnar <mingo@xxxxxxx> wrote:
>
>   
> > * Michael Breuer <mbreuer@xxxxxxxxxx> wrote:
> >
> >     
> > > Having given up for now on VT-D, I rebooted 2.6.38 rc8 with 
> > > intel_iommu=off. Whilst my myriad of broken bios issues cleared, I
> > > now see in perf top acpi_os_read_port as continually the busiest
> > > function. With intel_iommu enabled, _spin_lock was always on top,
> > > and nothing else was notable.
> > >
> > > This seems odd to me, perhaps this will make sense to someone else.
> > >
> > > FWIW, I'm running on an Asus p6t deluxe v2; ht enabled; no errors
> > > or oddities in dmesg or /var/log/messages.
> > >       
> > Could you post the perf top output please?
> >
> > Also, could you also post the output of:
> >
> > 	perf stat -a --repeat 10 sleep 1
> >
> > this will show us how idle the system is. (My guess is that your
> > system is idle and perf top shows acpi_os_read_port because the
> > system goes to idle via ACPI methods and PIO is slow. In that case
> > all is nominal and your system is fine. But it's hard to tell without
> > more details.)
> >
> >     
>
> yeah the os_read_port is part of the idle loop, so if your system is
> idle it'll show up big.... not much we can optimize there though...
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