Re: Interrupt time inflation on Xen

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Mar 21, 2016 at 07:10:51PM -0400, Thor Lancelot Simon wrote:
> On Sun, Mar 20, 2016 at 08:19:23PM -0400, Thor Lancelot Simon wrote:
> > 
> > I've attached the dmesg from the GENERIC kernel and the boot-time
> > messages (giving both the xen dmesg and NetBSD dmesg) from the XEN3_DOM0
> > kernel.  Xen kernel is 4.5 from pkgsrc; it is NOT a debug kernel.
> > 
> > Interrupt routing seems to be the same, disk controller is on ioapic1 pin 6
> > in both cases.
> 
> However, the Xen kernel emits:
> 
> ioapic1 at mainbus0 apid 7
> ioapic1: can't remap to apid 7
> 
> Harmless?

I think it is, as it's trying to remap to the same value (AFAIK).
But I don't know the x86 interrupt hardware that well.


> What's particularly curious here to me is that we are seeing
> twice as many interrupts as we should, in the poorly performing Xen
> case.

What controller is it ? maybe when running faster it's able
to coalesce some interrupts ?
The irq rate seems to be mostly the same in both cases, but with the
number of I/O ops cut by half in the Xen case.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--