Re: [Xen-devel] Interrupt Affinity Question

["Pradeep Vincent" <pradeep.vincent@xxxxxxxxx>]

Wouldn't it be better to set dom0_vcpus_pin by default when dom0 is
handling all the I/O. dom0 clearly should have high priority (weight)
to avoid excessive I/O latency and hence none of the dom-0 vcpu would
be left waiting in the runq for too long.

Only problem would be relatively rare schedule-latency hit due to lack
of ability to migrate but I am wondering if this would be better
trade-off.

Thanks Keir,

- Pradeep Vincent


On 4/13/07, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:
> On 14/4/07 04:33, "Pradeep Vincent" <pradeep.vincent@xxxxxxxxx> wrote:
>
> > If dom-0 vcpu to pcpu affinity is not set (dom0_vcpus_pin not set),
> > what happens when dom-0 vcpu migrates - is the  processor affinity of
> > the irq channels changed by some means to reflect the migration  or do
> > the hardware interrupts end up going to the old processor while the
> > pirq will be served by the dom-0 vcpu on a different processor ?
>
> This doesn't happen right now. What we may need to do is measure the cost of
> needing to forward the interrupt to the correct CPU, in the case that the
> VCPU is currently running on a different CPU, versus the cost of
> reprogramming an IOAPIC register. Also important is to know how rapidly the
> credit scheduler is moving VCPUs among CPUs, and hence the average number of
> interrupts between movements.
>
>  -- Keir
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel