RE: [Xen-devel] [PATCH] Dont' round-robin the callback interrupt

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

Just to be clear. I'm only modifying the behavior of the irq being used for 
callback, so this should not affect pass through devices.

  Paul

> -----Original Message-----
> From: Keir Fraser
> Sent: 12 July 2010 18:41
> To: Keir Fraser; Paul Durrant; xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: Tim Deegan; Juergen Gross
> Subject: Re: [Xen-devel] [PATCH] Dont' round-robin the callback
> interrupt
> 
> On 12/07/2010 18:17, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
> wrote:
> 
> >>   However, that's not the motivation for this patch. In the
> windows code, we
> >> only bind event channels to vcpu 0 since we cannot get callback
> interrupts on
> >> multiple vcpus simultaneously, since the interrupt is level
> sensitive. Thus
> >> round-robining is wasteful in terms of kicking certain data
> structures
> >> between
> >> caches (assuming a reasonably constant vcpu -> pcpu mapping).
> >
> > Surely that argument can be made for any interrupt that is set up
> to
> > round-robin among multiple CPUs? Obviously in the PV drivers case
> the
> > event-channel IRQ is probably the only significant source of
> round-robin
> > interrupts. But I don't see that it's special in any other way.
> 
> Further, the correct semantics for LowestPrio delivery was
> implemented by
> Juergen Gross at Fujitsu for a reason. Cc'ing him. I suspect he will
> say
> that relaxing the delivery semantics will cause something he cares
> about to
> break.
> 
>  -- Keir
> 


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