RE: [Xen-ia64-devel] vIOSAPIC and IRQs delivery

["Dong, Eddie" <eddie.dong@xxxxxxxxx>]

Tristan:
        Like mentioned in your early emails, you also agree the idea
approach should use
event channel. I am assuming you are still sticking on this, and let us
work out the idea design now.

        Then the question is:
                1: How can we get a patch for the idea design? If it
takes us 1 month, is it worth to doing now?
                My answer is yes, because event channel based approach
is most efficient and well tested in Xen. 
Also keeping consistant with Xen architecture in IRQ virtualization will
save future maintaince effort.

                2: Before the idea patch comes up, should we accept the
previous intermediate patch?
                I am tentative on this as I didn't see obvious value
here but pay some regression effort
 as it will be eventually replaced.

                3: Without the intermediate patch, can we run SMP guest?
                My answer is yes at least for Xen0. Current approach
(dom0 own machine
 IOSAPIC should be OK for 1-2 month) will not block those ongoing
effort. vIRQ stuff is a cleanup 
for future driver domain support.

        See my comments embedded too.

>> So should we use a new term virtual IRQ or interrupt virtualization?
> We can use vIRQ, which is different from VIRQ.
> 
>> Both LSAPIC and IOSAPIC need to be done in vIRQ. Sure.
> 
>> BTW, RTE is still accessed by para-guest in previous patch :-)
> Not directly, through Xen.
> Do you really think x86 para-guest doesn't program io_apic ?
No, I mean part of its function can be moved to event channel especially
for run time stuff.
Accessing those entries at run time (each time when a guest handle the
PIRQ) using hypercall
is extremely expansive IMO for example a gigabyte ethernet card. We
really need to avoid this.

> Again, you need to set up RTEs.
Yes, but no interrupt handling time mask and unmask, all those operation
can be replaced
 by event channel mask and unmask.

> Furthermore, I think we don't want to break transparent
> virtualization, so it won't be only drag and drop.

Yes, the idea approach doesn't violate transparent virtualization too.

> BTW, I think it will be *very* hard to find an ia64 platform which
> can share an IRQ line.  Maybe I am wrong but I don't know such a
> platform :-( 
I don't know exactly IA64 HW implementation, but usually an level
triggered IRQ can be 
shared by multiple devices.  Any clarification, Tony (if you are
online)?

Eddie

_______________________________________________
Xen-ia64-devel mailing list
Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-ia64-devel