Re: [Xen-devel] VT-d Posted-interrupt (PI) design for XEN

[Tim Deegan <tim@xxxxxxx>]

At 02:07 +0000 on 06 Mar (1425604054), Wu, Feng wrote:
> > From: Tim Deegan [mailto:tim@xxxxxxx]
> > But I don't understand why we would need a new global vector for
> > RUNSTATE_blocked rather than suppressing the posted interrupts as you
> > suggest for RUNSTATE_runnable.  (Or conversely why not use the new
> > global vector for RUNSTATE_runnable too?)
> 
> If we suppress the posted-interrupts when vCPU is blocked, it cannot
> be unblocked by the external interrupts, this is not correct.

OK, I don't understand at all now. :)  When the posted interrupt is
suppressed, what happens to the interrupt?  If it's just dropped, then
we can't use that for _any_ cases.  If it goes through the old path,
via the vlapic, that should be enough to wake any HLT'ed vcpu.  It
sounds like it might be a little slower, but not necessarily once
you've had to add a new list of potentially-HLT'd-and-wakeable vcpus,
especially with many idle vcpus.

Tim.

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