Re: [Xen-devel] Fwd: [v3 14/15] Update Posted-Interrupts Descriptor during vCPU scheduling

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Thu, Jul 9, 2015 at 4:09 AM, Wu, Feng <feng.wu@xxxxxxxxx> wrote:
>> That does not necessarily means "we need to do something" in
>> vcpu_runstate_change(). Actually, that's exactly what I'm asking: can
>> you check whether this thing that you need doing can be done somewhere
>> else than in vcpu_runstaete_change() ?
>
> Why do you think vcpu_runstaete_change() is not the right place to do this?

Because what the vcpu_runstate_change() function does at the moment is
*update the vcpu runstate variable*.  It doesn't actually change the
runstate -- the runstate is changed in the various bits of code that
call it; and it's not designed to be a generic place to put hooks on
the runstate changing.

I haven't done a thorough review of this yet, but at least looking
through this patch, and skimming the titles, I don't see anywhere you
handle migration -- what happens if a vcpu that's blocked / offline /
runnable migrates from one cpu to another?  Is the information
updated?

The right thing to do in this situation is either to change
vcpu_runstate_change() so that it is the central place to make all (or
most) hooks happen; or to add a set of architectural hooks (similar to
the SCHED_OP() hooks) in the various places you need them.

I'm inclined to think that the second is the better option; if for no
other reason that it makes it more clear which states are handled.

 -George

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