Re: [Xen-devel] [v3 12/15] vmx: posted-interrupt handling when vCPU is blocked

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Thu, 2015-07-02 at 08:58 +0000, Wu, Feng wrote:

> > -----Original Message-----
> > From: Dario Faggioli [mailto:dario.faggioli@xxxxxxxxxx]
> >
> > This is the third time that I ask:
> >  (1) whether it is possible to have more vcpus queued on one pcpu PI
> >      blocked list with desc.on (I really believe it is);
> 
> I think it is, please see the following scenario:
> 
> When cpu masks the interrupts, and an external interrupt occurs for the
> assigned device while the target vCPU2 is blocked, the wakeup notification
> event handler has no chance to run, after a while, another wakeup
> notification event for vCPU4 blocking on the same pCPU occurs,
> after cpu unmakes the interrupts, wakeup notification handler
> gets called. Then we get:
>       vCPU2, desc.on = 1 and vCPU4, desc.on = 1
> Then in the handler we need to kick both of them.
> 
Ok, first of all, thanks for answering! :-)

And yes, this makes sense.

> >  (2) if yes, whether it is TheRightThing(TM) to kick all of them, as
> >      soon as any notification arrives, instead that putting together a
> >      mechanism for kicking only a specific one.
> > 
> Why can't we kick all of them, 'desc.on = 1' means there is a pending
> interrupt, when we meet this condition, kicking the related vCPU should
> be the right thing to do.
> 
Right, I see it now. I felt like I was missing something, and that's why
I was asking to you to elaborate a bit more.
Thanks again for having done this. I was missing/forgetting half of the
way desc.on is actually handled, sorry for this.

BTW, I'm finding it hard reading this series from the archives; there
appears to be some threading issues and some missing messages. I also
don't have it in my inbox, because my filters failed to spot and flag it
properly. If you send a new version, please, Cc me, so it will be easier
for me to look at all the patches, and provide a more helpful review.

Thanks and Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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