Re: [Xen-devel] [PATCH v7 15/17] vmx: VT-d posted-interrupt core logic handling

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Tue, 2015-09-22 at 13:25 +0000, Wu, Feng wrote:
> 

> > -----Original Message-----
> > From: George Dunlap [mailto:george.dunlap@xxxxxxxxxx]

> Specifically, consider the following scheduling case happened on
> pCPUA:
> vCPUA --> idle --> vCPUB
> 
> 1. First, vCPUA is running on pCPUA, so the NDST filed in PI
> descriptor is pCPUA
> 2. Then vCPUA is switched out and idle is switched in running in
> pCPUA
> 3. Sometime later, vCPUB is switched in on pCPUA. However, the NDST
> field
> for vCPUA is still pCPUA, and currently, vCPUB is running on it. That
> means
> the spurious PI interrupts for vCPUA can disturb vCPUB (because the
> NDST
> field is pCPUA), it seems not so good to me.
> 
Mmm... Ok, but you're not saying what caused the transition from vCPUA
to idle, and from idle to vCPUB. That matters because, if this all
happened because blockings and wakeups, it's nothing to do with lazy
context switch, which is what we are discussing here (in the sense that
PI data structures would, in those cases, be updated appropriately in
block and wake hooks).

Also, if we're going from vCPUA to vCPUB, even if there's idle in
between, that can't be done via lazy context switch. In fact, in this
case, __context_switch() must be called at some point (during the idle-
->vCPUB switch, if my understanding is correct), and the hook will
actually get called!

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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