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

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Wed, 2015-09-23 at 06:35 +0000, Wu, Feng wrote:
> > From: George Dunlap [mailto:george.dunlap@xxxxxxxxxx]
> > On 09/22/2015 08:19 AM, Wu, Feng wrote:

> > > In the arch_block() hook, we actually need to
> > >   - Put vCPU to the blocking list
> > >   - Set the NV to wakeup vector
> > >   - Set NDST to the right pCPU
> > >   - Clear SN
> > 
> > Nit: We shouldn't need to actually clear SN here; SN should already
> > be
> > clear because the vcpu should be currently running.  (I don't think
> > there's a way for a vcpu to go from runnable->blocked, is there?) 
> >  And
> > if it's just been running, then NDST should also already be the
> > correct
> > pcpu.
> 
> Yes, we can go to blocked only from running state. let me clarify a
> question first: Xen doesn't support kernel preemption, right?
>
No, it does not.

> ( i.e. we
> can only perform context switch before returning to guest.) 
>
Yes, we schedule only when SCHEDULE_SOFTIRQ is checked and found to be
on.

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

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