Re: [Xen-devel] (v2) VT-d Posted-interrupt (PI) design for XEN

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Monday, March 23, 2015 4:26 PM
> To: Wu, Feng
> Cc: Tian, Kevin; Zhang, Yang Z; xen-devel@xxxxxxxxxxxxx; Keir Fraser
> (keir@xxxxxxx)
> Subject: RE: (v2) VT-d Posted-interrupt (PI) design for XEN
> 
> >>> On 23.03.15 at 09:14, <feng.wu@xxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: Thursday, March 19, 2015 5:57 PM
> >> >>> On 18.03.15 at 13:44, <feng.wu@xxxxxxxxx> wrote:
> >> > Here are what we do for the blocked vCPU:
> >> > 1. Define a per-cpu list 'blocked_vcpu_on_cpu', which stored the blocked
> >> > vCPU on the pCPU.
> >> > 2. When the vCPU's state is changed to RUNSTATE_blocked, insert the
> vCPU
> >> > to the per-cpu list belonging to the pCPU it was running.
> >> > 3. When the vCPU is unblocked, remove the vCPU from the related pCPU
> list.
> >>
> >> And this works transparently not only with the generic scheduler
> >> code moving the vCPU to another pCPU, but also with some of the
> >> individual scheduler implementations doing such re-assignments?
> >
> > I cannot quite understand this, could you please elaborate a bit more.
> 
> There are multiple places where v->processor can get changed for a
> particular vCPU, and obviously all of these need to be taken care of.
> Yet a change like the one to come here would normally not be
> expected to touch specific schedulers' code, and hence suitably
> abstracting this may need some extra thought.
> 
> Jan

Why do we need care about the places where v->processor gets changed,
my idea about this is:

Before vCPU is blocked, we can get v->processor, and save the vCPU to
this per-CPU list. Besides that v->processor is the destination of the 
notification
event (it is stored in Posted-interrupt descriptor). So when wakeup
notification event happens form this vCPU, it goes to pCPU v->processor,
then in the wakeup notification event handler, we can find the list via
smp_processor_id(), hence find the right vCPU to wake up.

Do I miss something here? Thanks a lot!

Thanks,
Feng



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel