Re: [Xen-devel] [PATCH v6 15/18] vmx: Properly handle notification event when vCPU is running

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

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, September 08, 2015 5:31 PM
> To: Wu, Feng
> Cc: Andrew Cooper; Tian, Kevin; Zhang, Yang Z; xen-devel@xxxxxxxxxxxxx; Keir
> Fraser
> Subject: RE: [PATCH v6 15/18] vmx: Properly handle notification event when
> vCPU is running
> 
> >>> On 08.09.15 at 11:23, <feng.wu@xxxxxxxxx> wrote:
> 
> >>
> >> Now that you say it, this looks even more odd: Why would you need
> >> to raise that softirq if the only way to come here is via the triggering
> >> in __vmx_deliver_posted_interrupt() (which already raised that
> >> softirq)? I suppose I must be missing something...
> >
> > Before VT-d PI, __vmx_deliver_posted_interrupt() is the only way
> > to trigger interrupt with vector ' posted_intr_vector ', but after
> > introducing VT-d PI, VT-d hardware can issue the interrupt with
> > that vector as well. In __vmx_deliver_posted_interrupt(), it set
> > the softirqs, the reason of which is described in the comments
> > of pi_notification_interrupt(), however, I need do the same thing
> > when VT-d hardware issue the interrupt, so pi_notification_interrupt()
> > is the proper place to do it.
> 
> But again - my main concern is about the !iommu_intpost case: What
> good does the raising of the softirq there? (As a general remark -
> please, when you add code to support a new feature, don't just
> think about the case where the new feature is available in hardware,
> but also about the case where it's not. While over time the set of
> systems lacking the feature will likely decrease, initially it may be the
> vast majority of systems Xen gets run on which would get penalized.)

No problem. Two solutions:
#1, Register pi_notification_interrupt when iommu_intpost and still
use event_check_interrupt in the !iommu_intpost case.
#1, Use pi_notification_interrupt() for both iommu_intpost and
!iommu_intpost, add the following check it:
        if ( iommu_intpost )
                raise_softirq(VCPU_KICK_SOFTIRQ);

Which one do you prefer?

Thanks,
Feng


> 
> Jan


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