On Thu, Jun 28, 2012 at 11:48:40AM +0300, Michael S. Tsirkin wrote:
> On Thu, Jun 28, 2012 at 11:46:11AM +0300, Gleb Natapov wrote:
> > On Thu, Jun 28, 2012 at 11:41:05AM +0300, Michael S. Tsirkin wrote:
> > > On Thu, Jun 28, 2012 at 11:35:41AM +0300, Gleb Natapov wrote:
> > > > On Thu, Jun 28, 2012 at 11:34:35AM +0300, Michael S. Tsirkin wrote:
> > > > > On Thu, Jun 28, 2012 at 09:34:31AM +0300, Gleb Natapov wrote:
> > > > > > On Thu, Jun 28, 2012 at 01:31:29AM +0300, Michael S. Tsirkin wrote:
> > > > > > > On Wed, Jun 27, 2012 at 04:04:18PM -0600, Alex Williamson wrote:
> > > > > > > > On Wed, 2012-06-27 at 18:26 +0300, Michael S. Tsirkin wrote:
> > > > > > > > > On Tue, Jun 26, 2012 at 11:09:46PM -0600, Alex Williamson
> > > > > > > > > wrote:
> > > > > > > > > > @@ -71,6 +130,14 @@ irqfd_inject(struct work_struct *work)
> > > > > > > > > > kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID,
> > > > > > > > > > irqfd->gsi, 0);
> > > > > > > > > > }
> > > > > > > > > >
> > > > > > > > > > +static void
> > > > > > > > > > +irqfd_inject_level(struct work_struct *work)
> > > > > > > > > > +{
> > > > > > > > > > + struct _irqfd *irqfd = container_of(work, struct
> > > > > > > > > > _irqfd, inject);
> > > > > > > > > > +
> > > > > > > > > > + kvm_set_irq(irqfd->kvm, irqfd->source->id, irqfd->gsi,
> > > > > > > > > > 1);
> > > > > > > > > > +}
> > > > > > > > > > +
> > > > > > > > > > /*
> > > > > > > > > > * Race-free decouple logic (ordering is critical)
> > > > > > > > > > */
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > Why is it safe to ignore return value here?
> > > > > > > > > needs a comment.
> > > > > > > >
> > > > > > > > Well, it seems like you and Gleb came to the conclusion that
> > > > > > > > it's safe,
> > > > > > > > but I can really follow from the list thread. Can you explain
> > > > > > > > and I'll
> > > > > > > > add a comment? Thanks,
> > > > > > > >
> > > > > > > > Alex
> > > > > > >
> > > > > > > We merely talked about edge interrupts.
> > > > > > >
> > > > > > In fact it would have been nice to return -EBUSY when write() to
> > > > > > level
> > > > > > irqfd is coalesced.
> > > > >
> > > > > Possibly nice but not really practical.
> > > > >
> > > > What do you mean by that? Impossible to implement or not useful?
> > >
> > > Impossible to implement and also does not match normal eventfd
> > > semantics.
> > >
> > Hmm, I remember we discussed using irqfd for level triggered interrupt ~2
> > years ago and came to a conclusion that eventfd is a bad fit for it,
> > was true than is true now. Not be able to detect coalescing will make
> > irqfd level interrupts inferior to IRQ_LINE ioctl.
>
> This aspect isn't different from MSI though, is it?
>
For MSI delivered through irqfd it isn't, so yes, level triggered are
not more broken in this regards. You can detect coalescing if you
deliver MSI through ioctl.
--
Gleb.
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