On Thu, 2012-08-16 at 19:29 +0300, Avi Kivity wrote: > On 08/15/2012 10:22 PM, Michael S. Tsirkin wrote: > > On Wed, Aug 15, 2012 at 11:36:31AM -0600, Alex Williamson wrote: > >> On Wed, 2012-08-15 at 17:28 +0300, Michael S. Tsirkin wrote: > >> > On Fri, Aug 10, 2012 at 04:37:08PM -0600, Alex Williamson wrote: > >> > > v8: > >> > > > >> > > Trying a new approach. Nobody seems to like the internal IRQ > >> > > source ID object and the interactions it implies between irqfd > >> > > and eoifd, so let's get rid of it. Instead, simply expose > >> > > IRQ source IDs to userspace. This lets the user be in charge > >> > > of freeing them or hanging onto a source ID for later use. > >> > > >> > In the end it turns out source ID is an optimization for shared > >> > interrupts, isn't it? Can't we apply the optimization transparently to > >> > the user? E.g. if we have some spare source IDs, allocate them, if we > >> > run out, use a shared source ID? > >> > >> Let's think about shared source IDs a bit more. I think it's wrong that > >> irqfd uses KVM_USERSPACE_IRQ_SOURCE_ID, but I'm questioning whether all > >> irqfd users can share a source ID. We do not get the logical OR of all > >> users by putting them on the same source ID, we get "last set wins". > >> KVM_USERSPACE_IRQ_SOURCE_ID is used for multiple inputs because the > >> logical OR happens in userspace. How would we not starve a user if we > >> define KVM_IRQFD_SOURCE_ID? What am I missing? > > > > That all irqfds are deasserted on EOI anyway. So there's no point > > to do a logical OR. > > > > > > What if a level irqfd shares a line with a KVM_IRQ_LINE ioctl? Then an > EOI can de-assert the irqfd source, but the line is kept high by the > last KVM_IRQ_LINE invocation. As I understand Michael's proposal, the shared irq source id used by level-deassert-irqfds can only be asserted via an irqfd injection and can only be de-asserted by the ack notifier. If we let any other interface have access to the irq source id it breaks. If KVM_IRQ_LINE picks up and extension to specify the irq source id, it would have to be prevented from accessing this one. Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
