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. -- error compiling committee.c: too many arguments to function -- 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
