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. > > So I'm inclined to say source IDs are a requirement for shared > interrupts. Can yo show a specific example that breaks? I don't think it can exist. > That means the re-use scheme becomes complicated (ex. we > run out of IRQ source IDs, so we start looking for sharing by re-using a > source ID used by a different GSI). Do we want to do that in kernel or > userspace? This series allows userspace to deal with that complexity. > Please let me know if I'm thinking incorrectly about source ID re-use. > Thanks, > > Alex I think there is a misunderstanding. All deassert on ack irqfds can share a source ID. This is why I am now thinking deassert on ack behaviour should be set when irqfd is assigned. > > > > They > > > can also detach and re-attach components at will. It also opens > > > up the possibility that userspace might want to use each IRQ > > > source ID for more than one GSI (and avoids the kernel needing > > > to manage that). Per suggestions, EOIFD is now IRQ_ACKFD. > > > > > > I really wanted to add a de-assert-only option to irqfd so the > > > irq_ackfd could be fed directly into an irqfd, but I'm dependent > > > on the ordering of de-assert _then_ signal an eventfd. Keeping > > > that ordering doesn't seem to be possible, especially since irqfd > > > uses a workqueue, if I attempt to make that connection. Thanks, > > > > > > Alex > > > --- > > > > > > Alex Williamson (6): > > > kvm: Add de-assert option to KVM_IRQ_ACKFD > > > kvm: KVM_IRQ_ACKFD > > > kvm: Add assert-only option to KVM_IRQFD > > > kvm: Add IRQ source ID option to KVM_IRQFD > > > kvm: Expose IRQ source IDs to userspace > > > kvm: Allow filtering of acked irqs > > > > > > > > > Documentation/virtual/kvm/api.txt | 53 ++++++ > > > arch/x86/kvm/Kconfig | 1 > > > arch/x86/kvm/i8254.c | 1 > > > arch/x86/kvm/i8259.c | 8 + > > > arch/x86/kvm/x86.c | 8 + > > > include/linux/kvm.h | 39 ++++- > > > include/linux/kvm_host.h | 18 ++ > > > virt/kvm/Kconfig | 3 > > > virt/kvm/assigned-dev.c | 1 > > > virt/kvm/eventfd.c | 315 +++++++++++++++++++++++++++++++++++++ > > > virt/kvm/ioapic.c | 5 - > > > virt/kvm/irq_comm.c | 28 +++ > > > virt/kvm/kvm_main.c | 26 +++ > > > 13 files changed, 496 insertions(+), 10 deletions(-) > > -- 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
