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    SubjectRe: [PATCH v8 0/6] kvm: level irqfd support
    On Thu, Aug 16, 2012 at 07:29:40PM +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.

    Exactly. So 1 ID for userspace and 1 for irqfd.

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


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