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    SubjectRe: [PATCH RFC] kvm: enable irq injection from interrupt context
    On Thu, Sep 16, 2010 at 05:43:26PM +0200, Gleb Natapov wrote:
    > On Thu, Sep 16, 2010 at 05:24:11PM +0200, Michael S. Tsirkin wrote:
    > > On Thu, Sep 16, 2010 at 04:51:17PM +0200, Gleb Natapov wrote:
    > > > > > What for? Device emulation should do de-assert.
    > > > >
    > > > > Sorry, but at this point I have no idea what you call device emulation.
    > > > The same thing everyone calls device emulation. In case of virtio-net it
    > > > is in hw/virtio-net.c. If vhost-net is in use device emulation is split
    > > > between userspace and kernel, but it is still just device emulation.
    > >
    > >
    > > case in point, virtio net does not know about pci at all,
    > > so it can not deassert.
    > >
    > I don't see what PCI has to do with it. virtio-net device implementation is
    > split between several files. virtio-net/virtio-ring/virtio-pci. All of
    > them still implement one emulated device. Whoever implemented virtio-net
    > initially decided to put irq ack register into PCI config space, so code
    > that does de-assert is in virtio-pci,
    > but it is still part of emulated
    > device.
    >
    > > > > qemu has code to de-assert. vhost has code to assert.
    > > > Good. So qemu will de-assert. So what do you mean by
    > > > "KVM would need to find all irqfd objects mapped to gsi and notify
    > > > them on deassert"
    > > >
    > > > > I would like to optimize level interrupts and stop driving
    > > > > scheduler insane if at all possible.
    > > > >
    > > > Worthy goal. Do it in irqfd. Irqfd shouldn't call kvm_set_irq() if irq
    > > > level hasn't changed.
    > >
    > > Right. Then it needs to know about deasserts. It does not get this
    > Dessert should be done by qemu writing 0 into irqfd.

    writing 0 to eventfd does nothing. The way to deassert irq
    is currently through ioctl and it seems entirely sensible
    to me to keep it that way.

    Also - which irqfd :)
    We need multiple irqfds to map to a single gsi, with kvm
    doing OR on them.

    > Assertion and
    > de-assertion should be done through irqfd.
    > > information, so when kvm gets deassert ioctl it should
    > > locate irqfd object and set level to 0.
    > > See?
    > No.
    >
    > --
    > Gleb.


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