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    SubjectRe: [External Email] Re: [PATCH v1 0/2] virtio-mmio: support multiple interrupt vectors
    On Mon, Jul 22, 2019 at 4:39 PM Michael S. Tsirkin <mst@redhat.com> wrote:
    >
    > On Mon, Jul 22, 2019 at 11:22:02AM +0800, 李菲 wrote:
    > > On Fri, Jul 19, 2019 at 11:14 PM Michael S. Tsirkin <mst@redhat.com> wrote:
    > > >
    > > > On Fri, Jul 19, 2019 at 09:31:33PM +0800, Fei Li wrote:
    > > > > Hi,
    > > > >
    > > > > This patch series implements multiple interrupt vectors support for
    > > > > virtio-mmio device. This is especially useful for multiqueue vhost-net
    > > > > device when using firecracker micro-vms as the guest.
    > > > >
    > > > > Test result:
    > > > > With 8 vcpus & 8 net queues set, one vhost-net device with 8 irqs can
    > > > > receive 9 times more pps comparing with only one irq:
    > > > > - 564830.38 rxpck/s for 8 irqs on
    > > > > - 67665.06 rxpck/s for 1 irq on
    > > > >
    > > > > Please help to review, thanks!
    > > > >
    > > > > Have a nice day
    > > > > Fei
    > > >
    > > >
    > > > Interesting. The spec says though:
    > > >
    > > > 4.2.3.4
    > > > Notifications From The Device
    > > > The memory mapped virtio device is using a single, dedicated interrupt signal, which is asserted when at
    > > > least one of the bits described in the description of InterruptStatus is set. This is how the device sends a
    > > > used buffer notification or a configuration change notification to the device.
    > > >
    > > Yes, the spec needs to be updated if we want to use mult-irqs.
    > > >
    > > > So I'm guessing we need to change the host/guest interface?
    > > Just to confirm, does the "the host/guest interface" you mentioned mean how to
    > > pass the irq information from the user space tool to guest kernel?
    > > In this patch, we do this by passing the [irq_start, irq_end]
    > > interface via setting guest
    > > kernel command line, that is done in vm_cmdline_set().
    > > Also there is another way to do this: add two new registers describing irq info
    > > (irq_start & irq_end OR irq_start & irq_numbers) to the virtio config space.
    > >
    > > Which one do you prefer?
    >
    > I'm not sure - so far irq was passed on the command line, right?
    Yes.
    >
    > The first step in implementing any spec change would be to update qemu
    > code to virtio 1. Which is not a huge project but so far no one
    > bothered.
    Emm, actually I only did the test with using firecracker to start a
    micro-vm, but without qemu.
    To be honest, the reason why implementing multi-irq on virtio-mmio is
    mainly because the
    current firecracker using virtio-mmio device and it has no pci thing,
    thus no msi/msix to
    handle the interruptions.
    On the other hand, considering pci is well supported in qemu, I am
    wondering whether we
    still need this. If needed, we would like to do this. :)

    Have a nice day, thanks
    Fei
    >
    >
    > > > If true pls cc virtio-dev.
    > > Sure.
    > > >
    > > > Also, do we need to update dt bindings documentation?
    > > You mean the following doc? Sure. :)
    > > https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/virtio/mmio.txt
    > >
    > > Thanks for the review!
    > >
    > > Have a nice day
    > > Fei
    > >
    > >
    > > >
    > > > >
    > > > > Fam Zheng (1):
    > > > > virtio-mmio: Process vrings more proactively
    > > > >
    > > > > Fei Li (1):
    > > > > virtio-mmio: support multiple interrupt vectors
    > > > >
    > > > > drivers/virtio/virtio_mmio.c | 238 +++++++++++++++++++++++++++++++++++--------
    > > > > 1 file changed, 196 insertions(+), 42 deletions(-)
    > > > >
    > > > > --
    > > > > 2.11.0

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