On Thu, Jul 16, 2020 at 09:39:17AM +0800, Zhu, Lingshan wrote:

On 7/15/2020 9:43 PM, Jason Wang wrote:


    On 2020/7/12 下午10:52, Zhu Lingshan wrote:

        Hi All,

        This series intends to implement IRQ offloading for
        vhost_vdpa.

        By the feat of irq forwarding facilities like posted
        interrupt on X86, irq bypass can  help deliver
        interrupts to vCPU directly.

        vDPA devices have dedicated hardware backends like VFIO
        pass-throughed devices. So it would be possible to setup
        irq offloading(irq bypass) for vDPA devices and gain
        performance improvements.

        In my testing, with this feature, we can save 0.1ms
        in a ping between two VFs on average.



    Hi Lingshan:

    During the virtio-networking meeting, Michael spots two possible issues:

    1) do we need an new uAPI to stop the irq offloading?
    2) can interrupt lost during the eventfd ctx?

    For 1) I think we probably not, we can allocate an independent eventfd
    which does not map to MSIX. So the consumer can't match the producer and we
    fallback to eventfd based irq.

Hi Jason,

I wonder why we need to stop irq offloading, but if we need to do so, maybe a new uAPI would be more intuitive to me,
but why and who(user? qemu?) shall initialize this process, based on what kinda of basis to make the decision?

    For 2) it looks to me guest should deal with the irq synchronization when
    mask or unmask MSIX vectors.

Agreed!

Well we need to make sure during a switch each interrupt is reported
*somewhere*: either irq or eventfd - and not lost.

Thanks,
BR
Zhu Lingshan


    What's your thought?

    Thanks





        Zhu Lingshan (7):
           vhost: introduce vhost_call_ctx
           kvm/vfio: detect assigned device via irqbypass manager
           vhost_vdpa: implement IRQ offloading functions in vhost_vdpa
           vDPA: implement IRQ offloading helpers in vDPA core
           virtio_vdpa: init IRQ offloading function pointers to NULL.
           ifcvf: replace irq_request/free with helpers in vDPA core.
           irqbypass: do not start consumer or producer when failed to connect

          arch/x86/kvm/x86.c              | 10 ++++--
          drivers/vdpa/ifcvf/ifcvf_main.c | 11 +++---
          drivers/vdpa/vdpa.c             | 46 +++++++++++++++++++++++++
          drivers/vhost/Kconfig           |  1 +
          drivers/vhost/vdpa.c            | 75
        +++++++++++++++++++++++++++++++++++++++--
          drivers/vhost/vhost.c           | 22 ++++++++----
          drivers/vhost/vhost.h           |  9 ++++-
          drivers/virtio/virtio_vdpa.c    |  2 ++
          include/linux/vdpa.h            | 11 ++++++
          virt/kvm/vfio.c                 |  2 --
          virt/lib/irqbypass.c            | 16 +++++----
          11 files changed, 181 insertions(+), 24 deletions(-)