On 2020/7/16 上午9:39, Zhu, Lingshan wrote:

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

quoted

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

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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?

The reason is we may want to fallback to software datapath for some 
reason (e.g software assisted live migration). In this case we need 
intercept device write to used ring so we can not offloading virtqueue 
interrupt in this case.

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

Agreed!

It's better to double check for this.

Thanks

Thanks,
BR
Zhu Lingshan

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What's your thought?

Thanks

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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(-)