[Question] Reduce the msix_load cost for VFIO device

[Longpeng (Mike, Cloud Infrastructure Service Product Dept.)]

Hi Alex,

We found that the msix_load() will cost 40~50ms if the VF has 60+ interrupts,
the following code cost too much for each interrupt:

msix_load:
  for (vector = 0; vector < 60; vector++)
    msix_handle_mask_update
      vfio_msix_vector_do_use
        vfio_add_kvm_msi_virq
          kvm_irqchip_add_msi_route
            kvm_irqchip_commit_routes <-- cost 0.8ms each time

In irq remapping mode, the VF interrupts are not routed through KVM irqchip
in fact, so maybe we can reduce this cost by "x-no-kvm-msix=ture", right?
Are there any risks if we do in this way ?

Looking forward to your reply, thanks.