Re: [Qemu-devel] [RFC PATCH 0/4] MSI affinity for assigned devices

[Krishna J]

Hi Alex,

> MSI routing updates aren't currently handled by pci-assign or
> vfio-pci (when using KVM acceleration), which means that trying to
> set interrupt SMP affinity in the guest has no effect unless MSI is
> completely disabled and re-enabled. This series fixes this for both
> device assignment backends using similar schemes. We store the last
> MSIMessage programmed to KVM and do updates to the MSI route when it
> changes. pci-assign takes a little bit of refactoring to make this
> happen cleanly. Thanks,

I am using the MSI affinity for assigned devices patch 1 to 4. I have setup the guest such that VCPU0 is pinned to PCPU1, VCPU1 is pinned to PCPU2, VCPU2 is pinned to PCPU3 and VCPU3 is pinned to PCPU4. I do this by taskset after the guest boots. I then start generating interrupts affined to VCPU3. I see all the interrupts directly delivered to VCPU 3. Now i do the same test but interrupt affined to VCPU 2. Although the interrupts are delivered to VCPU2  there are lot of "Rescheduling interrupts" in VCPU 3. I have checked the smp_affinity and it is updated to VCPU 2. 

Wanted to know your feedback on this usecase and what might be the impact. 

           CPU0       CPU1 CPU2       CPU3

  0:        211          0          0          0   IO-APIC-edge      timer

  4:  60940          0          0          0   IO-APIC-edge      serial

  8:         65          0          0          0   IO-APIC-edge      rtc0

  9:          0          0          0          0   IO-APIC-fasteoi   acpi

 40:          0          0          0          0   PCI-MSI-edge      virtio1-config

 41:   1910          0          0          0   PCI-MSI-edge      virtio1-requests

 42:          0          0          0          0   PCI-MSI-edge      virtio0-config

 43:        127          0          0          0   PCI-MSI-edge      virtio0-input

 44:          1          0          0          0   PCI-MSI-edge      virtio0-output

 45:          1          0       3377      11194   PCI-MSI-edge      FPGA_DEV

NMI:          0          0          0          0   Non-maskable interrupts

LOC:     225880     231572     223670     223612   Local timer interrupts

SPU:          0          0          0          0   Spurious interrupts

PMI:          0          0          0          0   Performance monitoring interrupts

IWI:          0          0          0          0   IRQ work interrupts

RTR:          0          0          0          0   APIC ICR read retries

RES:         14         20         21       3398   Rescheduling interrupts-------> Many RES Interrtups!!!!!!

CAL:          0         14         14         16   Function call interrupts

TLB:          0          0          0          0   TLB shootdowns

thanks,

Krishna