On Tue, Nov 24 2020 at 21:03, Laurent Vivier wrote:

With virtio multiqueue, normally each queue IRQ is mapped to a CPU.

This problem cannot be shown on x86_64 for two reasons:

There is only _ONE_ reason why this is not a problem on x86. x86 uses
the generic PCI/MSI domain which supports this out of the box.

- the call path traverses arch_setup_msi_irqs() that is arch specific:

   virtscsi_probe()
      virtscsi_init()
         vp_modern_find_vqs()
            vp_find_vqs()
               vp_find_vqs_msix()
                  pci_alloc_irq_vectors_affinity()
                     __pci_enable_msix_range()
                        pci_msi_setup_msi_irqs()
                           arch_setup_msi_irqs()
                              rtas_setup_msi_irqs()

This is a problem on _all_ variants of PPC MSI providers, not only for
pseries. It's not restricted to virtscsi devices either, that's just the
device which made you discover this.

Thanks,

        tglx