[Xen-devel] interrupt affinity question

["Agarwal, Lomesh" <lomesh.agarwal@xxxxxxxxx>]

From looking at the code it looks like that interrupt affinity will be set for all physical IRQs and it will be set to the physical processor on which VCPU is running which called request_irq.

Can somebody confirm my understanding?

Pirq_guest_bind (in arch/x86/irq.c) calls set_affinity (which will translate to dma_msi_set_affinity function in  arch/x86/hvm/vmx/vtd/intel-iommu.c for VTd).

So that means if request_irq for NIC interrupt is called when a domain with single VCPU is scheduled on physical CPU 1 then NIC interrupt will be bind to physical CPU 1 and later if the same domain is scheduled to physical CPU 0 it won’t get the interrupt until it does a VMEXIT.

So for lower interrupt latency we are should pin domain VCPU also.

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