Hi, In case of direct io, without the interrupt remapping in IOMMU (intel VT-d or AMD IOMMU), hypervisor needs to inject interrupt for guest when the guest is scheduled to specific CPU. At the beginning I thought with IOMMU's interrupt remapping, the hardware can directly forward the interrupt to guest without trapping into hypervisor when the interrupt happens, but after reading the Intel VT-d's manual, I found the interrupt mapping feature just add another mapping which allows software to control (mainly) the destination and vector, and we still need hypervisor to inject the interrupt when the guest is scheduled as only after the guest is scheduled, the target CPU can be known. If my understanding is correct, seems the interrupt remapping does not bring any performance improvement. So what's the benefit of IOMMU's interrupt remapping? Can someone explain the usage model of interrupt remapping in IOMMU?
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