On 2020/2/10 下午5:05, Zha Bin wrote:
From: Liu Jiang<ge...@linux.alibaba.com> Userspace VMMs (e.g. Qemu microvm, Firecracker) take advantage of using virtio over mmio devices as a lightweight machine model for modern cloud. The standard virtio over MMIO transport layer only supports one legacy interrupt, which is much heavier than virtio over PCI transport layer using MSI. Legacy interrupt has long work path and causes specific VMExits in following cases, which would considerably slow down the performance: 1) read interrupt status register 2) update interrupt status register 3) write IOAPIC EOI register We proposed to add MSI support for virtio over MMIO via new feature bit VIRTIO_F_MMIO_MSI[1] which increases the interrupt performance. With the VIRTIO_F_MMIO_MSI feature bit supported, the virtio-mmio MSI uses msi_sharing[1] to indicate the event and vector mapping. Bit 1 is 0: device uses non-sharing and fixed vector per event mapping. Bit 1 is 1: device uses sharing mode and dynamic mapping.
I believe dynamic mapping should cover the case of fixed vector? Thanks
