>>A few additional questions:) >> >>1. If IO to a block device goes through QEMU and not vhost, are there >>data copies between kernel and user mode if I do IO to a block device >>or is it zero copy? Kind of related to Question (2) also. >> >An additional copy will be avoided only by using vhost, so if you are using vhost you can call it zero copy realtively. I know that kvm support network tx zero-copy when using vhost, but rx copy is still performed in vhost, because the NIC cannot determine DMA to which VM's rx buffers before L2 switching(unless vhost using page-flip between HVA->HPA and GPA->HPA, or macvtap over SRIOV-VF is used). Storage has no this limitation, can vhost-blk and vhost-scsi avoid data copy in both write and read? IIUC, even if vhost is not used, qemu using linux native aio can avoid data copy between user and kernel space, right? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
