>>>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. >>> >> I'm not sure, it perhaps depend on which IO mode you chose, qemu pthreads IO, or linux AIO? >> Somebody else do a favour, please. > >That would be definitely good to know:) I didnt know about the modes >as such. Can you clarify? Are you talking about vhost-LIO vs Qemu? The >LIO part, I do believe, is zero copy.. >I have seen pretty high memory usage on QEMU thread, not sure why. > Sorry for my poor knowledge about block subsystem. I don't know about vhost-LIO, do you mean vhost-blk or vhost-scsi? Linux AIO what I said above is the linux native aio, which only works for uncached access(O_DIRECT), qemu main-thread use it to do block IO, qemu pthreads IO means that qemu creates dedicated threads to do block IO job. -- 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
