On Mon, 09/22 21:23, Zhang Haoyu wrote: > > > >Amit, > > > >It's related to the big number of ioeventfds used in virtio-serial-pci. With > >virtio-serial-pci's ioeventfd=off, the performance is not affected no matter > >if > >guest initializes it or not. > > > >In my test, there are 12 fds to poll in qemu_poll_ns before loading guest > >virtio_console.ko, whereas 76 once modprobe virtio_console. > > > >Looks like the ppoll takes more time to poll more fds. > > > >Some trace data with systemtap: > > > >12 fds: > > > >time rel_time symbol > >15 (+1) qemu_poll_ns [enter] > >18 (+3) qemu_poll_ns [return] > > > >76 fd: > > > >12 (+2) qemu_poll_ns [enter] > >18 (+6) qemu_poll_ns [return] > > > >I haven't looked at virtio-serial code, I'm not sure if we should reduce the > >number of ioeventfds in virtio-serial-pci or focus on lower level efficiency. > > > Does ioeventfd=off hamper the performance of virtio-serial?
In theory it has an impact, but I have no data about this. If you have a performance demand, it's best to try it against your use case to answer this question. Fam -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
