Am 12.12.2010 16:02, schrieb Stefan Hajnoczi: > Virtqueue notify is currently handled synchronously in userspace virtio. This > prevents the vcpu from executing guest code while hardware emulation code > handles the notify. > > On systems that support KVM, the ioeventfd mechanism can be used to make > virtqueue notify a lightweight exit by deferring hardware emulation to the > iothread and allowing the VM to continue execution. This model is similar to > how vhost receives virtqueue notifies. > > The result of this change is improved performance for userspace virtio > devices. > Virtio-blk throughput increases especially for multithreaded scenarios and > virtio-net transmit throughput increases substantially. > > Some virtio devices are known to have guest drivers which expect a notify to > be > processed synchronously and spin waiting for completion. Only enable > ioeventfd > for virtio-blk and virtio-net for now. > > Care must be taken not to interfere with vhost-net, which uses host > notifiers. If the set_host_notifier() API is used by a device > virtio-pci will disable virtio-ioeventfd and let the device deal with > host notifiers as it wishes. > > After migration and on VM change state (running/paused) virtio-ioeventfd > will enable/disable itself. > > * VIRTIO_CONFIG_S_DRIVER_OK -> enable virtio-ioeventfd > * !VIRTIO_CONFIG_S_DRIVER_OK -> disable virtio-ioeventfd > * virtio_pci_set_host_notifier() -> disable virtio-ioeventfd > * vm_change_state(running=0) -> disable virtio-ioeventfd > * vm_change_state(running=1) -> enable virtio-ioeventfd > > Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
On current git master I'm getting hangs when running iozone on a virtio-blk disk. "Hang" means that it's not responsive any more and has 100% CPU consumption. I bisected the problem to this patch. Any ideas? Kevin
