On Mon, Jan 24, 2011 at 07:54:20PM +0100, Kevin Wolf wrote: > 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
Does it help if you set ioeventfd=off on command line?
