Am 24.01.2011 20:36, schrieb Michael S. Tsirkin: > 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?
Yes, with ioeventfd=off it seems to work fine. Kevin
