On Mon, Jan 24, 2011 at 08:48:05PM +0100, Kevin Wolf wrote: > 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
Then it's the ioeventfd that is to blame. Is it the io thread that consumes 100% CPU? Or the vcpu thread? -- MST
