Am 24.01.2011 20:47, schrieb Michael S. Tsirkin: > 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?
I was building with the default options, i.e. there is no IO thread. Now I'm just running the test with IO threads enabled, and so far everything looks good. So I can only reproduce the problem with IO threads disabled. Kevin
