On Thu, Sep 30, 2010 at 03:01:52PM +0100, Stefan Hajnoczi wrote: > 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. > Full numbers are below. > > This patch employs ioeventfd virtqueue notify for all virtio devices. > Linux kernels pre-2.6.34 only allow for 6 ioeventfds per VM and care > must be taken so that vhost-net, the other ioeventfd user in QEMU, is > able to function. On such kernels ioeventfd virtqueue notify will not > be used. > > Khoa Huynh <khoa@xxxxxxxxxx> collected the following data for > virtio-blk with cache=none,aio=native: > > FFSB Test Threads Unmodified Patched > (MB/s) (MB/s) > Large file create 1 21.7 21.8 > 8 101.0 118.0 > 16 119.0 157.0 > > Sequential reads 1 21.9 23.2 > 8 114.0 139.0 > 16 143.0 178.0 > > Random reads 1 3.3 3.6 > 8 23.0 25.4 > 16 43.3 47.8 > > Random writes 1 22.2 23.0 > 8 93.1 111.6 > 16 110.5 132.0 > > Sridhar Samudrala <sri@xxxxxxxxxx> collected the following data for > virtio-net with 2.6.36-rc1 on the host and 2.6.34 on the guest. > > Guest to Host TCP_STREAM throughput(Mb/sec) > ------------------------------------------- > Msg Size vhost-net virtio-net virtio-net/ioeventfd > 65536 12755 6430 7590 > 16384 8499 3084 5764 > 4096 4723 1578 3659 > 1024 1827 981 2060 > > Host to Guest TCP_STREAM throughput(Mb/sec) > ------------------------------------------- > Msg Size vhost-net virtio-net virtio-net/ioeventfd > 65536 11156 5790 5853 > 16384 10787 5575 5691 > 4096 10452 5556 4277 > 1024 4437 3671 5277 > > Guest to Host TCP_RR latency(transactions/sec) > ---------------------------------------------- > > Msg Size vhost-net virtio-net virtio-net/ioeventfd > 1 9903 3459 3425 > 4096 7185 1931 1899 > 16384 6108 2102 1923 > 65536 3161 1610 1744 > > Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxxxxxxxxxx> > --- > Small changes are required for qemu-kvm.git. I will send them once qemu.git > has virtio-ioeventfd support. > > hw/vhost.c | 6 ++-- > hw/virtio.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > hw/virtio.h | 9 +---- > kvm-all.c | 39 +++++++++++++++++++++ > kvm-stub.c | 5 +++ > kvm.h | 1 + > 6 files changed, 156 insertions(+), 10 deletions(-) Is there anything stopping this patch from being merged? Thanks, Stefan -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
