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| author | Stefan Hajnoczi | 2019-12-09 22:09:57 +0100 |
|---|---|---|
| committer | Michael S. Tsirkin | 2020-01-05 13:03:03 +0100 |
| commit | d0435bc513e23a4961b6af20164d1c6c219eb4ea (patch) | |
| tree | 0434e1d07119ee8ea9e80143a5aa0a8c82cff41c /include/hw/virtio | |
| parent | Implement backend program convention command for vhost-user-blk (diff) | |
| download | qemu-d0435bc513e23a4961b6af20164d1c6c219eb4ea.tar.gz qemu-d0435bc513e23a4961b6af20164d1c6c219eb4ea.tar.xz qemu-d0435bc513e23a4961b6af20164d1c6c219eb4ea.zip | |
virtio: don't enable notifications during polling
Virtqueue notifications are not necessary during polling, so we disable
them. This allows the guest driver to avoid MMIO vmexits.
Unfortunately the virtio-blk and virtio-scsi handler functions re-enable
notifications, defeating this optimization.
Fix virtio-blk and virtio-scsi emulation so they leave notifications
disabled. The key thing to remember for correctness is that polling
always checks one last time after ending its loop, therefore it's safe
to lose the race when re-enabling notifications at the end of polling.
There is a measurable performance improvement of 5-10% with the null-co
block driver. Real-life storage configurations will see a smaller
improvement because the MMIO vmexit overhead contributes less to
latency.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20191209210957.65087-1-stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Diffstat (limited to 'include/hw/virtio')
| -rw-r--r-- | include/hw/virtio/virtio.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h index 777772475c..b69d517496 100644 --- a/include/hw/virtio/virtio.h +++ b/include/hw/virtio/virtio.h @@ -228,6 +228,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id); void virtio_notify_config(VirtIODevice *vdev); +bool virtio_queue_get_notification(VirtQueue *vq); void virtio_queue_set_notification(VirtQueue *vq, int enable); int virtio_queue_ready(VirtQueue *vq); |