[PATCH net-next 8/8] vhost-net: reduce vq polling on tx zerocopy

Michael S. Tsirkin
2012-10-29T15:47:43Z

It seems that to avoid deadlocks it is enough to poll vq before
we are going to use the last buffer. This should be faster than
c70aa540c7a9f67add11ad3161096fb95233aa2e.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/net.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 8e9de79..3967f82 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -197,8 +197,16 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, int status)
{
struct vhost_ubuf_ref *ubufs = ubuf->ctx;
struct vhost_virtqueue *vq = ubufs->vq;
-
- vhost_poll_queue(&vq->poll);
+ int cnt = atomic_read(&ubufs->kref.refcount);
+
+ /*
+ * Trigger polling thread if guest stopped submitting new buffers:
+ * in this case, the refcount after decrement will eventually reach 1
+ * so here it is 2.
+ * We also trigger polling periodically after each 16 packets.
+ */
+ if (cnt <= 2 || !(cnt % 16))
+ vhost_poll_queue(&vq->poll);
/* set len to mark this desc buffers done DMA */
vq->heads[ubuf->desc].len = status ?
VHOST_DMA_FAILED_LEN : VHOST_DMA_DONE_LEN;
--
MST