[V3,6/6] vhost_net: correctly limit the max pending buffers

Submitted by Jason Wang on Sept. 2, 2013, 8:41 a.m.

Details

Message ID 1378111261-14826-7-git-send-email-jasowang@redhat.com
State Accepted
Delegated to: David Miller
Headers show

Commit Message

Jason Wang Sept. 2, 2013, 8:41 a.m.
As Michael point out, We used to limit the max pending DMAs to get better cache
utilization. But it was not done correctly since it was one done when there's no
new buffers submitted from guest. Guest can easily exceeds the limitation by
keeping sending packets.

So this patch moves the check into main loop. Tests shows about 5%-10%
improvement on per cpu throughput for guest tx.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/net.c |   18 +++++++-----------
 1 files changed, 7 insertions(+), 11 deletions(-)

Patch hide | download patch | download mbox

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 8e9dc55..831eb4f 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -363,6 +363,13 @@  static void handle_tx(struct vhost_net *net)
 		if (zcopy)
 			vhost_zerocopy_signal_used(net, vq);
 
+		/* If more outstanding DMAs, queue the work.
+		 * Handle upend_idx wrap around
+		 */
+		if (unlikely((nvq->upend_idx + vq->num - VHOST_MAX_PEND)
+			      % UIO_MAXIOV == nvq->done_idx))
+			break;
+
 		head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
 					 ARRAY_SIZE(vq->iov),
 					 &out, &in,
@@ -372,17 +379,6 @@  static void handle_tx(struct vhost_net *net)
 			break;
 		/* Nothing new?  Wait for eventfd to tell us they refilled. */
 		if (head == vq->num) {
-			int num_pends;
-
-			/* If more outstanding DMAs, queue the work.
-			 * Handle upend_idx wrap around
-			 */
-			num_pends = likely(nvq->upend_idx >= nvq->done_idx) ?
-				    (nvq->upend_idx - nvq->done_idx) :
-				    (nvq->upend_idx + UIO_MAXIOV -
-				     nvq->done_idx);
-			if (unlikely(num_pends > VHOST_MAX_PEND))
-				break;
 			if (unlikely(vhost_enable_notify(&net->dev, vq))) {
 				vhost_disable_notify(&net->dev, vq);
 				continue;