vhost_net: use vhost_add_used_and_signal_n() in vhost_zerocopy_signal…

…_used() We tend to batch the used adding and signaling in vhost_zerocopy_callback() which may result more than 100 used buffers to be updated in vhost_zerocopy_signal_used() in some cases. So switch to use vhost_add_used_and_signal_n() to avoid multiple calls to vhost_add_used_and_signal(). Which means much less times of used index updating and memory barriers. 2% performance improvement were seen on netperf TCP_RR test. Signed-off-by: Jason Wang <[email protected]> Signed-off-by: David S. Miller <[email protected]>
kishon · Sep 4, 2013 · c92112a · c92112a
1 parent 094afe7
commit c92112a
Showing 1 changed file with 8 additions and 5 deletions.
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
@@ -281,22 +281,25 @@ static void vhost_zerocopy_signal_used(struct vhost_net *net,
 {
 	struct vhost_net_virtqueue *nvq =
 		container_of(vq, struct vhost_net_virtqueue, vq);
-	int i;
+	int i, add;
 	int j = 0;
 
 	for (i = nvq->done_idx; i != nvq->upend_idx; i = (i + 1) % UIO_MAXIOV) {
 		if (vq->heads[i].len == VHOST_DMA_FAILED_LEN)
 			vhost_net_tx_err(net);
 		if (VHOST_DMA_IS_DONE(vq->heads[i].len)) {
 			vq->heads[i].len = VHOST_DMA_CLEAR_LEN;
-			vhost_add_used_and_signal(vq->dev, vq,
-						  vq->heads[i].id, 0);
 			++j;
 		} else
 			break;
 	}
-	if (j)
-		nvq->done_idx = i;
+	while (j) {
+		add = min(UIO_MAXIOV - nvq->done_idx, j);
+		vhost_add_used_and_signal_n(vq->dev, vq,
+					    &vq->heads[nvq->done_idx], add);
+		nvq->done_idx = (nvq->done_idx + add) % UIO_MAXIOV;
+		j -= add;
+	}
 }
 
 static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)