Re: [PATCH v2 net-next 3/4] vhost_net: Avoid rx queue wake-ups during busypoll

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On 2018年07月03日 15:31, Toshiaki Makita wrote:
We may run handle_rx() while rx work is queued. For example a packet can
push the rx work during the window before handle_rx calls
vhost_net_disable_vq().
In that case busypoll immediately exits due to vhost_has_work()
condition and enables vq again. This can lead to another unnecessary rx
wake-ups, so poll rx work instead of enabling the vq.

Signed-off-by: Toshiaki Makita <makita.toshiaki@xxxxxxxxxxxxx>
---
  drivers/vhost/net.c | 26 +++++++++++++++++++-------
  1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 811c0e5..791bc8b 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -653,7 +653,8 @@ static void vhost_rx_signal_used(struct vhost_net_virtqueue *nvq)
  	nvq->done_idx = 0;
  }
-static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
+static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
+				      bool *busyloop_intr)
  {
  	struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
  	struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
@@ -671,11 +672,16 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
  		preempt_disable();
  		endtime = busy_clock() + tvq->busyloop_timeout;
- while (vhost_can_busy_poll(endtime) &&
-		       !vhost_has_work(&net->dev) &&
-		       !sk_has_rx_data(sk) &&
-		       vhost_vq_avail_empty(&net->dev, tvq))
+		while (vhost_can_busy_poll(endtime)) {
+			if (vhost_has_work(&net->dev)) {
+				*busyloop_intr = true;
+				break;
+			}
+			if (sk_has_rx_data(sk) ||
+			    !vhost_vq_avail_empty(&net->dev, tvq))
+				break;
  			cpu_relax();
+		}
preempt_enable(); @@ -795,6 +801,7 @@ static void handle_rx(struct vhost_net *net)
  	s16 headcount;
  	size_t vhost_hlen, sock_hlen;
  	size_t vhost_len, sock_len;
+	bool busyloop_intr = false;
  	struct socket *sock;
  	struct iov_iter fixup;
  	__virtio16 num_buffers;
@@ -818,7 +825,9 @@ static void handle_rx(struct vhost_net *net)
  		vq->log : NULL;
  	mergeable = vhost_has_feature(vq, VIRTIO_NET_F_MRG_RXBUF);
- while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk))) {
+	while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk,
+						      &busyloop_intr))) {
+		busyloop_intr = false;
  		sock_len += sock_hlen;
  		vhost_len = sock_len + vhost_hlen;
  		headcount = get_rx_bufs(vq, vq->heads + nvq->done_idx,
@@ -905,7 +914,10 @@ static void handle_rx(struct vhost_net *net)
  			goto out;
  		}
  	}
-	vhost_net_enable_vq(net, vq);
+	if (unlikely(busyloop_intr))
+		vhost_poll_queue(&vq->poll);
+	else
+		vhost_net_enable_vq(net, vq);
  out:
  	vhost_rx_signal_used(nvq);
  	mutex_unlock(&vq->mutex);

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>




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