vhost_net: basic polling support
This patch tries to poll for new added tx buffer or socket receive
queue for a while at the end of tx/rx processing. The maximum time
spent on polling were specified through a new kind of vring ioctl.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 7bd75ff..f744eeb 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -287,6 +287,43 @@
rcu_read_unlock_bh();
}
+static inline unsigned long busy_clock(void)
+{
+ return local_clock() >> 10;
+}
+
+static bool vhost_can_busy_poll(struct vhost_dev *dev,
+ unsigned long endtime)
+{
+ return likely(!need_resched()) &&
+ likely(!time_after(busy_clock(), endtime)) &&
+ likely(!signal_pending(current)) &&
+ !vhost_has_work(dev);
+}
+
+static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
+ struct vhost_virtqueue *vq,
+ struct iovec iov[], unsigned int iov_size,
+ unsigned int *out_num, unsigned int *in_num)
+{
+ unsigned long uninitialized_var(endtime);
+ int r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
+ out_num, in_num, NULL, NULL);
+
+ if (r == vq->num && vq->busyloop_timeout) {
+ preempt_disable();
+ endtime = busy_clock() + vq->busyloop_timeout;
+ while (vhost_can_busy_poll(vq->dev, endtime) &&
+ vhost_vq_avail_empty(vq->dev, vq))
+ cpu_relax_lowlatency();
+ preempt_enable();
+ r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
+ out_num, in_num, NULL, NULL);
+ }
+
+ return r;
+}
+
/* Expects to be always run from workqueue - which acts as
* read-size critical section for our kind of RCU. */
static void handle_tx(struct vhost_net *net)
@@ -331,10 +368,9 @@
% UIO_MAXIOV == nvq->done_idx))
break;
- head = vhost_get_vq_desc(vq, vq->iov,
- ARRAY_SIZE(vq->iov),
- &out, &in,
- NULL, NULL);
+ head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
+ ARRAY_SIZE(vq->iov),
+ &out, &in);
/* On error, stop handling until the next kick. */
if (unlikely(head < 0))
break;
@@ -435,6 +471,38 @@
return len;
}
+static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
+{
+ struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
+ struct vhost_virtqueue *vq = &nvq->vq;
+ unsigned long uninitialized_var(endtime);
+ int len = peek_head_len(sk);
+
+ if (!len && vq->busyloop_timeout) {
+ /* Both tx vq and rx socket were polled here */
+ mutex_lock(&vq->mutex);
+ vhost_disable_notify(&net->dev, vq);
+
+ preempt_disable();
+ endtime = busy_clock() + vq->busyloop_timeout;
+
+ while (vhost_can_busy_poll(&net->dev, endtime) &&
+ skb_queue_empty(&sk->sk_receive_queue) &&
+ vhost_vq_avail_empty(&net->dev, vq))
+ cpu_relax_lowlatency();
+
+ preempt_enable();
+
+ if (vhost_enable_notify(&net->dev, vq))
+ vhost_poll_queue(&vq->poll);
+ mutex_unlock(&vq->mutex);
+
+ len = peek_head_len(sk);
+ }
+
+ return len;
+}
+
/* This is a multi-buffer version of vhost_get_desc, that works if
* vq has read descriptors only.
* @vq - the relevant virtqueue
@@ -553,7 +621,7 @@
vq->log : NULL;
mergeable = vhost_has_feature(vq, VIRTIO_NET_F_MRG_RXBUF);
- while ((sock_len = peek_head_len(sock->sk))) {
+ while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk))) {
sock_len += sock_hlen;
vhost_len = sock_len + vhost_hlen;
headcount = get_rx_bufs(vq, vq->heads, vhost_len,