Re: [PATCH V2 1/2] vhost_net: stop polling socket during rx processing
From: Jason Wang
Date: Mon May 30 2016 - 23:14:40 EST
On 2016å05æ30æ 23:47, Michael S. Tsirkin wrote:
On Mon, May 30, 2016 at 02:47:53AM -0400, Jason Wang wrote:
We don't stop rx polling socket during rx processing, this will lead
unnecessary wakeups from under layer net devices (E.g
sock_def_readable() form tun). Rx will be slowed down in this
way. This patch avoids this by stop polling socket during rx
processing. A small drawback is that this introduces some overheads in
light load case because of the extra start/stop polling, but single
netperf TCP_RR does not notice any change. In a super heavy load case,
e.g using pktgen to inject packet to guest, we get about ~8.8%
improvement on pps:
before: ~1240000 pkt/s
after: ~1350000 pkt/s
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
drivers/vhost/net.c | 56 +++++++++++++++++++++++++++--------------------------
1 file changed, 29 insertions(+), 27 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 10ff494..e91603b 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -301,6 +301,32 @@ static bool vhost_can_busy_poll(struct vhost_dev *dev,
!vhost_has_work(dev);
}
+static void vhost_net_disable_vq(struct vhost_net *n,
+ struct vhost_virtqueue *vq)
+{
+ struct vhost_net_virtqueue *nvq =
+ container_of(vq, struct vhost_net_virtqueue, vq);
+ struct vhost_poll *poll = n->poll + (nvq - n->vqs);
+ if (!vq->private_data)
+ return;
+ vhost_poll_stop(poll);
+}
+
+static int vhost_net_enable_vq(struct vhost_net *n,
+ struct vhost_virtqueue *vq)
+{
+ struct vhost_net_virtqueue *nvq =
+ container_of(vq, struct vhost_net_virtqueue, vq);
+ struct vhost_poll *poll = n->poll + (nvq - n->vqs);
+ struct socket *sock;
+
+ sock = vq->private_data;
+ if (!sock)
+ return 0;
+
+ return vhost_poll_start(poll, sock->file);
+}
+
static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
struct vhost_virtqueue *vq,
struct iovec iov[], unsigned int iov_size,
BTW we might want to rename these functions, name no longer
reflects function ...
Do you mean adding something reflect busy polling in the name? Then the
name may be too long or have suggestion on the name?
@@ -627,6 +653,7 @@ static void handle_rx(struct vhost_net *net)
if (!sock)
goto out;
vhost_disable_notify(&net->dev, vq);
+ vhost_net_disable_vq(net, vq);
vhost_hlen = nvq->vhost_hlen;
sock_hlen = nvq->sock_hlen;
@@ -715,9 +742,10 @@ static void handle_rx(struct vhost_net *net)
total_len += vhost_len;
if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
vhost_poll_queue(&vq->poll);
- break;
+ goto out;
}
}
+ vhost_net_enable_vq(net, vq);
OK so if sock is readable but RX VQ is empty, this will
immediately schedule another round of handle_rx and so ad
infinitum,
Looks like a bug.
Yes it is, will change the above headcount check to:
/* OK, now we need to know about added descriptors. */
if (!headcount) {
if (unlikely(vhost_enable_notify(&net->dev, vq))) {
/* They have slipped one in as we were
* doing that: check again. */
vhost_disable_notify(&net->dev, vq);
continue;
}
/* Nothing new? Wait for eventfd to tell us
* they refilled. */
goto out;
}
out:
mutex_unlock(&vq->mutex);
}
@@ -796,32 +824,6 @@ static int vhost_net_open(struct inode *inode, struct file *f)
return 0;
}
-static void vhost_net_disable_vq(struct vhost_net *n,
- struct vhost_virtqueue *vq)
-{
- struct vhost_net_virtqueue *nvq =
- container_of(vq, struct vhost_net_virtqueue, vq);
- struct vhost_poll *poll = n->poll + (nvq - n->vqs);
- if (!vq->private_data)
- return;
- vhost_poll_stop(poll);
-}
-
-static int vhost_net_enable_vq(struct vhost_net *n,
- struct vhost_virtqueue *vq)
-{
- struct vhost_net_virtqueue *nvq =
- container_of(vq, struct vhost_net_virtqueue, vq);
- struct vhost_poll *poll = n->poll + (nvq - n->vqs);
- struct socket *sock;
-
- sock = vq->private_data;
- if (!sock)
- return 0;
-
- return vhost_poll_start(poll, sock->file);
-}
-
static struct socket *vhost_net_stop_vq(struct vhost_net *n,
struct vhost_virtqueue *vq)
{
--
1.8.3.1
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html