On Tue, Dec 05, 2023 at 09:48:05AM +0300, Arseniy Krasnov wrote:
Add one more condition for sending credit update during dequeue from
stream socket: when number of bytes in the rx queue is smaller than
SO_RCVLOWAT value of the socket. This is actual for non-default value
of SO_RCVLOWAT (e.g. not 1) - idea is to "kick" peer to continue data
transmission, because we need at least SO_RCVLOWAT bytes in our rx
queue to wake up user for reading data (in corner case it is also
possible to stuck both tx and rx sides, this is why 'Fixes' is used).
Fixes: b89d882dc9fc ("vsock/virtio: reduce credit update messages")
Signed-off-by: Arseniy Krasnov <avkrasnov@xxxxxxxxxxxxxxxxx>
---
net/vmw_vsock/virtio_transport_common.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index e137d740804e..461c89882142 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -558,6 +558,7 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
struct virtio_vsock_sock *vvs = vsk->trans;
size_t bytes, total = 0;
struct sk_buff *skb;
+ bool low_rx_bytes;
int err = -EFAULT;
u32 free_space;
@@ -602,6 +603,8 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
}
free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);
+ low_rx_bytes = (vvs->rx_bytes <
+ sock_rcvlowat(sk_vsock(vsk), 0, INT_MAX));
As in the previous patch, should we avoid the update it if `fwd_cnt` and
`last_fwd_cnt` are the same?
Now I'm thinking if it is better to add that check directly in
virtio_transport_send_credit_update().
Stefano
spin_unlock_bh(&vvs->rx_lock);
@@ -611,9 +614,11 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
* too high causes extra messages. Too low causes transmitter
* stalls. As stalls are in theory more expensive than extra
* messages, we set the limit to a high value. TODO: experiment
- * with different values.
+ * with different values. Also send credit update message when
+ * number of bytes in rx queue is not enough to wake up reader.
*/
- if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
+ if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE ||
+ low_rx_bytes)
virtio_transport_send_credit_update(vsk);
return total;
--
2.25.1
