[PATCH v4 2/5] vsock/virtio: reduce credit update messages

[Stefano Garzarella]

In order to reduce the number of credit update messages,
we send them only when the space available seen by the
transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE.

Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
---
 include/linux/virtio_vsock.h            |  1 +
 net/vmw_vsock/virtio_transport_common.c | 16 +++++++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index 7d973903f52e..49fc9d20bc43 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -41,6 +41,7 @@ struct virtio_vsock_sock {
 
 	/* Protected by rx_lock */
 	u32 fwd_cnt;
+	u32 last_fwd_cnt;
 	u32 rx_bytes;
 	struct list_head rx_queue;
 };
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 095221f94786..a85559d4d974 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -211,6 +211,7 @@ static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
 void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt)
 {
 	spin_lock_bh(&vvs->tx_lock);
+	vvs->last_fwd_cnt = vvs->fwd_cnt;
 	pkt->hdr.fwd_cnt = cpu_to_le32(vvs->fwd_cnt);
 	pkt->hdr.buf_alloc = cpu_to_le32(vvs->buf_alloc);
 	spin_unlock_bh(&vvs->tx_lock);
@@ -261,6 +262,7 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	struct virtio_vsock_sock *vvs = vsk->trans;
 	struct virtio_vsock_pkt *pkt;
 	size_t bytes, total = 0;
+	u32 free_space;
 	int err = -EFAULT;
 
 	spin_lock_bh(&vvs->rx_lock);
@@ -291,11 +293,19 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 			virtio_transport_free_pkt(pkt);
 		}
 	}
+
+	free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);
+
 	spin_unlock_bh(&vvs->rx_lock);
 
-	/* Send a credit pkt to peer */
-	virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_STREAM,
-					    NULL);
+	/* We send a credit update only when the space available seen
+	 * by the transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE
+	 */
+	if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) {
+		virtio_transport_send_credit_update(vsk,
+						    VIRTIO_VSOCK_TYPE_STREAM,
+						    NULL);
+	}
 
 	return total;
 
-- 
2.20.1