[PATCH v3 3/5] 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 <sgarz...@redhat.com>
---
 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 53703fe03681..23396b996214 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 buf_alloc;
        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 694d9805f989..f7b0c4911308 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -212,6 +212,7 @@ 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->rx_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->rx_lock);
@@ -262,6 +263,7 @@ 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);
@@ -292,11 +294,19 @@ 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