Re: [RFC v2 3/7] vsock: batch buffers in tx

Vsock uses buffers in order, and for tx driver doesn't have to
know the length of the buffer. So we can do a batch for vsock if
in order negotiated, only write one used ring for a batch of buffers

Signed-off-by: Guo Zhi <redacted>
---
 drivers/vhost/vsock.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 368330417bde..b0108009c39a 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c

@@ -500,6 +500,7 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
        int head, pkts = 0, total_len = 0;
        unsigned int out, in;
        bool added = false;
+       int last_head = -1;

        mutex_lock(&vq->mutex);

@@ -551,10 +552,16 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
                else
                        virtio_transport_free_pkt(pkt);

-               vhost_add_used(vq, head, 0);
+               if (!vhost_has_feature(vq, VIRTIO_F_IN_ORDER))
+                       vhost_add_used(vq, head, 0);
+               else
+                       last_head = head;
                added = true;
        } while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));

+       /* If in order feature negotiaged, we can do a batch to increase performance */
+       if (vhost_has_feature(vq, VIRTIO_F_IN_ORDER) && last_head != -1)
+               vhost_add_used(vq, last_head, 0);