vhost_net: determine whether or not to use zerocopy at one time

Currently, even if the packet length is smaller than VHOST_GOODCOPY_LEN, if
upend_idx != done_idx we still set zcopy_used to true and rollback this choice
later. This could be avoided by determining zerocopy once by checking all
conditions at one time before.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 27 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 8a6dd0d5667c..3f89dea297a3 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -404,43 +404,36 @@ static void handle_tx(struct vhost_net *net)
                                iov_length(nvq->hdr, s), hdr_size);
                         break;
                 }
-                zcopy_used = zcopy && (len >= VHOST_GOODCOPY_LEN ||
-                                       nvq->upend_idx != nvq->done_idx);
+
+                zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
+                                   && (nvq->upend_idx + 1) % UIO_MAXIOV !=
+                                      nvq->done_idx
+                                   && vhost_net_tx_select_zcopy(net);
 
                 /* use msg_control to pass vhost zerocopy ubuf info to skb */
                 if (zcopy_used) {
+                        struct ubuf_info *ubuf;
+                        ubuf = nvq->ubuf_info + nvq->upend_idx;
+
                         vq->heads[nvq->upend_idx].id = head;
-                        if (!vhost_net_tx_select_zcopy(net) ||
-                            len < VHOST_GOODCOPY_LEN) {
-                                /* copy don't need to wait for DMA done */
-                                vq->heads[nvq->upend_idx].len =
-                                                        VHOST_DMA_DONE_LEN;
-                                msg.msg_control = NULL;
-                                msg.msg_controllen = 0;
-                                ubufs = NULL;
-                        } else {
-                                struct ubuf_info *ubuf;
-                                ubuf = nvq->ubuf_info + nvq->upend_idx;
-
-                                vq->heads[nvq->upend_idx].len =
-                                        VHOST_DMA_IN_PROGRESS;
-                                ubuf->callback = vhost_zerocopy_callback;
-                                ubuf->ctx = nvq->ubufs;
-                                ubuf->desc = nvq->upend_idx;
-                                msg.msg_control = ubuf;
-                                msg.msg_controllen = sizeof(ubuf);
-                                ubufs = nvq->ubufs;
-                                kref_get(&ubufs->kref);
-                        }
+                        vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
+                        ubuf->callback = vhost_zerocopy_callback;
+                        ubuf->ctx = nvq->ubufs;
+                        ubuf->desc = nvq->upend_idx;
+                        msg.msg_control = ubuf;
+                        msg.msg_controllen = sizeof(ubuf);
+                        ubufs = nvq->ubufs;
+                        kref_get(&ubufs->kref);
                         nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV;
-                } else
+                } else {
                         msg.msg_control = NULL;
+                        ubufs = NULL;
+                }
                 /* TODO: Check specific error and bomb out unless ENOBUFS? */
                 err = sock->ops->sendmsg(NULL, sock, &msg, len);
                 if (unlikely(err < 0)) {
                         if (zcopy_used) {
-                                if (ubufs)
-                                        vhost_net_ubuf_put(ubufs);
+                                vhost_net_ubuf_put(ubufs);
                                 nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
                                         % UIO_MAXIOV;
                         }