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>

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 8a6dd0d..3f89dea 100644 (file)
--- 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;
                        }