virtio: clean up Tx space checks

The space check for transmit ring only needs a single conditional.
I.e only need to recheck for space if there was no space in first check.

This can help performance and simplifies loop.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>

diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
index 466fee6..74b39ef 100644 (file)
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -832,7 +832,6 @@ uint16_t
 virtio_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 {
        struct virtqueue *txvq = tx_queue;
-       struct rte_mbuf *txm;
        uint16_t nb_used, nb_tx;
        int error;
 
@@ -846,58 +845,49 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
        if (likely(nb_used > txvq->vq_nentries - txvq->vq_free_thresh))
                virtio_xmit_cleanup(txvq, nb_used);
 
-       nb_tx = 0;
-
-       while (nb_tx < nb_pkts) {
+       for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
+               struct rte_mbuf *txm = tx_pkts[nb_tx];
                /* Need one more descriptor for virtio header. */
-               int need = tx_pkts[nb_tx]->nb_segs - txvq->vq_free_cnt + 1;
+               int need = txm->nb_segs - txvq->vq_free_cnt + 1;
 
-               /*Positive value indicates it need free vring descriptors */
+               /* Positive value indicates it need free vring descriptors */
                if (unlikely(need > 0)) {
                        nb_used = VIRTQUEUE_NUSED(txvq);
                        virtio_rmb();
                        need = RTE_MIN(need, (int)nb_used);
 
                        virtio_xmit_cleanup(txvq, need);
-                       need = (int)tx_pkts[nb_tx]->nb_segs -
-                               txvq->vq_free_cnt + 1;
-               }
-
-               /*
-                * Zero or negative value indicates it has enough free
-                * descriptors to use for transmitting.
-                */
-               if (likely(need <= 0)) {
-                       txm = tx_pkts[nb_tx];
-
-                       /* Do VLAN tag insertion */
-                       if (unlikely(txm->ol_flags & PKT_TX_VLAN_PKT)) {
-                               error = rte_vlan_insert(&txm);
-                               if (unlikely(error)) {
-                                       rte_pktmbuf_free(txm);
-                                       ++nb_tx;
-                                       continue;
-                               }
+                       need = txm->nb_segs - txvq->vq_free_cnt + 1;
+                       if (unlikely(need > 0)) {
+                               PMD_TX_LOG(ERR,
+                                          "No free tx descriptors to transmit");
+                               break;
                        }
+               }
 
-                       /* Enqueue Packet buffers */
-                       error = virtqueue_enqueue_xmit(txvq, txm);
+               /* Do VLAN tag insertion */
+               if (unlikely(txm->ol_flags & PKT_TX_VLAN_PKT)) {
+                       error = rte_vlan_insert(&txm);
                        if (unlikely(error)) {
-                               if (error == ENOSPC)
-                                       PMD_TX_LOG(ERR, "virtqueue_enqueue Free count = 0");
-                               else if (error == EMSGSIZE)
-                                       PMD_TX_LOG(ERR, "virtqueue_enqueue Free count < 1");
-                               else
-                                       PMD_TX_LOG(ERR, "virtqueue_enqueue error: %d", error);
-                               break;
+                               rte_pktmbuf_free(txm);
+                               continue;
                        }
-                       nb_tx++;
-                       txvq->bytes += txm->pkt_len;
-                       virtio_update_packet_stats(txvq, txm);
-               } else {
-                       PMD_TX_LOG(ERR, "No free tx descriptors to transmit");
+               }
+
+               /* Enqueue Packet buffers */
+               error = virtqueue_enqueue_xmit(txvq, txm);
+               if (unlikely(error)) {
+                       if (error == ENOSPC)
+                               PMD_TX_LOG(ERR, "virtqueue_enqueue Free count = 0");
+                       else if (error == EMSGSIZE)
+                               PMD_TX_LOG(ERR, "virtqueue_enqueue Free count < 1");
+                       else
+                               PMD_TX_LOG(ERR, "virtqueue_enqueue error: %d", error);
                        break;
                }
+
+               txvq->bytes += txm->pkt_len;
+               virtio_update_packet_stats(txvq, txm);
        }
 
        txvq->packets += nb_tx;