On 10/19/2015 1:16 PM, Stephen Hemminger wrote:
> 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.
I see you reorganized the code. It is more clear and readable with your
change, but no check is removed.
We could remove the check after virtio_xmit_cleanup. In current
implementation, we assume the virtio_xmit_cleanup and vq_ring_free_chain
always succeed.
> This can help performance and simplifies loop.
>
> Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
> ---
> drivers/net/virtio/virtio_rxtx.c | 66
> ++++++++++++++++------------------------
> 1 file changed, 27 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/net/virtio/virtio_rxtx.c
> b/drivers/net/virtio/virtio_rxtx.c
> index c5b53bb..5b50ed0 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -745,7 +745,6 @@ 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;
>
> @@ -759,57 +758,46 @@ 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;
> + for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
> + struct rte_mbuf *txm = tx_pkts[nb_tx];
> + int need = txm->nb_segs - txvq->vq_free_cnt + 1;
>
> - while (nb_tx < nb_pkts) {
> - /* Need one more descriptor for virtio header. */
> - int need = tx_pkts[nb_tx]->nb_segs - txvq->vq_free_cnt + 1;
> -
> - /*Positive value indicates it need free vring descriptors */
> + /* Positive value indicates it need free vring descriptors */
As you fix the comment, if it is correct, could you do s/need/needs/ as
well, :)?
> 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;
> - }
Still need is rechecked here. It could be removed if virtio_xmit_cleanup
ensures need would be <= 0 after the call.
> + 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;
> - } 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;
> }
>
> txvq->packets += nb_tx;
