On Mon, 19 Oct 2015 08:02:07 +0000
"Xie, Huawei" <huawei.xie at intel.com> wrote:
> 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.
The only case that matters is if virtio_xmit_cleanup can not
free up any slots.
> > 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;
>
