On 10/19/2015 11:48 PM, Stephen Hemminger wrote:
> 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.
Is there the case in current implementation virtio_xmit_cleanup could
free up any descriptors, i.e, dxp->ndesc is zero?
vq->free_cnt += dxp->ndesc
>
>>> 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;
>
