[dpdk-dev,2/2] virtio: clean up space checks on xmit
Commit Message
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>
---
drivers/net/virtio/virtio_rxtx.c | 68 +++++++++++++++++-----------------------
1 file changed, 29 insertions(+), 39 deletions(-)
Comments
On Thu, Dec 03, 2015 at 05:12:54PM -0800, 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.
>
> This can help performance and simplifies loop.
This is a good cleanup. Besides that, I have few minor comments below.
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
> drivers/net/virtio/virtio_rxtx.c | 68 +++++++++++++++++-----------------------
> 1 file changed, 29 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> index 466fee6..7cb932a 100644
> --- 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;
While reviewing the code, I found the var name `need' is not properly
taken. Maybe `need_cleanup' is better, and it's better to be defined
as bool type. What do you think of that?
(And yes, it has nothing to do with your patch, I just found it we
can rename it to a better name to improve the code readability a bit.
If you agree, would you submit a patch, or should I do it?)
>
> - /*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;
> + need = txm->nb_segs - txvq->vq_free_cnt + 1;
> + if (unlikely(need > 0)) {
> + PMD_TX_LOG(ERR,
> + "No free tx descriptors to transmit");
> + break;
> + }
^
Minor nit: I found a leading white space there.
Otherwise, it looks good:
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
--yliu
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;
>
> While reviewing the code, I found the var name `need' is not properly
> taken. Maybe `need_cleanup' is better, and it's better to be defined
> as bool type. What do you think of that?
The variable need indicates how many more buffers are needed to
complete the transmit. In later patches, there is a variable slots
so:
needed = slots - free
So if needed is positive, then more buffers are needed than available
and transmit is blocked. If needed is negative then there is free
space available.
>
> (And yes, it has nothing to do with your patch, I just found it we
> can rename it to a better name to improve the code readability a bit.
> If you agree, would you submit a patch, or should I do it?)
>
> >
> > - /*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;
> > + need = txm->nb_segs - txvq->vq_free_cnt + 1;
> > + if (unlikely(need > 0)) {
> > + PMD_TX_LOG(ERR,
> > + "No free tx descriptors to transmit");
> > + break;
> > + }
> ^
>
> Minor nit: I found a leading white space there.
Hmm. I didn't see it in checkpatch.
On Sat, Dec 05, 2015 at 11:50:07AM -0800, Stephen Hemminger wrote:
> 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;
> >
> > While reviewing the code, I found the var name `need' is not properly
> > taken. Maybe `need_cleanup' is better, and it's better to be defined
> > as bool type. What do you think of that?
>
> The variable need indicates how many more buffers are needed to
> complete the transmit. In later patches, there is a variable slots
> so:
> needed = slots - free
>
> So if needed is positive, then more buffers are needed than available
> and transmit is blocked. If needed is negative then there is free
> space available.
Yeah, I knew that. And there is a comment for that (thanks for the
explanation anyway!):
/* Positive value indicates it need free vring descriptors */
I mean, if a var name well taken, we could avoid comments like above.
However, for this case, I simply overlooked that virtio_xmit_cleanup()
takes `need' as the input, so that I thought `need' is just a boolean
var to check if we need to get few more free spaces. And that's how
my above suggestion comes. So, sorry for the noisy.
--yliu
@@ -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;
+ need = txm->nb_segs - txvq->vq_free_cnt + 1;
+ if (unlikely(need > 0)) {
+ PMD_TX_LOG(ERR,
+ "No free tx descriptors to transmit");
+ break;
+ }
}
- /*
- * 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;
- }
- }
-
- /* 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;