diff mbox

[dpdk-dev,1/5] virtio: clean up space checks on xmit

Message ID 1445231772-17467-2-git-send-email-stephen@networkplumber.org (mailing list archive)
State Changes Requested, archived
Headers

Commit Message

Stephen Hemminger Oct. 19, 2015, 5:16 a.m. UTC 
  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 | 66 ++++++++++++++++------------------------
 1 file changed, 27 insertions(+), 39 deletions(-)

Comments

Huawei Xie Oct. 19, 2015, 8:02 a.m. UTC | #1 
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@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;
Stephen Hemminger Oct. 19, 2015, 3:48 p.m. UTC | #2 
On Mon, 19 Oct 2015 08:02:07 +0000
"Xie, Huawei" <huawei.xie@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@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;
>
Huawei Xie Oct. 19, 2015, 4:27 p.m. UTC | #3 
On 10/19/2015 11:48 PM, Stephen Hemminger wrote:
> On Mon, 19 Oct 2015 08:02:07 +0000
> "Xie, Huawei" <huawei.xie@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@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;
>
diff mbox

Patch

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 */
 		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;
-		} 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;