[PATCH net-next 0/2] mvneta xmit_more and bql support

[PATCH net-next 0/2] mvneta xmit_more and bql support

[Marcin Wojtas]

Hi,

This short patchset introduces two enhancements to mvneta driver
TX packets concatenation support using xmit_more mechanism and also
byte queue limit in order to decrease latency on saturated links.

Any comments or feedback would be welcome.

Best regards,
Marcin

Marcin Wojtas (1):
  net: mvneta: add BQL support

Simon Guinot (1):
  net: mvneta: add xmit_more support

 drivers/net/ethernet/marvell/mvneta.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

-- 
1.8.3.1

[PATCH net-next 1/2] net: mvneta: add xmit_more support

[Marcin Wojtas]

From: Simon Guinot <simon.guinot@sequanux.org>

Basing on xmit_more flag of the skb, TX descriptors can be concatenated
before flushing. This commit delay Tx descriptor flush if the queue is
running and if there is more skb's to send.

Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
---
 drivers/net/ethernet/marvell/mvneta.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index d41c28d..b9dccea 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -512,6 +512,7 @@ struct mvneta_tx_queue {
 	 * descriptor ring
 	 */
 	int count;
+	int pending;
 	int tx_stop_threshold;
 	int tx_wake_threshold;
 
@@ -802,8 +803,9 @@ static void mvneta_txq_pend_desc_add(struct mvneta_port *pp,
 	/* Only 255 descriptors can be added at once ; Assume caller
 	 * process TX desriptors in quanta less than 256
 	 */
-	val = pend_desc;
+	val = pend_desc + txq->pending;
 	mvreg_write(pp, MVNETA_TXQ_UPDATE_REG(txq->id), val);
+	txq->pending = 0;
 }
 
 /* Get pointer to next TX descriptor to be processed (send) by HW */
@@ -2357,11 +2359,14 @@ out:
 		struct netdev_queue *nq = netdev_get_tx_queue(dev, txq_id);
 
 		txq->count += frags;
-		mvneta_txq_pend_desc_add(pp, txq, frags);
-
 		if (txq->count >= txq->tx_stop_threshold)
 			netif_tx_stop_queue(nq);
 
+		if (!skb->xmit_more || netif_xmit_stopped(nq))
+			mvneta_txq_pend_desc_add(pp, txq, frags);
+		else
+			txq->pending += frags;
+
 		u64_stats_update_begin(&stats->syncp);
 		stats->tx_packets++;
 		stats->tx_bytes  += len;
-- 
1.8.3.1

Re: [PATCH net-next 1/2] net: mvneta: add xmit_more support

[Eric Dumazet]

On Tue, 2016-09-13 at 09:00 +0200, Marcin Wojtas wrote:
> From: Simon Guinot <simon.guinot@sequanux.org>
> 
> Basing on xmit_more flag of the skb, TX descriptors can be concatenated
> before flushing. This commit delay Tx descriptor flush if the queue is
> running and if there is more skb's to send.
> 
> Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
> ---
>  drivers/net/ethernet/marvell/mvneta.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index d41c28d..b9dccea 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -512,6 +512,7 @@ struct mvneta_tx_queue {
>  	 * descriptor ring
>  	 */
>  	int count;
> +	int pending;
>  	int tx_stop_threshold;
>  	int tx_wake_threshold;
>  
> @@ -802,8 +803,9 @@ static void mvneta_txq_pend_desc_add(struct mvneta_port *pp,
>  	/* Only 255 descriptors can be added at once ; Assume caller
>  	 * process TX desriptors in quanta less than 256
>  	 */

Hi Marcin

Well, given the above comment, and fact that MVNETA_MAX_TXD == 532, it
looks like you might add a bug if more than 256 skb are given to your
ndo_start_xmit() with skb->xmit_more = 1

I therefore suggest you make sure it does not happen.

txq->pending += frags;
if (!skb->xmit_more ||
    txq->pending > 256 - MVNETA_MAX_SKB_DESCS ||
    netif_xmit_stopped(nq))
	mvneta_txq_pend_desc_add(pp, txq)

Re: [PATCH net-next 1/2] net: mvneta: add xmit_more support

[Eric Dumazet]

On Tue, 2016-09-13 at 07:33 -0700, Eric Dumazet wrote:

> Hi Marcin
> 
> Well, given the above comment, and fact that MVNETA_MAX_TXD == 532, it
> looks like you might add a bug if more than 256 skb are given to your
> ndo_start_xmit() with skb->xmit_more = 1
> 
> I therefore suggest you make sure it does not happen.
> 
> txq->pending += frags;
> if (!skb->xmit_more ||
>     txq->pending > 256 - MVNETA_MAX_SKB_DESCS ||
>     netif_xmit_stopped(nq))
> 	mvneta_txq_pend_desc_add(pp, txq)
> 

Another solution would be to test the potential overflow in mvneta_tx()
and force a mvneta_txq_pend_desc_add(pp, txq) _before_ adding the desc
of the "about to be cooked" TSO packet.

(This is because MVNETA_MAX_SKB_DESCS is 217, so 255-217 leaves few room
for xmit_more to show its power)

[PATCH net-next 2/2] net: mvneta: add BQL support

[Marcin Wojtas]

Tests showed that when whole bandwidth is consumed, the latency for
various kind of traffic can reach high values. With saturated
link (e.g. with iperf from target to host) simple ping could take
significant amount of time. BQL proved to improve this situation
when implemented in mvneta driver. Measurements of ping latency
for 3 link speeds:
Speed | Latency w/o BQL | Latency with BQL
10    |      7-14 ms    |     3.5 ms
100   |      2-12 ms    |     0.6 ms
1000  |   often timeout |   up to 2ms

Decreasing latency as above result in sligt performance cost - 4kpps
(-1.4%) when pushing 64B packets via two bridged interfaces of Armada 38x.
For 1500B packets in the same setup, the mpstat tool showed +8% of
CPU occupation (default affinity, second CPU idle). Even though this
cost seems reasonable to take, considering other improvements.

This commit adds byte queue limit mechanism for the mvneta driver.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
---
 drivers/net/ethernet/marvell/mvneta.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index b9dccea..bb5df35 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -1719,8 +1719,10 @@ static struct mvneta_tx_queue *mvneta_tx_done_policy(struct mvneta_port *pp,
 
 /* Free tx queue skbuffs */
 static void mvneta_txq_bufs_free(struct mvneta_port *pp,
-				 struct mvneta_tx_queue *txq, int num)
+				 struct mvneta_tx_queue *txq, int num,
+				 struct netdev_queue *nq)
 {
+	unsigned int bytes_compl = 0, pkts_compl = 0;
 	int i;
 
 	for (i = 0; i < num; i++) {
@@ -1728,6 +1730,11 @@ static void mvneta_txq_bufs_free(struct mvneta_port *pp,
 			txq->txq_get_index;
 		struct sk_buff *skb = txq->tx_skb[txq->txq_get_index];
 
+		if (skb) {
+			bytes_compl += skb->len;
+			pkts_compl++;
+		}
+
 		mvneta_txq_inc_get(txq);
 
 		if (!IS_TSO_HEADER(txq, tx_desc->buf_phys_addr))
@@ -1738,6 +1745,8 @@ static void mvneta_txq_bufs_free(struct mvneta_port *pp,
 			continue;
 		dev_kfree_skb_any(skb);
 	}
+
+	netdev_tx_completed_queue(nq, pkts_compl, bytes_compl);
 }
 
 /* Handle end of transmission */
@@ -1751,7 +1760,7 @@ static void mvneta_txq_done(struct mvneta_port *pp,
 	if (!tx_done)
 		return;
 
-	mvneta_txq_bufs_free(pp, txq, tx_done);
+	mvneta_txq_bufs_free(pp, txq, tx_done, nq);
 
 	txq->count -= tx_done;
 
@@ -2358,6 +2367,8 @@ out:
 		struct mvneta_pcpu_stats *stats = this_cpu_ptr(pp->stats);
 		struct netdev_queue *nq = netdev_get_tx_queue(dev, txq_id);
 
+		netdev_tx_sent_queue(nq, len);
+
 		txq->count += frags;
 		if (txq->count >= txq->tx_stop_threshold)
 			netif_tx_stop_queue(nq);
@@ -2385,9 +2396,10 @@ static void mvneta_txq_done_force(struct mvneta_port *pp,
 				  struct mvneta_tx_queue *txq)
 
 {
+	struct netdev_queue *nq = netdev_get_tx_queue(pp->dev, txq->id);
 	int tx_done = txq->count;
 
-	mvneta_txq_bufs_free(pp, txq, tx_done);
+	mvneta_txq_bufs_free(pp, txq, tx_done, nq);
 
 	/* reset txq */
 	txq->count = 0;
@@ -2884,6 +2896,8 @@ static int mvneta_txq_init(struct mvneta_port *pp,
 static void mvneta_txq_deinit(struct mvneta_port *pp,
 			      struct mvneta_tx_queue *txq)
 {
+	struct netdev_queue *nq = netdev_get_tx_queue(pp->dev, txq->id);
+
 	kfree(txq->tx_skb);
 
 	if (txq->tso_hdrs)
@@ -2895,6 +2909,8 @@ static void mvneta_txq_deinit(struct mvneta_port *pp,
 				  txq->size * MVNETA_DESC_ALIGNED_SIZE,
 				  txq->descs, txq->descs_phys);
 
+	netdev_tx_reset_queue(nq);
+
 	txq->descs             = NULL;
 	txq->last_desc         = 0;
 	txq->next_desc_to_proc = 0;
-- 
1.8.3.1