Commit 5d8ce41c authored by Julian Wiedmann's avatar Julian Wiedmann Committed by David S. Miller
Browse files

s390/qeth: balance the TX queue selection for IQD devices 



For ucast traffic, qeth_iqd_select_queue() falls back to
netdev_pick_tx(). This will potentially use skb_tx_hash() to distribute
the flow over all active TX queues - so txq 0 is a valid selection, and
qeth_iqd_select_queue() needs to check for this and put it on some other
queue. As a result, the distribution for ucast flows is unbalanced and
hits QETH_IQD_MIN_UCAST_TXQ heavier than the other queues.

Open-coding a custom variant of skb_tx_hash() isn't an option, since
netdev_pick_tx() also gives us eg. access to XPS. But we can pull a
little trick: add a single TC class that excludes the mcast txq, and
thus encourage skb_tx_hash() to not pick the mcast txq.

Signed-off-by: default avatarJulian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 66cddf10

drivers/s390/net/qeth_core.h

+1 −0
Original line number Diff line number Diff line
@@ -1061,6 +1061,7 @@ netdev_features_t qeth_features_check(struct sk_buff *skb, 
				      struct net_device *dev,

				      netdev_features_t features);

void qeth_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats);

int qeth_set_real_num_tx_queues(struct qeth_card *card, unsigned int count);

u16 qeth_iqd_select_queue(struct net_device *dev, struct sk_buff *skb,

			  u8 cast_type, struct net_device *sb_dev);

int qeth_open(struct net_device *dev);

drivers/s390/net/qeth_core_main.c

+44 −1
Original line number Diff line number Diff line
@@ -6025,7 +6025,7 @@ int qeth_setup_netdev(struct qeth_card *card) 
		num_tx_queues = dev->real_num_tx_queues;

	}



	return netif_set_real_num_tx_queues(dev, num_tx_queues);

	return qeth_set_real_num_tx_queues(card, num_tx_queues);

}

EXPORT_SYMBOL_GPL(qeth_setup_netdev);
@@ -6641,6 +6641,47 @@ void qeth_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats) 
}

EXPORT_SYMBOL_GPL(qeth_get_stats64);



#define TC_IQD_UCAST   0

static void qeth_iqd_set_prio_tc_map(struct net_device *dev,

				     unsigned int ucast_txqs)

{

	unsigned int prio;



	/* IQD requires mcast traffic to be placed on a dedicated queue, and

	 * qeth_iqd_select_queue() deals with this.

	 * For unicast traffic, we defer the queue selection to the stack.

	 * By installing a trivial prio map that spans over only the unicast

	 * queues, we can encourage the stack to spread the ucast traffic evenly

	 * without selecting the mcast queue.

	 */



	/* One traffic class, spanning over all active ucast queues: */

	netdev_set_num_tc(dev, 1);

	netdev_set_tc_queue(dev, TC_IQD_UCAST, ucast_txqs,

			    QETH_IQD_MIN_UCAST_TXQ);



	/* Map all priorities to this traffic class: */

	for (prio = 0; prio <= TC_BITMASK; prio++)

		netdev_set_prio_tc_map(dev, prio, TC_IQD_UCAST);

}



int qeth_set_real_num_tx_queues(struct qeth_card *card, unsigned int count)

{

	struct net_device *dev = card->dev;

	int rc;



	/* Per netif_setup_tc(), adjust the mapping first: */

	if (IS_IQD(card))

		qeth_iqd_set_prio_tc_map(dev, count - 1);



	rc = netif_set_real_num_tx_queues(dev, count);



	if (rc && IS_IQD(card))

		qeth_iqd_set_prio_tc_map(dev, dev->real_num_tx_queues - 1);



	return rc;

}



u16 qeth_iqd_select_queue(struct net_device *dev, struct sk_buff *skb,

			  u8 cast_type, struct net_device *sb_dev)

{
@@ -6648,6 +6689,8 @@ u16 qeth_iqd_select_queue(struct net_device *dev, struct sk_buff *skb, 


	if (cast_type != RTN_UNICAST)

		return QETH_IQD_MCAST_TXQ;

	if (dev->real_num_tx_queues == QETH_IQD_MIN_TXQ)

		return QETH_IQD_MIN_UCAST_TXQ;



	txq = netdev_pick_tx(dev, skb, sb_dev);

	return (txq == QETH_IQD_MCAST_TXQ) ? QETH_IQD_MIN_UCAST_TXQ : txq;

drivers/s390/net/qeth_ethtool.c

+1 −1
Original line number Diff line number Diff line
@@ -201,7 +201,7 @@ static int qeth_set_channels(struct net_device *dev, 
			return -EOPNOTSUPP;

	}



	return netif_set_real_num_tx_queues(dev, channels->tx_count);

	return qeth_set_real_num_tx_queues(card, channels->tx_count);

}



static int qeth_get_tunable(struct net_device *dev,

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