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

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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: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Julian Wiedmann 2020-03-18 13:54:50 +01:00 committed by David S. Miller
parent 66cddf1019
commit 5d8ce41c6a
3 changed files with 46 additions and 2 deletions
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1
drivers/s390/net/qeth_core.h
View file

@ -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);

45
drivers/s390/net/qeth_core_main.c
View file

@ -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;

2
drivers/s390/net/qeth_ethtool.c
View file

@ -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,