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s390/qeth: stop/wake TX queues based on their fill level

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Current xmit code only stops the txq after attempting to fill an
IO buffer that hasn't been TX-completed yet. In many-connection
scenarios, this can result in frequent rejected TX attempts, requeuing
of skbs with NETDEV_TX_BUSY and extra overhead.

Now that we have a proper 1-to-1 relation between stack-side txqs and
our HW Queues, overhaul the stop/wake logic so that the xmit code
stops the txq as needed.
Given that we might map multiple skbs into a single buffer, it's crucial
to ensure that the queue always provides an _entirely_ empty IO buffer.
Otherwise large skbs (eg TSO) might not fit into the last available
buffer. So whenever qeth_do_send_packet() first utilizes an _empty_
buffer, it updates & checks the used_buffers count.

This now ensures that an skb passed to qeth_xmit() can always be mapped
into an IO buffer, so remove all of the -EBUSY roll-back handling in the
TX path. We preserve the minimal safety-checks ("Is this IO buffer
really available?"), just in case some nasty future bug ever attempts to
corrupt an in-use buffer.

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
2019-04-17 18:17:35 +02:00
committed by David S. Miller
parent e6c15b5f34
commit 54a50941b7
5 changed files with 71 additions and 48 deletions
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18
drivers/s390/net/qeth_l3_main.c
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@@ -2036,7 +2036,6 @@ static void qeth_l3_fixup_headers(struct sk_buff *skb)
static int qeth_l3_xmit(struct qeth_card *card, struct sk_buff *skb,
struct qeth_qdio_out_q *queue, int ipv, int cast_type)
{
unsigned char eth_hdr[ETH_HLEN];
unsigned int hw_hdr_len;
int rc;
@@ -2046,17 +2045,10 @@ static int qeth_l3_xmit(struct qeth_card *card, struct sk_buff *skb,
rc = skb_cow_head(skb, hw_hdr_len - ETH_HLEN);
if (rc)
return rc;
skb_copy_from_linear_data(skb, eth_hdr, ETH_HLEN);
skb_pull(skb, ETH_HLEN);
qeth_l3_fixup_headers(skb);
rc = qeth_xmit(card, skb, queue, ipv, cast_type, qeth_l3_fill_header);
if (rc == -EBUSY) {
/* roll back to ETH header */
skb_push(skb, ETH_HLEN);
skb_copy_to_linear_data(skb, eth_hdr, ETH_HLEN);
}
return rc;
return qeth_xmit(card, skb, queue, ipv, cast_type, qeth_l3_fill_header);
}
static netdev_tx_t qeth_l3_hard_start_xmit(struct sk_buff *skb,
@@ -2091,8 +2083,6 @@ static netdev_tx_t qeth_l3_hard_start_xmit(struct sk_buff *skb,
if (cast_type == RTN_BROADCAST && !card->info.broadcast_capable)
goto tx_drop;
netif_stop_subqueue(dev, txq);
if (ipv == 4 || IS_IQD(card))
rc = qeth_l3_xmit(card, skb, queue, ipv, cast_type);
else
@@ -2102,16 +2092,12 @@ static netdev_tx_t qeth_l3_hard_start_xmit(struct sk_buff *skb,
if (!rc) {
QETH_TXQ_STAT_INC(queue, tx_packets);
QETH_TXQ_STAT_ADD(queue, tx_bytes, tx_bytes);
netif_wake_subqueue(dev, txq);
return NETDEV_TX_OK;
} else if (rc == -EBUSY) {
return NETDEV_TX_BUSY;
} /* else fall through */
}
tx_drop:
QETH_TXQ_STAT_INC(queue, tx_dropped);
kfree_skb(skb);
netif_wake_subqueue(dev, txq);
return NETDEV_TX_OK;
}