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

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>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h
index 4989dc7b58c1..fbaf434e2e34 100644
--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -481,6 +481,7 @@ struct qeth_out_q_stats {
 	u64 skbs_linearized_fail;
 	u64 tso_bytes;
 	u64 packing_mode_switch;
+	u64 stopped;
 
 	/* rtnl_link_stats64 */
 	u64 tx_packets;
@@ -511,6 +512,11 @@ struct qeth_qdio_out_q {
 	atomic_t set_pci_flags_count;
 };
 
+static inline bool qeth_out_queue_is_full(struct qeth_qdio_out_q *queue)
+{
+	return atomic_read(&queue->used_buffers) >= QDIO_MAX_BUFFERS_PER_Q;
+}
+
 struct qeth_qdio_info {
 	atomic_t state;
 	/* input */