s390/qeth: add TX NAPI support for IQD devices

Due to their large MTU and potentially low utilization of TX buffers,
IQD devices in particular require fast TX recycling. This makes them
a prime candidate for a TX NAPI path in qeth.

qeth_tx_poll() uses the recently introduced qdio_inspect_queue() helper
to poll the TX queue for completed buffers. To avoid hogging the CPU for
too long, we yield to the stack after completing an entire queue's worth
of buffers.
While IQD is expected to transfer its buffers synchronously (and thus
doesn't support TX interrupts), a timer covers for the odd case where a
TX buffer doesn't complete synchronously. Currently this timer should
only ever fire for
(1) the mcast queue,
(2) the occasional race, where the NAPI poll code observes an update to
    queue->used_buffers while the TX doorbell hasn't been issued yet.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 26 insertions, 0 deletions

diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h
index a0911ce55db3..ae2ae17e3e76 100644
--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -22,6 +22,7 @@
 #include <linux/hashtable.h>
 #include <linux/ip.h>
 #include <linux/refcount.h>
+#include <linux/timer.h>
 #include <linux/wait.h>
 #include <linux/workqueue.h>
 
@@ -474,6 +475,8 @@ struct qeth_out_q_stats {
 	u64 tso_bytes;
 	u64 packing_mode_switch;
 	u64 stopped;
+	u64 completion_yield;
+	u64 completion_timer;
 
 	/* rtnl_link_stats64 */
 	u64 tx_packets;
@@ -482,6 +485,8 @@ struct qeth_out_q_stats {
 	u64 tx_dropped;
 };
 
+#define QETH_TX_TIMER_USECS		500
+
 struct qeth_qdio_out_q {
 	struct qdio_buffer *qdio_bufs[QDIO_MAX_BUFFERS_PER_Q];
 	struct qeth_qdio_out_buffer *bufs[QDIO_MAX_BUFFERS_PER_Q];
@@ -500,13 +505,34 @@ struct qeth_qdio_out_q {
 	atomic_t used_buffers;
 	/* indicates whether PCI flag must be set (or if one is outstanding) */
 	atomic_t set_pci_flags_count;
+	struct napi_struct napi;
+	struct timer_list timer;
 };
 
+#define qeth_for_each_output_queue(card, q, i)		\
+	for (i = 0; i < card->qdio.no_out_queues &&	\
+		    (q = card->qdio.out_qs[i]); i++)
+
+#define	qeth_napi_to_out_queue(n) container_of(n, struct qeth_qdio_out_q, napi)
+
+static inline void qeth_tx_arm_timer(struct qeth_qdio_out_q *queue)
+{
+	if (timer_pending(&queue->timer))
+		return;
+	mod_timer(&queue->timer, usecs_to_jiffies(QETH_TX_TIMER_USECS) +
+				 jiffies);
+}
+
 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;
 }
 
+static inline bool qeth_out_queue_is_empty(struct qeth_qdio_out_q *queue)
+{
+	return atomic_read(&queue->used_buffers) == 0;
+}
+
 struct qeth_qdio_info {
 	atomic_t state;
 	/* input */