netdev - [PATCH v2 net-next 5/6] sfc: rewrite efx_tx_may

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Date:   Thu, 3 Sep 2020 22:35:29 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     <linux-net-drivers@...arflare.com>, <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>
Subject: [PATCH v2 net-next 5/6] sfc: rewrite efx_tx_may_pio

Use efx_for_each_channel_tx_queue() rather than efx_tx_queue_partner().
Make some related simplifications of efx_nic_tx_is_empty() to remove
 entry points that aren't used.

Signed-off-by: Edward Cree <ecree@...arflare.com>
---
 drivers/net/ethernet/sfc/nic_common.h | 30 ++-------------------------
 drivers/net/ethernet/sfc/tx.c         | 26 ++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 29 deletions(-)

diff --git a/drivers/net/ethernet/sfc/nic_common.h b/drivers/net/ethernet/sfc/nic_common.h
index 974107354087..3f88c6444fa1 100644
--- a/drivers/net/ethernet/sfc/nic_common.h
+++ b/drivers/net/ethernet/sfc/nic_common.h
@@ -65,8 +65,7 @@ efx_tx_desc(struct efx_tx_queue *tx_queue, unsigned int index)
 /* Report whether this TX queue would be empty for the given write_count.
  * May return false negative.
  */
-static inline bool __efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue,
-					 unsigned int write_count)
+static inline bool efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue, unsigned int write_count)
 {
 	unsigned int empty_read_count = READ_ONCE(tx_queue->empty_read_count);
 
@@ -76,17 +75,6 @@ static inline bool __efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue,
 	return ((empty_read_count ^ write_count) & ~EFX_EMPTY_COUNT_VALID) == 0;
 }
 
-/* Report whether the NIC considers this TX queue empty, using
- * packet_write_count (the write count recorded for the last completable
- * doorbell push).  May return false negative.  EF10 only, which is OK
- * because only EF10 supports PIO.
- */
-static inline bool efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue)
-{
-	EFX_WARN_ON_ONCE_PARANOID(!tx_queue->efx->type->option_descriptors);
-	return __efx_nic_tx_is_empty(tx_queue, tx_queue->packet_write_count);
-}
-
 /* Get partner of a TX queue, seen as part of the same net core queue */
 /* XXX is this a thing on EF100? */
 static inline struct efx_tx_queue *efx_tx_queue_partner(struct efx_tx_queue *tx_queue)
@@ -97,20 +85,6 @@ static inline struct efx_tx_queue *efx_tx_queue_partner(struct efx_tx_queue *tx_
 		return tx_queue + EFX_TXQ_TYPE_OFFLOAD;
 }
 
-/* Decide whether we can use TX PIO, ie. write packet data directly into
- * a buffer on the device.  This can reduce latency at the expense of
- * throughput, so we only do this if both hardware and software TX rings
- * are empty.  This also ensures that only one packet at a time can be
- * using the PIO buffer.
- */
-static inline bool efx_nic_may_tx_pio(struct efx_tx_queue *tx_queue)
-{
-	struct efx_tx_queue *partner = efx_tx_queue_partner(tx_queue);
-
-	return tx_queue->piobuf && efx_nic_tx_is_empty(tx_queue) &&
-	       efx_nic_tx_is_empty(partner);
-}
-
 int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue, struct sk_buff *skb,
 			bool *data_mapped);
 
@@ -125,7 +99,7 @@ int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue, struct sk_buff *skb,
 static inline bool efx_nic_may_push_tx_desc(struct efx_tx_queue *tx_queue,
 					    unsigned int write_count)
 {
-	bool was_empty = __efx_nic_tx_is_empty(tx_queue, write_count);
+	bool was_empty = efx_nic_tx_is_empty(tx_queue, write_count);
 
 	tx_queue->empty_read_count = 0;
 	return was_empty && tx_queue->write_count - write_count == 1;
diff --git a/drivers/net/ethernet/sfc/tx.c b/drivers/net/ethernet/sfc/tx.c
index b868920b680c..48d91b26f1a2 100644
--- a/drivers/net/ethernet/sfc/tx.c
+++ b/drivers/net/ethernet/sfc/tx.c
@@ -264,6 +264,30 @@ static int efx_enqueue_skb_pio(struct efx_tx_queue *tx_queue,
 	++tx_queue->insert_count;
 	return 0;
 }
+
+/* Decide whether we can use TX PIO, ie. write packet data directly into
+ * a buffer on the device.  This can reduce latency at the expense of
+ * throughput, so we only do this if both hardware and software TX rings
+ * are empty, including all queues for the channel.  This also ensures that
+ * only one packet at a time can be using the PIO buffer. If the xmit_more
+ * flag is set then we don't use this - there'll be another packet along
+ * shortly and we want to hold off the doorbell.
+ */
+static bool efx_tx_may_pio(struct efx_tx_queue *tx_queue)
+{
+	struct efx_channel *channel = tx_queue->channel;
+
+	if (!tx_queue->piobuf)
+		return false;
+
+	EFX_WARN_ON_ONCE_PARANOID(!channel->efx->type->option_descriptors);
+
+	efx_for_each_channel_tx_queue(tx_queue, channel)
+		if (!efx_nic_tx_is_empty(tx_queue, tx_queue->packet_write_count))
+			return false;
+
+	return true;
+}
 #endif /* EFX_USE_PIO */
 
 /* Send any pending traffic for a channel. xmit_more is shared across all
@@ -326,7 +350,7 @@ netdev_tx_t __efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb
 			goto err;
 #ifdef EFX_USE_PIO
 	} else if (skb_len <= efx_piobuf_size && !xmit_more &&
-		   efx_nic_may_tx_pio(tx_queue)) {
+		   efx_tx_may_pio(tx_queue)) {
 		/* Use PIO for short packets with an empty queue. */
 		if (efx_enqueue_skb_pio(tx_queue, skb))
 			goto err;