Merge branch 'sfc-TXQ-refactor'

Edward Cree says:

====================
sfc: TXQ refactor

Refactor and unify partner-TXQ handling in the EF100 and legacy drivers.

The main thrust of this series is to remove from the legacy (Siena/EF10)
 driver the assumption that a netdev TX queue has precisely two hardware
 TXQs (checksummed and unchecksummed) associated with it, so that in
 future we can have more (e.g. for handling inner-header checksums) or
 fewer (e.g. to free up hardware queues for XDP usage).

Changes from v1:
 * better explain patch #1 in the commit message, and rename
   xmit_more_available to xmit_pending
 * add new patch #2 applying the same approach to ef100, for consistency
====================

Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/sfc/ef10.c

@@ -2367,7 +2367,7 @@ static void efx_ef10_tx_write(struct efx_tx_queue *tx_queue)
 	unsigned int write_ptr;
 	efx_qword_t *txd;
 
-	tx_queue->xmit_more_available = false;
+	tx_queue->xmit_pending = false;
 	if (unlikely(tx_queue->write_count == tx_queue->insert_count))
 		return;
 

drivers/net/ethernet/sfc/ef100_tx.c

@@ -117,11 +117,13 @@ static efx_oword_t *ef100_tx_desc(struct efx_tx_queue *tx_queue, unsigned int in
 		return NULL;
 }
 
-void ef100_notify_tx_desc(struct efx_tx_queue *tx_queue)
+static void ef100_notify_tx_desc(struct efx_tx_queue *tx_queue)
 {
 	unsigned int write_ptr;
 	efx_dword_t reg;
 
+	tx_queue->xmit_pending = false;
+
 	if (unlikely(tx_queue->notify_count == tx_queue->write_count))
 		return;
 
@@ -131,7 +133,6 @@ void ef100_notify_tx_desc(struct efx_tx_queue *tx_queue)
 	efx_writed_page(tx_queue->efx, &reg,
 			ER_GZ_TX_RING_DOORBELL, tx_queue->queue);
 	tx_queue->notify_count = tx_queue->write_count;
-	tx_queue->xmit_more_available = false;
 }
 
 static void ef100_tx_push_buffers(struct efx_tx_queue *tx_queue)
@@ -359,28 +360,31 @@ int ef100_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
 		goto err;
 	ef100_tx_make_descriptors(tx_queue, skb, segments);
 
-	fill_level = efx_channel_tx_fill_level(tx_queue->channel);
+	fill_level = efx_channel_tx_old_fill_level(tx_queue->channel);
 	if (fill_level > efx->txq_stop_thresh) {
+		struct efx_tx_queue *txq2;
+
 		netif_tx_stop_queue(tx_queue->core_txq);
 		/* Re-read after a memory barrier in case we've raced with
 		 * the completion path. Otherwise there's a danger we'll never
 		 * restart the queue if all completions have just happened.
 		 */
 		smp_mb();
-		fill_level = efx_channel_tx_fill_level(tx_queue->channel);
+		efx_for_each_channel_tx_queue(txq2, tx_queue->channel)
+			txq2->old_read_count = READ_ONCE(txq2->read_count);
+		fill_level = efx_channel_tx_old_fill_level(tx_queue->channel);
 		if (fill_level < efx->txq_stop_thresh)
 			netif_tx_start_queue(tx_queue->core_txq);
 	}
 
-	if (__netdev_tx_sent_queue(tx_queue->core_txq, skb->len, xmit_more))
-		tx_queue->xmit_more_available = false; /* push doorbell */
-	else if (tx_queue->write_count - tx_queue->notify_count > 255)
-		/* Ensure we never push more than 256 packets at once */
-		tx_queue->xmit_more_available = false; /* push */
-	else
-		tx_queue->xmit_more_available = true; /* don't push yet */
+	tx_queue->xmit_pending = true;
 
-	if (!tx_queue->xmit_more_available)
+	/* If xmit_more then we don't need to push the doorbell, unless there
+	 * are 256 descriptors already queued in which case we have to push to
+	 * ensure we never push more than 256 at once.
+	 */
+	if (__netdev_tx_sent_queue(tx_queue->core_txq, skb->len, xmit_more) ||
+	    tx_queue->write_count - tx_queue->notify_count > 255)
 		ef100_tx_push_buffers(tx_queue);
 
 	if (segments) {
@@ -399,10 +403,10 @@ int ef100_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
 
 	/* If we're not expecting another transmit and we had something to push
 	 * on this queue then we need to push here to get the previous packets
-	 * out.  We only enter this branch from before the 'Update BQL' section
-	 * above, so xmit_more_available still refers to the old state.
+	 * out.  We only enter this branch from before the xmit_more handling
+	 * above, so xmit_pending still refers to the old state.
 	 */
-	if (tx_queue->xmit_more_available && !xmit_more)
+	if (tx_queue->xmit_pending && !xmit_more)
 		ef100_tx_push_buffers(tx_queue);
 	return rc;
 }

drivers/net/ethernet/sfc/ef100_tx.h

@@ -17,7 +17,6 @@
 int ef100_tx_probe(struct efx_tx_queue *tx_queue);
 void ef100_tx_init(struct efx_tx_queue *tx_queue);
 void ef100_tx_write(struct efx_tx_queue *tx_queue);
-void ef100_notify_tx_desc(struct efx_tx_queue *tx_queue);
 unsigned int ef100_tx_max_skb_descs(struct efx_nic *efx);
 
 void ef100_ev_tx(struct efx_channel *channel, const efx_qword_t *p_event);

drivers/net/ethernet/sfc/farch.c

@@ -320,7 +320,7 @@ void efx_farch_tx_write(struct efx_tx_queue *tx_queue)
 	unsigned write_ptr;
 	unsigned old_write_count = tx_queue->write_count;
 
-	tx_queue->xmit_more_available = false;
+	tx_queue->xmit_pending = false;
 	if (unlikely(tx_queue->write_count == tx_queue->insert_count))
 		return;
 

drivers/net/ethernet/sfc/net_driver.h

@@ -244,7 +244,7 @@ struct efx_tx_buffer {
  * @tso_fallbacks: Number of times TSO fallback used
  * @pushes: Number of times the TX push feature has been used
  * @pio_packets: Number of times the TX PIO feature has been used
- * @xmit_more_available: Are any packets waiting to be pushed to the NIC
+ * @xmit_pending: Are any packets waiting to be pushed to the NIC
  * @cb_packets: Number of times the TX copybreak feature has been used
  * @notify_count: Count of notified descriptors to the NIC
  * @empty_read_count: If the completion path has seen the queue as empty
@@ -292,7 +292,7 @@ struct efx_tx_queue {
 	unsigned int tso_fallbacks;
 	unsigned int pushes;
 	unsigned int pio_packets;
-	bool xmit_more_available;
+	bool xmit_pending;
 	unsigned int cb_packets;
 	unsigned int notify_count;
 	/* Statistics to supplement MAC stats */
@@ -1681,17 +1681,27 @@ efx_channel_tx_fill_level(struct efx_channel *channel)
 	struct efx_tx_queue *tx_queue;
 	unsigned int fill_level = 0;
 
-	/* This function is currently only used by EF100, which maybe
-	 * could do something simpler and just compute the fill level
-	 * of the single TXQ that's really in use.
-	 */
 	efx_for_each_channel_tx_queue(tx_queue, channel)
 		fill_level = max(fill_level,
 				 tx_queue->insert_count - tx_queue->read_count);
 
 	return fill_level;
 }
 
+/* Conservative approximation of efx_channel_tx_fill_level using cached value */
+static inline unsigned int
+efx_channel_tx_old_fill_level(struct efx_channel *channel)
+{
+	struct efx_tx_queue *tx_queue;
+	unsigned int fill_level = 0;
+
+	efx_for_each_channel_tx_queue(tx_queue, channel)
+		fill_level = max(fill_level,
+				 tx_queue->insert_count - tx_queue->old_read_count);
+
+	return fill_level;
+}
+
 /* Get all supported features.
  * If a feature is not fixed, it is present in hw_features.
  * If a feature is fixed, it does not present in hw_features, but

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);
 
@@ -76,41 +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)
-{
-	if (tx_queue->label & EFX_TXQ_TYPE_OFFLOAD)
-		return tx_queue - EFX_TXQ_TYPE_OFFLOAD;
-	else
-		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 +89,7 @@ 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;

drivers/net/ethernet/sfc/tx.c

@@ -59,13 +59,12 @@ u8 *efx_tx_get_copy_buffer_limited(struct efx_tx_queue *tx_queue,
 
 static void efx_tx_maybe_stop_queue(struct efx_tx_queue *txq1)
 {
-	/* We need to consider both queues that the net core sees as one */
-	struct efx_tx_queue *txq2 = efx_tx_queue_partner(txq1);
+	/* We need to consider all queues that the net core sees as one */
 	struct efx_nic *efx = txq1->efx;
+	struct efx_tx_queue *txq2;
 	unsigned int fill_level;
 
-	fill_level = max(txq1->insert_count - txq1->old_read_count,
-			 txq2->insert_count - txq2->old_read_count);
+	fill_level = efx_channel_tx_old_fill_level(txq1->channel);
 	if (likely(fill_level < efx->txq_stop_thresh))
 		return;
 
@@ -85,11 +84,10 @@ static void efx_tx_maybe_stop_queue(struct efx_tx_queue *txq1)
 	 */
 	netif_tx_stop_queue(txq1->core_txq);
 	smp_mb();
-	txq1->old_read_count = READ_ONCE(txq1->read_count);
-	txq2->old_read_count = READ_ONCE(txq2->read_count);
+	efx_for_each_channel_tx_queue(txq2, txq1->channel)
+		txq2->old_read_count = READ_ONCE(txq2->read_count);
 
-	fill_level = max(txq1->insert_count - txq1->old_read_count,
-			 txq2->insert_count - txq2->old_read_count);
+	fill_level = efx_channel_tx_old_fill_level(txq1->channel);
 	EFX_WARN_ON_ONCE_PARANOID(fill_level >= efx->txq_entries);
 	if (likely(fill_level < efx->txq_stop_thresh)) {
 		smp_mb();
@@ -266,8 +264,45 @@ 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
+ * queues for a channel, so we must check all of them.
+ */
+static void efx_tx_send_pending(struct efx_channel *channel)
+{
+	struct efx_tx_queue *q;
+
+	efx_for_each_channel_tx_queue(q, channel) {
+		if (q->xmit_pending)
+			efx_nic_push_buffers(q);
+	}
+}
+
 /*
  * Add a socket buffer to a TX queue
  *
@@ -315,7 +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;
@@ -336,21 +371,11 @@ netdev_tx_t __efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb
 
 	efx_tx_maybe_stop_queue(tx_queue);
 
-	/* Pass off to hardware */
-	if (__netdev_tx_sent_queue(tx_queue->core_txq, skb_len, xmit_more)) {
-		struct efx_tx_queue *txq2 = efx_tx_queue_partner(tx_queue);
-
-		/* There could be packets left on the partner queue if
-		 * xmit_more was set. If we do not push those they
-		 * could be left for a long time and cause a netdev watchdog.
-		 */
-		if (txq2->xmit_more_available)
-			efx_nic_push_buffers(txq2);
+	tx_queue->xmit_pending = true;
 
-		efx_nic_push_buffers(tx_queue);
-	} else {
-		tx_queue->xmit_more_available = xmit_more;
-	}
+	/* Pass off to hardware */
+	if (__netdev_tx_sent_queue(tx_queue->core_txq, skb_len, xmit_more))
+		efx_tx_send_pending(tx_queue->channel);
 
 	if (segments) {
 		tx_queue->tso_bursts++;
@@ -371,14 +396,8 @@ netdev_tx_t __efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb
 	 * on this queue or a partner queue then we need to push here to get the
 	 * previous packets out.
 	 */
-	if (!xmit_more) {
-		struct efx_tx_queue *txq2 = efx_tx_queue_partner(tx_queue);
-
-		if (txq2->xmit_more_available)
-			efx_nic_push_buffers(txq2);
-
-		efx_nic_push_buffers(tx_queue);
-	}
+	if (!xmit_more)
+		efx_tx_send_pending(tx_queue->channel);
 
 	return NETDEV_TX_OK;
 }
@@ -489,18 +508,24 @@ netdev_tx_t efx_hard_start_xmit(struct sk_buff *skb,
 
 	EFX_WARN_ON_PARANOID(!netif_device_present(net_dev));
 
-	/* PTP "event" packet */
-	if (unlikely(efx_xmit_with_hwtstamp(skb)) &&
-	    unlikely(efx_ptp_is_ptp_tx(efx, skb))) {
-		return efx_ptp_tx(efx, skb);
-	}
-
 	index = skb_get_queue_mapping(skb);
 	type = skb->ip_summed == CHECKSUM_PARTIAL ? EFX_TXQ_TYPE_OFFLOAD : 0;
 	if (index >= efx->n_tx_channels) {
 		index -= efx->n_tx_channels;
 		type |= EFX_TXQ_TYPE_HIGHPRI;
 	}
+
+	/* PTP "event" packet */
+	if (unlikely(efx_xmit_with_hwtstamp(skb)) &&
+	    unlikely(efx_ptp_is_ptp_tx(efx, skb))) {
+		/* There may be existing transmits on the channel that are
+		 * waiting for this packet to trigger the doorbell write.
+		 * We need to send the packets at this point.
+		 */
+		efx_tx_send_pending(efx_get_tx_channel(efx, index));
+		return efx_ptp_tx(efx, skb);
+	}
+
 	tx_queue = efx_get_tx_queue(efx, index, type);
 
 	return __efx_enqueue_skb(tx_queue, skb);