diff mbox series

[net-next,1/5] sfc: add and use efx_tx_send_pending in tx.c

Message ID 1edd44e5-a73a-149f-fe0c-96969627d211@solarflare.com
State Changes Requested
Delegated to: David Miller
Headers show
Series sfc: TXQ refactor | expand

Commit Message

Edward Cree Sept. 2, 2020, 2:35 p.m. UTC 
Instead of using efx_tx_queue_partner(), which relies on the assumption
 that tx_queues_per_channel is 2, efx_tx_send_pending() iterates over
 txqs with efx_for_each_channel_tx_queue().

Signed-off-by: Edward Cree <ecree@solarflare.com>
---
 drivers/net/ethernet/sfc/tx.c | 59 ++++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 28 deletions(-)

Comments

David Miller Sept. 2, 2020, 10:55 p.m. UTC | #1 
From: Edward Cree <ecree@solarflare.com>
Date: Wed, 2 Sep 2020 15:35:53 +0100

> +	tx_queue->xmit_more_available = true;

I don't understand why you're setting xmit_more_available
unconditionally to true now instead of setting it to 'xmit_more' as
seen by this transmit attempt.  Why would you want to signal
that xmit_more handling might be necessary when you haven't been
given an xmit_more tx request?

If this change is in fact correct, it's something you need to explain
in the commit message.
Edward Cree Sept. 3, 2020, 4:48 p.m. UTC | #2 
On 02/09/2020 23:55, David Miller wrote:
> From: Edward Cree <ecree@solarflare.com>
> Date: Wed, 2 Sep 2020 15:35:53 +0100
> 
>> +	tx_queue->xmit_more_available = true;
> 
> I don't understand why you're setting xmit_more_available
> unconditionally to true now instead of setting it to 'xmit_more' as
> seen by this transmit attempt.  Why would you want to signal
> that xmit_more handling might be necessary when you haven't been
> given an xmit_more tx request?

After this patch xmit_more_available is something of a misnomer and
 really means "xmit pending" (I'll rename it in v2).  We unconditionally
 set it to true here so that efx_tx_send_pending() knows there is
 something to do on this queue; but then we only call efx_tx_send_pending
 if !xmit_more (per the __netdev_tx_sent_queue() call).  Then
 efx_tx_send_pending, via the efx->type->tx_write methods, sets
 xmit_more_available to false.
Thus xmit_more_available is only true on return from __efx_enqueue_skb()
 if we had xmit_more (and __netdev_tx_sent_queue didn't say "ring it
 anyway").

> If this change is in fact correct, it's something you need to explain
> in the commit message.
Will do so for v2, as it is indeed far from obvious.

-ed
diff mbox series

Patch

diff --git a/drivers/net/ethernet/sfc/tx.c b/drivers/net/ethernet/sfc/tx.c
index 727201d5eb24..71eb99db5439 100644
--- a/drivers/net/ethernet/sfc/tx.c
+++ b/drivers/net/ethernet/sfc/tx.c
@@ -268,6 +268,19 @@  static int efx_enqueue_skb_pio(struct efx_tx_queue *tx_queue,
 }
 #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_more_available)
+			efx_nic_push_buffers(q);
+	}
+}
+
 /*
  * Add a socket buffer to a TX queue
  *
@@ -336,21 +349,11 @@  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_more_available = 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 +374,8 @@  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 +486,24 @@  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);