dpaa2-eth: Don't use multiple queues per channel

The DPNI object on which we build a network interface has a
certain number of {Rx, Tx, Tx confirmation} frame queues as
resources. The default hardware setup offers one queue of each
type, as well as one DPCON channel, for each core available
in the system.

There are however cases where the number of queues is greater
than the number of cores or channels. Until now, we configured
and used all the frame queues associated with a DPNI, even if it
meant assigning multiple queues of one type to the same channel.

Update the driver to only use a number of queues equal to the
number of channels, ensuring each channel will contain exactly
one Rx and one Tx confirmation queue.

>From the user viewpoint, this change is completely transparent.
Performance wise there is no impact in most scenarios. In case
the number of queues is larger than and not a multiple of the
number of channels, Rx hash distribution offers now better load
balancing between cores, which can have a positive impact on
overall system performance.

Signed-off-by: Ioana Radulescu <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c

@@ -1603,7 +1603,7 @@ static int setup_dpio(struct dpaa2_eth_priv *priv)
 		/* Stop if we already have enough channels to accommodate all
 		 * RX and TX conf queues
 		 */
-		if (priv->num_channels == dpaa2_eth_queue_count(priv))
+		if (priv->num_channels == priv->dpni_attrs.num_queues)
 			break;
 	}
 

drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.h

@@ -434,9 +434,10 @@ static inline unsigned int dpaa2_eth_rx_head_room(struct dpaa2_eth_priv *priv)
 	       DPAA2_ETH_RX_HWA_SIZE;
 }
 
+/* We have exactly one {Rx, Tx conf} queue per channel */
 static int dpaa2_eth_queue_count(struct dpaa2_eth_priv *priv)
 {
-	return priv->dpni_attrs.num_queues;
+	return priv->num_channels;
 }
 
 int dpaa2_eth_set_hash(struct net_device *net_dev, u64 flags);