net: mvneta: prefetch next rx descriptor instead of current one

Currently, the mvneta driver tries to prefetch the current Rx
descriptor during read. Tests have shown that prefetching the
next one instead increases general performance by about 1% on
HTTP traffic.

Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Gregory CLEMENT <gregory.clement@free-electrons.com>
Tested-by: NArnaud Ebalard <arno@natisbad.org>
Signed-off-by: NWilly Tarreau <w@1wt.eu>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvneta.c

@@ -611,6 +611,7 @@ mvneta_rxq_next_desc_get(struct mvneta_rx_queue *rxq)
 	int rx_desc = rxq->next_desc_to_proc;
 
 	rxq->next_desc_to_proc = MVNETA_QUEUE_NEXT_DESC(rxq, rx_desc);
+	prefetch(rxq->descs + rxq->next_desc_to_proc);
 	return rxq->descs + rx_desc;
 }
 
@@ -1442,7 +1443,6 @@ static int mvneta_rx(struct mvneta_port *pp, int rx_todo,
 		u32 rx_status;
 		int rx_bytes, err;
 
-		prefetch(rx_desc);
 		rx_done++;
 		rx_filled++;
 		rx_status = rx_desc->status;