[dpdk-dev] [PATCH v2] net/thunderx: avoid sq door bell writes on zero packets

[Kiran Kumar <kkokkilagadda@caviumnetworks.com>]

Avoid sq door bell write on zero packet case to reduce additional
traffic on register bus.

Fixes: 1c421f18e0 ("net/thunderx: add single and multi-segment Tx")
Cc: stable@dpdk.org

Signed-off-by: Kiran Kumar <kkokkilagadda@caviumnetworks.com>
---
 v2 Changes:
 - changed summery and description.
 - added same optimization to nicvf_xmit_pkts_multiseg

 drivers/net/thunderx/nicvf_rxtx.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/net/thunderx/nicvf_rxtx.c b/drivers/net/thunderx/nicvf_rxtx.c
index 72305d9..6e075e2 100644
--- a/drivers/net/thunderx/nicvf_rxtx.c
+++ b/drivers/net/thunderx/nicvf_rxtx.c
@@ -162,12 +162,14 @@ nicvf_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 		free_desc -= TX_DESC_PER_PKT;
 	}

-	sq->tail = tail;
-	sq->xmit_bufs += i;
-	rte_wmb();
+	if (likely(i)) {
+		sq->tail = tail;
+		sq->xmit_bufs += i;
+		rte_wmb();

-	/* Inform HW to xmit the packets */
-	nicvf_addr_write(sq->sq_door, i * TX_DESC_PER_PKT);
+		/* Inform HW to xmit the packets */
+		nicvf_addr_write(sq->sq_door, i * TX_DESC_PER_PKT);
+	}
 	return i;
 }

@@ -218,12 +220,14 @@ nicvf_xmit_pkts_multiseg(void *tx_queue, struct rte_mbuf **tx_pkts,
 		}
 	}

-	sq->tail = tail;
-	sq->xmit_bufs += used_bufs;
-	rte_wmb();
+	if (likely(used_desc)) {
+		sq->tail = tail;
+		sq->xmit_bufs += used_bufs;
+		rte_wmb();

-	/* Inform HW to xmit the packets */
-	nicvf_addr_write(sq->sq_door, used_desc);
+		/* Inform HW to xmit the packets */
+		nicvf_addr_write(sq->sq_door, used_desc);
+	}
 	return i;
 }

--
2.7.4