[dpdk-dev] [PATCH v4 2/6] vmxnet3: restore tx data ring support

[Yong Wang <yongwang@vmware.com>]

Tx data ring support was removed in a previous change that
added multi-seg transmit.  This change adds it back.

According to the original commit (2e849373), 64B pkt
rate with l2fwd improved by ~20% on an Ivy Bridge
server at which point we start to hit some bottleneck
on the rx side.

I also re-did the same test on a different setup (Haswell
processor, ~2.3GHz clock rate) on top of the master
and still observed ~17% performance gains.

Fixes: 7ba5de417e3c ("vmxnet3: support multi-segment transmit")

Signed-off-by: Yong Wang <yongwang@vmware.com>
---
 doc/guides/rel_notes/release_2_3.rst |  5 +++++
 drivers/net/vmxnet3/vmxnet3_rxtx.c   | 17 ++++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/doc/guides/rel_notes/release_2_3.rst b/doc/guides/rel_notes/release_2_3.rst
index 99de186..a23c8ac 100644
--- a/doc/guides/rel_notes/release_2_3.rst
+++ b/doc/guides/rel_notes/release_2_3.rst
@@ -15,6 +15,11 @@ EAL
 Drivers
 ~~~~~~~
 
+* **vmxnet3: restore tx data ring.**
+
+  Tx data ring has been shown to improve small pkt forwarding performance
+  on vSphere environment.
+
 
 Libraries
 ~~~~~~~~~
diff --git a/drivers/net/vmxnet3/vmxnet3_rxtx.c b/drivers/net/vmxnet3/vmxnet3_rxtx.c
index a3154bc..4ccab0e 100644
--- a/drivers/net/vmxnet3/vmxnet3_rxtx.c
+++ b/drivers/net/vmxnet3/vmxnet3_rxtx.c
@@ -348,6 +348,7 @@ vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 		uint32_t first2fill, avail, dw2;
 		struct rte_mbuf *txm = tx_pkts[nb_tx];
 		struct rte_mbuf *m_seg = txm;
+		int copy_size = 0;
 
 		/* Is this packet execessively fragmented, then drop */
 		if (unlikely(txm->nb_segs > VMXNET3_MAX_TXD_PER_PKT)) {
@@ -365,6 +366,14 @@ vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 			break;
 		}
 
+		if (txm->nb_segs == 1 && rte_pktmbuf_pkt_len(txm) <= VMXNET3_HDR_COPY_SIZE) {
+			struct Vmxnet3_TxDataDesc *tdd;
+
+			tdd = txq->data_ring.base + txq->cmd_ring.next2fill;
+			copy_size = rte_pktmbuf_pkt_len(txm);
+			rte_memcpy(tdd->data, rte_pktmbuf_mtod(txm, char *), copy_size);
+		}
+
 		/* use the previous gen bit for the SOP desc */
 		dw2 = (txq->cmd_ring.gen ^ 0x1) << VMXNET3_TXD_GEN_SHIFT;
 		first2fill = txq->cmd_ring.next2fill;
@@ -377,7 +386,13 @@ vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 			   transmit buffer size (16K) is greater than
 			   maximum sizeof mbuf segment size. */
 			gdesc = txq->cmd_ring.base + txq->cmd_ring.next2fill;
-			gdesc->txd.addr = RTE_MBUF_DATA_DMA_ADDR(m_seg);
+			if (copy_size)
+				gdesc->txd.addr = rte_cpu_to_le_64(txq->data_ring.basePA +
+								txq->cmd_ring.next2fill *
+								sizeof(struct Vmxnet3_TxDataDesc));
+			else
+				gdesc->txd.addr = RTE_MBUF_DATA_DMA_ADDR(m_seg);
+
 			gdesc->dword[2] = dw2 | m_seg->data_len;
 			gdesc->dword[3] = 0;
 
-- 
1.9.1