[dpdk-dev] [PATCH 2/2] ixgbe:replace compiler memory barrier and rte_wmb with rte_dma_rmb and rte_dma_wmb.

[WangDong <dong.wang.pro@hotmail.com>]

---
 drivers/net/ixgbe/ixgbe_rxtx.c     | 30 +++++++++---------------------
 drivers/net/ixgbe/ixgbe_rxtx_vec.c |  3 +++
 2 files changed, 12 insertions(+), 21 deletions(-)

diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
index 3ace8a8..3316488 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx.c
@@ -130,6 +130,7 @@ ixgbe_tx_free_bufs(struct ixgbe_tx_queue *txq)
 
 	/* check DD bit on threshold descriptor */
 	status = txq->tx_ring[txq->tx_next_dd].wb.status;
+	rte_dma_rmb();
 	if (! (status & IXGBE_ADVTXD_STAT_DD))
 		return 0;
 
@@ -320,7 +321,7 @@ tx_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 		txq->tx_tail = 0;
 
 	/* update tail pointer */
-	rte_wmb();
+	rte_dma_wmb();
 	IXGBE_PCI_REG_WRITE(txq->tdt_reg_addr, txq->tx_tail);
 
 	return nb_pkts;
@@ -841,7 +842,6 @@ ixgbe_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 		txd->read.cmd_type_len |= rte_cpu_to_le_32(cmd_type_len);
 	}
 end_of_tx:
-	rte_wmb();
 
 	/*
 	 * Set the Transmit Descriptor Tail (TDT)
@@ -849,6 +849,7 @@ end_of_tx:
 	PMD_TX_LOG(DEBUG, "port_id=%u queue_id=%u tx_tail=%u nb_tx=%u",
 		   (unsigned) txq->port_id, (unsigned) txq->queue_id,
 		   (unsigned) tx_id, (unsigned) nb_tx);
+	rte_dma_wmb();
 	IXGBE_PCI_REG_WRITE(txq->tdt_reg_addr, tx_id);
 	txq->tx_tail = tx_id;
 
@@ -975,6 +976,7 @@ ixgbe_rx_scan_hw_ring(struct ixgbe_rx_queue *rxq)
 
 		/* Compute how many status bits were set */
 		nb_dd = 0;
+		rte_dma_rmb();
 		for (j = 0; j < LOOK_AHEAD; ++j)
 			nb_dd += s[j] & IXGBE_RXDADV_STAT_DD;
 
@@ -1138,7 +1140,7 @@ rx_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
 		}
 
 		/* update tail pointer */
-		rte_wmb();
+		rte_dma_wmb();
 		IXGBE_PCI_REG_WRITE(rxq->rdt_reg_addr, cur_free_trigger);
 	}
 
@@ -1229,13 +1231,10 @@ ixgbe_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
 		/*
 		 * The order of operations here is important as the DD status
 		 * bit must not be read after any other descriptor fields.
-		 * rx_ring and rxdp are pointing to volatile data so the order
-		 * of accesses cannot be reordered by the compiler. If they were
-		 * not volatile, they could be reordered which could lead to
-		 * using invalid descriptor fields when read from rxd.
 		 */
 		rxdp = &rx_ring[rx_id];
 		staterr = rxdp->wb.upper.status_error;
+		rte_dma_rmb();
 		if (! (staterr & rte_cpu_to_le_32(IXGBE_RXDADV_STAT_DD)))
 			break;
 		rxd = *rxdp;
@@ -1373,6 +1372,7 @@ ixgbe_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
 			   (unsigned) nb_rx);
 		rx_id = (uint16_t) ((rx_id == 0) ?
 				     (rxq->nb_rx_desc - 1) : (rx_id - 1));
+		rte_dma_wmb();
 		IXGBE_PCI_REG_WRITE(rxq->rdt_reg_addr, rx_id);
 		nb_hold = 0;
 	}
@@ -1494,17 +1494,6 @@ ixgbe_recv_pkts_lro(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts,
 
 next_desc:
 		/*
-		 * The code in this whole file uses the volatile pointer to
-		 * ensure the read ordering of the status and the rest of the
-		 * descriptor fields (on the compiler level only!!!). This is so
-		 * UGLY - why not to just use the compiler barrier instead? DPDK
-		 * even has the rte_compiler_barrier() for that.
-		 *
-		 * But most importantly this is just wrong because this doesn't
-		 * ensure memory ordering in a general case at all. For
-		 * instance, DPDK is supposed to work on Power CPUs where
-		 * compiler barrier may just not be enough!
-		 *
 		 * I tried to write only this function properly to have a
 		 * starting point (as a part of an LRO/RSC series) but the
 		 * compiler cursed at me when I tried to cast away the
@@ -1519,12 +1508,11 @@ next_desc:
 		 * TODO:
 		 *    - Get rid of "volatile" crap and let the compiler do its
 		 *      job.
-		 *    - Use the proper memory barrier (rte_rmb()) to ensure the
-		 *      memory ordering below.
 		 */
 		rxdp = &rx_ring[rx_id];
 		staterr = rte_le_to_cpu_32(rxdp->wb.upper.status_error);
 
+		rte_dma_rmb();
 		if (!(staterr & IXGBE_RXDADV_STAT_DD))
 			break;
 
@@ -1704,7 +1692,7 @@ next_desc:
 			   "nb_hold=%u nb_rx=%u",
 			   rxq->port_id, rxq->queue_id, rx_id, nb_hold, nb_rx);
 
-		rte_wmb();
+		rte_dma_wmb();
 		IXGBE_PCI_REG_WRITE(rxq->rdt_reg_addr, prev_id);
 		nb_hold = 0;
 	}
diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec.c b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
index abd10f6..af4d779 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
@@ -123,6 +123,7 @@ ixgbe_rxq_rearm(struct ixgbe_rx_queue *rxq)
 			     (rxq->nb_rx_desc - 1) : (rxq->rxrearm_start - 1));
 
 	/* Update the tail pointer on the NIC */
+	rte_dma_wmb();
 	IXGBE_PCI_REG_WRITE(rxq->rdt_reg_addr, rx_id);
 }
 
@@ -528,6 +529,7 @@ ixgbe_tx_free_bufs(struct ixgbe_tx_queue *txq)
 
 	/* check DD bit on threshold descriptor */
 	status = txq->tx_ring[txq->tx_next_dd].wb.status;
+	rte_dma_rmb();
 	if (!(status & IXGBE_ADVTXD_STAT_DD))
 		return 0;
 
@@ -645,6 +647,7 @@ ixgbe_xmit_pkts_vec(void *tx_queue, struct rte_mbuf **tx_pkts,
 
 	txq->tx_tail = tx_id;
 
+	rte_dma_wmb();
 	IXGBE_PCI_REG_WRITE(txq->tdt_reg_addr, txq->tx_tail);
 
 	return nb_pkts;
-- 
2.1.0