-----Original Message-----
From: Honnappa Nagarahalli <redacted>
Sent: Wednesday, June 30, 2021 9:15 AM
To: Joyce Kong <redacted>; beilei.xing@intel.com;
qi.z.zhang@intel.com; Ruifeng Wang [off-list ref];
bruce.richardson@intel.com; helin.zhang@intel.com
Cc: dev@dpdk.org; stable@dpdk.org; nd <redacted>; Honnappa
Nagarahalli [off-list ref]; nd [off-list ref]
Subject: RE: [PATCH v2] net/i40e: add logic of processing continuous DD bits
for Arm

<snip>

quoted

For Arm platforms, reading descs can get re-ordered, then the status
of DD bits will be discontinuous, so add the logic to only process
continuous descs by checking DD bits.

Fixes: 4861cde46116 ("i40e: new poll mode driver")
Cc: stable@dpdk.org

Signed-off-by: Joyce Kong <redacted>
Reviewed-by: Ruifeng Wang <redacted>
---
 drivers/net/i40e/i40e_rxtx.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/net/i40e/i40e_rxtx.c

b/drivers/net/i40e/i40e_rxtx.c index 6c58decec..86e2f083e 100644

--- a/drivers/net/i40e/i40e_rxtx.c
+++ b/drivers/net/i40e/i40e_rxtx.c

@@ -452,7 +452,7 @@ i40e_rx_scan_hw_ring(struct i40e_rx_queue *rxq)
 	uint16_t pkt_len;
 	uint64_t qword1;
 	uint32_t rx_status;
-	int32_t s[I40E_LOOK_AHEAD], nb_dd;
+	int32_t s[I40E_LOOK_AHEAD], var, nb_dd;
 	int32_t i, j, nb_rx = 0;
 	uint64_t pkt_flags;
 	uint32_t *ptype_tbl = rxq->vsi->adapter->ptype_tbl; @@ -482,11
+482,22 @@ i40e_rx_scan_hw_ring(struct i40e_rx_queue *rxq)
 					I40E_RXD_QW1_STATUS_SHIFT;
 		}

-		rte_smp_rmb();
+		/* This barrier is to order loads of different words in the

descriptor */
+		rte_atomic_thread_fence(__ATOMIC_ACQUIRE);

I think this should go into a separate commit as the following change is
unrelated.

Will separate the two changes in v3.

quoted

 		/* Compute how many status bits were set */
-		for (j = 0, nb_dd = 0; j < I40E_LOOK_AHEAD; j++)
-			nb_dd += s[j] & (1 <<
I40E_RX_DESC_STATUS_DD_SHIFT);
+		for (j = 0, nb_dd = 0; j < I40E_LOOK_AHEAD; j++) {
+			var = s[j] & (1 << I40E_RX_DESC_STATUS_DD_SHIFT);
#ifdef
+RTE_ARCH_ARM
+			/* For Arm platforms, only compute continuous
status bits */
+			if (var)
+				nb_dd += 1;
+			else
+				break;
+#else
+			nb_dd += var;
+#endif
+		}

 		nb_rx += nb_dd;

--
2.17.1