[dpdk-dev] [PATCH RFC 2/2] net/ixgbe: allow bulk alloc for the max size desc ring

[Ilya Maximets <i.maximets@samsung.com>]

The only reason why bulk alloc disabled for the rings with
more than (IXGBE_MAX_RING_DESC - RTE_PMD_IXGBE_RX_MAX_BURST)
descriptors is the possible out-of-bound access to the dma
memory. But it's the artificial limit and can be easily
avoided by allocating of RTE_PMD_IXGBE_RX_MAX_BURST more
descriptors in memory. This will not interfere the HW and,
as soon as all rings' memory zeroized, Rx functions will
work correctly.

This change allows to use vectorized Rx functions with
4096 descriptors in Rx ring which is important to achieve
zero packet drop rate in high-load installations.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
---
 drivers/net/ixgbe/ixgbe_rxtx.c | 17 +----------------
 drivers/net/ixgbe/ixgbe_rxtx.h |  2 +-
 2 files changed, 2 insertions(+), 17 deletions(-)

diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
index 2ce8234..07c04c3 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx.c
@@ -2585,7 +2585,6 @@ check_rx_burst_bulk_alloc_preconditions(struct ixgbe_rx_queue *rxq)
 	 *   rxq->rx_free_thresh >= RTE_PMD_IXGBE_RX_MAX_BURST
 	 *   rxq->rx_free_thresh < rxq->nb_rx_desc
 	 *   (rxq->nb_rx_desc % rxq->rx_free_thresh) == 0
-	 *   rxq->nb_rx_desc<(IXGBE_MAX_RING_DESC-RTE_PMD_IXGBE_RX_MAX_BURST)
 	 * Scattered packets are not supported.  This should be checked
 	 * outside of this function.
 	 */
@@ -2607,15 +2606,6 @@ check_rx_burst_bulk_alloc_preconditions(struct ixgbe_rx_queue *rxq)
 			     "rxq->rx_free_thresh=%d",
 			     rxq->nb_rx_desc, rxq->rx_free_thresh);
 		ret = -EINVAL;
-	} else if (!(rxq->nb_rx_desc <
-	       (IXGBE_MAX_RING_DESC - RTE_PMD_IXGBE_RX_MAX_BURST))) {
-		PMD_INIT_LOG(DEBUG, "Rx Burst Bulk Alloc Preconditions: "
-			     "rxq->nb_rx_desc=%d, "
-			     "IXGBE_MAX_RING_DESC=%d, "
-			     "RTE_PMD_IXGBE_RX_MAX_BURST=%d",
-			     rxq->nb_rx_desc, IXGBE_MAX_RING_DESC,
-			     RTE_PMD_IXGBE_RX_MAX_BURST);
-		ret = -EINVAL;
 	}
 
 	return ret;
@@ -2632,12 +2622,7 @@ ixgbe_reset_rx_queue(struct ixgbe_adapter *adapter, struct ixgbe_rx_queue *rxq)
 	/*
 	 * By default, the Rx queue setup function allocates enough memory for
 	 * IXGBE_MAX_RING_DESC.  The Rx Burst bulk allocation function requires
-	 * extra memory at the end of the descriptor ring to be zero'd out. A
-	 * pre-condition for using the Rx burst bulk alloc function is that the
-	 * number of descriptors is less than or equal to
-	 * (IXGBE_MAX_RING_DESC - RTE_PMD_IXGBE_RX_MAX_BURST). Check all the
-	 * constraints here to see if we need to zero out memory after the end
-	 * of the H/W descriptor ring.
+	 * extra memory at the end of the descriptor ring to be zero'd out.
 	 */
 	if (adapter->rx_bulk_alloc_allowed)
 		/* zero out extra memory */
diff --git a/drivers/net/ixgbe/ixgbe_rxtx.h b/drivers/net/ixgbe/ixgbe_rxtx.h
index 2608b36..1abc6f2 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx.h
+++ b/drivers/net/ixgbe/ixgbe_rxtx.h
@@ -67,7 +67,7 @@
 #define RTE_IXGBE_MAX_RX_BURST          RTE_IXGBE_RXQ_REARM_THRESH
 #endif
 
-#define RX_RING_SZ ((IXGBE_MAX_RING_DESC + RTE_IXGBE_DESCS_PER_LOOP - 1) * \
+#define RX_RING_SZ ((IXGBE_MAX_RING_DESC + RTE_PMD_IXGBE_RX_MAX_BURST) * \
 		    sizeof(union ixgbe_adv_rx_desc))
 
 #ifdef RTE_PMD_PACKET_PREFETCH
-- 
2.7.4