Re: [PATCH v3] ixgbe: remove vector pmd burst size restriction

On receive side, the burst size now floor aligns to RTE_IXGBE_DESCS_PER_LOOP power of 2.
According to this rule, the burst size less than 4 still won't receive anything.
(Before this change, the burst size less than 32 can't receive anything.)
_recv_*_pkts_vec returns no more than 32(RTE_IXGBE_RXQ_REARM_THRESH) packets.

On transmit side, the max burst size no longer bind with a constant, however it still
require to check the cross tx_rs_thresh violation.

There's no obvious performance drop found on both recv_pkts_vec
and recv_scattered_pkts_vec on burst size 32.

Signed-off-by: Cunming Liang <redacted>
---
  v3 change:
   - reword the init print log

  v2 change:
   - keep max rx burst size in 32
   - reword some comments

  drivers/net/ixgbe/ixgbe_rxtx.c     |  4 +++-
  drivers/net/ixgbe/ixgbe_rxtx.h     |  5 ++---
  drivers/net/ixgbe/ixgbe_rxtx_vec.c | 39 +++++++++++++++++++++-----------------
  3 files changed, 27 insertions(+), 21 deletions(-)

diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
index 91023b9..03eb45d 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx.c

@@ -4008,7 +4008,9 @@ ixgbe_set_rx_function(struct rte_eth_dev *dev)
  	 */
  	} else if (adapter->rx_vec_allowed) {
  		PMD_INIT_LOG(DEBUG, "Vector rx enabled, please make sure RX "
-				   "burst size no less than 32.");
+				    "burst size no less than %d (port=%d).",
+			     RTE_IXGBE_DESCS_PER_LOOP,
+			     dev->data->port_id);

  		dev->rx_pkt_burst = ixgbe_recv_pkts_vec;
  	} else if (adapter->rx_bulk_alloc_allowed) {

diff --git a/drivers/net/ixgbe/ixgbe_rxtx.h b/drivers/net/ixgbe/ixgbe_rxtx.h
index 113682a..b9eca67 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx.h
+++ b/drivers/net/ixgbe/ixgbe_rxtx.h

@@ -47,9 +47,8 @@
  	(uint64_t) ((mb)->buf_physaddr + RTE_PKTMBUF_HEADROOM)

  #ifdef RTE_IXGBE_INC_VECTOR
-#define RTE_IXGBE_VPMD_RX_BURST         32
-#define RTE_IXGBE_VPMD_TX_BURST         32
-#define RTE_IXGBE_RXQ_REARM_THRESH      RTE_IXGBE_VPMD_RX_BURST
+#define RTE_IXGBE_RXQ_REARM_THRESH      32
+#define RTE_IXGBE_MAX_RX_BURST          RTE_IXGBE_RXQ_REARM_THRESH
  #define RTE_IXGBE_TX_MAX_FREE_BUF_SZ    64
  #endif

diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec.c b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
index cf25a53..2ca0e4c 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx_vec.c

@@ -245,13 +245,13 @@ desc_to_olflags_v(__m128i descs[4], struct rte_mbuf **rx_pkts)
  #endif

  /*
- * vPMD receive routine, now only accept (nb_pkts == RTE_IXGBE_VPMD_RX_BURST)
- * in one loop
+ * vPMD raw receive routine, only accept(nb_pkts >= RTE_IXGBE_DESCS_PER_LOOP)
   *
   * Notice:
- * - nb_pkts < RTE_IXGBE_VPMD_RX_BURST, just return no packet
- * - nb_pkts > RTE_IXGBE_VPMD_RX_BURST, only scan RTE_IXGBE_VPMD_RX_BURST
+ * - nb_pkts < RTE_IXGBE_DESCS_PER_LOOP, just return no packet
+ * - nb_pkts > RTE_IXGBE_MAX_RX_BURST, only scan RTE_IXGBE_MAX_RX_BURST
   *   numbers of DD bit
+ * - floor align nb_pkts to a RTE_IXGBE_DESC_PER_LOOP power-of-two
   * - don't support ol_flags for rss and csum err
   */
  static inline uint16_t

@@ -286,8 +286,11 @@ _recv_raw_pkts_vec(struct ixgbe_rx_queue *rxq, struct rte_mbuf **rx_pkts,
  	__m128i dd_check, eop_check;
  #endif /* RTE_NEXT_ABI */

-	if (unlikely(nb_pkts < RTE_IXGBE_VPMD_RX_BURST))
-		return 0;
+	/* nb_pkts shall be less equal than RTE_IXGBE_MAX_RX_BURST */
+	nb_pkts = RTE_MIN(nb_pkts, RTE_IXGBE_MAX_RX_BURST);
+
+	/* nb_pkts has to be floor-aligned to RTE_IXGBE_DESCS_PER_LOOP */
+	nb_pkts = RTE_ALIGN_FLOOR(nb_pkts, RTE_IXGBE_DESCS_PER_LOOP);

  	/* Just the act of getting into the function from the application is
  	 * going to cost about 7 cycles */

@@ -356,7 +359,7 @@ _recv_raw_pkts_vec(struct ixgbe_rx_queue *rxq, struct rte_mbuf **rx_pkts,
  	 * D. fill info. from desc to mbuf
  	 */
  #endif /* RTE_NEXT_ABI */
-	for (pos = 0, nb_pkts_recd = 0; pos < RTE_IXGBE_VPMD_RX_BURST;
+	for (pos = 0, nb_pkts_recd = 0; pos < nb_pkts;
  			pos += RTE_IXGBE_DESCS_PER_LOOP,
  			rxdp += RTE_IXGBE_DESCS_PER_LOOP) {
  #ifdef RTE_NEXT_ABI

@@ -518,13 +521,13 @@ _recv_raw_pkts_vec(struct ixgbe_rx_queue *rxq, struct rte_mbuf **rx_pkts,
  }

  /*
- * vPMD receive routine, now only accept (nb_pkts == RTE_IXGBE_VPMD_RX_BURST)
- * in one loop
+ * vPMD receive routine, only accept(nb_pkts >= RTE_IXGBE_DESCS_PER_LOOP)
   *
   * Notice:
- * - nb_pkts < RTE_IXGBE_VPMD_RX_BURST, just return no packet
- * - nb_pkts > RTE_IXGBE_VPMD_RX_BURST, only scan RTE_IXGBE_VPMD_RX_BURST
+ * - nb_pkts < RTE_IXGBE_DESCS_PER_LOOP, just return no packet
+ * - nb_pkts > RTE_IXGBE_MAX_RX_BURST, only scan RTE_IXGBE_MAX_RX_BURST
   *   numbers of DD bit
+ * - floor align nb_pkts to a RTE_IXGBE_DESC_PER_LOOP power-of-two
   * - don't support ol_flags for rss and csum err
   */
  uint16_t

@@ -538,12 +541,11 @@ static inline uint16_t
  reassemble_packets(struct ixgbe_rx_queue *rxq, struct rte_mbuf **rx_bufs,
  		uint16_t nb_bufs, uint8_t *split_flags)
  {
-	struct rte_mbuf *pkts[RTE_IXGBE_VPMD_RX_BURST]; /*finished pkts*/
+	struct rte_mbuf *pkts[nb_bufs]; /*finished pkts*/
  	struct rte_mbuf *start = rxq->pkt_first_seg;
  	struct rte_mbuf *end =  rxq->pkt_last_seg;
  	unsigned pkt_idx, buf_idx;

-
  	for (buf_idx = 0, pkt_idx = 0; buf_idx < nb_bufs; buf_idx++) {
  		if (end != NULL) {
  			/* processing a split packet */

@@ -603,14 +605,17 @@ reassemble_packets(struct ixgbe_rx_queue *rxq, struct rte_mbuf **rx_bufs,
   *
   * Notice:
   * - don't support ol_flags for rss and csum err
- * - now only accept (nb_pkts == RTE_IXGBE_VPMD_RX_BURST)
+ * - nb_pkts < RTE_IXGBE_DESCS_PER_LOOP, just return no packet
+ * - nb_pkts > RTE_IXGBE_MAX_RX_BURST, only scan RTE_IXGBE_MAX_RX_BURST
+ *   numbers of DD bit
+ * - floor align nb_pkts to a RTE_IXGBE_DESC_PER_LOOP power-of-two
   */
  uint16_t
  ixgbe_recv_scattered_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
  		uint16_t nb_pkts)
  {
  	struct ixgbe_rx_queue *rxq = rx_queue;
-	uint8_t split_flags[RTE_IXGBE_VPMD_RX_BURST] = {0};
+	uint8_t split_flags[RTE_IXGBE_MAX_RX_BURST] = {0};

  	/* get some new buffers */
  	uint16_t nb_bufs = _recv_raw_pkts_vec(rxq, rx_pkts, nb_pkts,

@@ -735,8 +740,8 @@ ixgbe_xmit_pkts_vec(void *tx_queue, struct rte_mbuf **tx_pkts,
  	uint64_t rs = IXGBE_ADVTXD_DCMD_RS|DCMD_DTYP_FLAGS;
  	int i;

-	if (unlikely(nb_pkts > RTE_IXGBE_VPMD_TX_BURST))
-		nb_pkts = RTE_IXGBE_VPMD_TX_BURST;
+	/* cross rx_thresh boundary is not allowed */
+	nb_pkts = RTE_MIN(nb_pkts, txq->tx_rs_thresh);

  	if (txq->nb_tx_free < txq->tx_free_thresh)
  		ixgbe_tx_free_bufs(txq);