[PATCH 1/2] net/bnxt: avoid unnecessary work in AVX2 Rx path

[PATCH 1/2] net/bnxt: avoid unnecessary work in AVX2 Rx path

[Lance Richardson]

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Each call to the AVX2 vector burst receive function makes at
least one pass through the function's inner loop, loading
256 bytes of completion descriptors and copying 8 rte_mbuf
pointers regardless of whether there are any packets to be
received.

Unidirectional forwarding performance is improved by about
3-4% if we ensure that at least one packet can be received
before entering the inner loop.

Fixes: c4e4c18963b0 ("net/bnxt: add AVX2 RX/Tx")
Cc: stable@dpdk.org
Signed-off-by: Lance Richardson <lance.richardson@broadcom.com>
---
 drivers/net/bnxt/bnxt_rxtx_vec_avx2.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/bnxt/bnxt_rxtx_vec_avx2.c b/drivers/net/bnxt/bnxt_rxtx_vec_avx2.c
index e4905b4fd1..54e3af22ac 100644
--- a/drivers/net/bnxt/bnxt_rxtx_vec_avx2.c
+++ b/drivers/net/bnxt/bnxt_rxtx_vec_avx2.c
@@ -98,6 +98,10 @@ recv_burst_vec_avx2(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts)
 	rte_prefetch0(&cp_desc_ring[cons + 8]);
 	rte_prefetch0(&cp_desc_ring[cons + 12]);
 
+	/* Return immediately if there is not at least one completed packet. */
+	if (!bnxt_cpr_cmp_valid(&cp_desc_ring[cons], raw_cons, cp_ring_size))
+		return 0;
+
 	/* Ensure that we do not go past the ends of the rings. */
 	nb_pkts = RTE_MIN(nb_pkts, RTE_MIN(rx_ring_size - mbcons,
 					   (cp_ring_size - cons) / 2));
-- 
2.25.1


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[PATCH 2/2] net/bnxt: remove software prefetches from AVX2 Rx path

[Lance Richardson]

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Testing has shown no performance benefit from software prefetching
of receive completion descriptors in the AVX2 burst receive path,
and slightly better performance without them on some CPU families,
so this patch removes them.

Fixes: c4e4c18963b0 ("net/bnxt: add AVX2 RX/Tx")
Cc: stable@dpdk.org
Signed-off-by: Lance Richardson <lance.richardson@broadcom.com>
---
 drivers/net/bnxt/bnxt_rxtx_vec_avx2.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/drivers/net/bnxt/bnxt_rxtx_vec_avx2.c b/drivers/net/bnxt/bnxt_rxtx_vec_avx2.c
index 54e3af22ac..34bd22edf0 100644
--- a/drivers/net/bnxt/bnxt_rxtx_vec_avx2.c
+++ b/drivers/net/bnxt/bnxt_rxtx_vec_avx2.c
@@ -92,12 +92,6 @@ recv_burst_vec_avx2(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts)
 	cons = raw_cons & (cp_ring_size - 1);
 	mbcons = (raw_cons / 2) & (rx_ring_size - 1);
 
-	/* Prefetch first four descriptor pairs. */
-	rte_prefetch0(&cp_desc_ring[cons + 0]);
-	rte_prefetch0(&cp_desc_ring[cons + 4]);
-	rte_prefetch0(&cp_desc_ring[cons + 8]);
-	rte_prefetch0(&cp_desc_ring[cons + 12]);
-
 	/* Return immediately if there is not at least one completed packet. */
 	if (!bnxt_cpr_cmp_valid(&cp_desc_ring[cons], raw_cons, cp_ring_size))
 		return 0;
@@ -136,14 +130,6 @@ recv_burst_vec_avx2(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts)
 		_mm256_storeu_si256((void *)&rx_pkts[i + 4], t0);
 #endif
 
-		/* Prefetch eight descriptor pairs for next iteration. */
-		if (i + BNXT_RX_DESCS_PER_LOOP_VEC256 < nb_pkts) {
-			rte_prefetch0(&cp_desc_ring[cons + 16]);
-			rte_prefetch0(&cp_desc_ring[cons + 20]);
-			rte_prefetch0(&cp_desc_ring[cons + 24]);
-			rte_prefetch0(&cp_desc_ring[cons + 28]);
-		}
-
 		/*
 		 * Load eight receive completion descriptors into 256-bit
 		 * registers. Loads are issued in reverse order in order to
-- 
2.25.1


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