[dpdk-dev] [PATCH] Add missing prefetches to i40e bulk rx path

[Vladyslav Buslov]

Hello,

Recently I tried to use bulk rx function to reduce CPU usage of rte_eth_rx_burst.
However application performance with i40e_recv_pkts_bulk_alloc was significantly worse than with i40e_recv_pkts. (3m less PPS, 0.5 IPC on receiving core)

Quick investigation revealed two problems:
 - First payload cacheline is prefetched in i40e_recv_pkts but not in i40e_recv_pkts_bulk_alloc.
 - Only first line of next mbuf is prefetched during mbuf init in i40e_rx_alloc_bufs. This causes cache miss at setting 'next' field from mbuf cacheline1 to NULL.

Fixing these two small issues significantly reduced CPU time spent in rte_eth_rx_burst and improved PPS compared to both original i40e_recv_pkts_bulk_alloc and i40e_recv_pkts.

Regards,

Vladyslav Buslov (1):
  net/i40e: add additional prefetch instructions for bulk rx

 drivers/net/i40e/i40e_rxtx.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

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2.8.3