[PATCH] net/iavf: remove extra copy step in Rx bulk path

[Kathleen Capella]

The failure in ci/iol-broadcom-Functional on this patch seems to be unrelated to the patch.

> -----Original Message-----
> From: Kathleen Capella <kathleen.capella at arm.com>
> Sent: Thursday, March 24, 2022 5:12 PM
> To: Jingjing Wu <jingjing.wu at intel.com>; Beilei Xing <beilei.xing at intel.com>
> Cc: dev at dpdk.org; nd <nd at arm.com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli at arm.com>; Dharmik Thakkar
> <Dharmik.Thakkar at arm.com>; Kathleen Capella
> <Kathleen.Capella at arm.com>
> Subject: [PATCH] net/iavf: remove extra copy step in Rx bulk path
> 
> In the Rx bulk path, packets which are taken from the HW ring, are first
> copied to the stage data structure and then later copied from the stage to the
> rx_pkts array. For the number of packets requested immediately by the
> receiving function, this two-step process adds extra overhead that is not
> necessary.
> 
> Instead, put requested number of packets directly into the rx_pkts array and
> only stage excess packets. On N1SDP with 1 core/port, l3fwd saw up to 4%
> performance improvement. On x86, no difference in performance was
> observed.
> 
> Signed-off-by: Kathleen Capella <kathleen.capella at arm.com>
> Suggested-by: Dharmik Thakkar <dharmik.thakkar at arm.com>
> ---
>  drivers/net/iavf/iavf_rxtx.c | 74 ++++++++++++++++++++++++------------
>  1 file changed, 49 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/net/iavf/iavf_rxtx.c b/drivers/net/iavf/iavf_rxtx.c index
> 16e8d021f9..245dd225fd 100644
> --- a/drivers/net/iavf/iavf_rxtx.c
> +++ b/drivers/net/iavf/iavf_rxtx.c
> @@ -1813,7 +1813,9 @@ iavf_recv_scattered_pkts(void *rx_queue, struct
> rte_mbuf **rx_pkts,
> 
>  #define IAVF_LOOK_AHEAD 8
>  static inline int
> -iavf_rx_scan_hw_ring_flex_rxd(struct iavf_rx_queue *rxq)
> +iavf_rx_scan_hw_ring_flex_rxd(struct iavf_rx_queue *rxq,
> +			    struct rte_mbuf **rx_pkts,
> +			    uint16_t nb_pkts)
>  {
>  	volatile union iavf_rx_flex_desc *rxdp;
>  	struct rte_mbuf **rxep;
> @@ -1822,6 +1824,7 @@ iavf_rx_scan_hw_ring_flex_rxd(struct
> iavf_rx_queue *rxq)
>  	uint16_t pkt_len;
>  	int32_t s[IAVF_LOOK_AHEAD], var, nb_dd;
>  	int32_t i, j, nb_rx = 0;
> +	int32_t nb_staged = 0;
>  	uint64_t pkt_flags;
>  	const uint32_t *ptype_tbl = rxq->vsi->adapter->ptype_tbl;
> 
> @@ -1867,8 +1870,6 @@ iavf_rx_scan_hw_ring_flex_rxd(struct
> iavf_rx_queue *rxq)  #endif
>  		}
> 
> -		nb_rx += nb_dd;
> -
>  		/* Translate descriptor info to mbuf parameters */
>  		for (j = 0; j < nb_dd; j++) {
>  			IAVF_DUMP_RX_DESC(rxq, &rxdp[j],
> @@ -1892,24 +1893,34 @@ iavf_rx_scan_hw_ring_flex_rxd(struct
> iavf_rx_queue *rxq)
>  			pkt_flags =
> iavf_flex_rxd_error_to_pkt_flags(stat_err0);
> 
>  			mb->ol_flags |= pkt_flags;
> -		}
> 
> -		for (j = 0; j < IAVF_LOOK_AHEAD; j++)
> -			rxq->rx_stage[i + j] = rxep[j];
> +			/* Put up to nb_pkts directly into buffers */
> +			if ((i + j) < nb_pkts) {
> +				rx_pkts[i + j] = rxep[j];
> +				nb_rx++;
> +			} else {
> +				/* Stage excess pkts received */
> +				rxq->rx_stage[nb_staged] = rxep[j];
> +				nb_staged++;
> +			}
> +		}
> 
>  		if (nb_dd != IAVF_LOOK_AHEAD)
>  			break;
>  	}
> 
> +	/* Update rxq->rx_nb_avail to reflect number of staged pkts */
> +	rxq->rx_nb_avail = nb_staged;
> +
>  	/* Clear software ring entries */
> -	for (i = 0; i < nb_rx; i++)
> +	for (i = 0; i < (nb_rx + nb_staged); i++)
>  		rxq->sw_ring[rxq->rx_tail + i] = NULL;
> 
>  	return nb_rx;
>  }
> 
>  static inline int
> -iavf_rx_scan_hw_ring(struct iavf_rx_queue *rxq)
> +iavf_rx_scan_hw_ring(struct iavf_rx_queue *rxq, struct rte_mbuf
> +**rx_pkts, uint16_t nb_pkts)
>  {
>  	volatile union iavf_rx_desc *rxdp;
>  	struct rte_mbuf **rxep;
> @@ -1919,6 +1930,7 @@ iavf_rx_scan_hw_ring(struct iavf_rx_queue *rxq)
>  	uint32_t rx_status;
>  	int32_t s[IAVF_LOOK_AHEAD], var, nb_dd;
>  	int32_t i, j, nb_rx = 0;
> +	int32_t nb_staged = 0;
>  	uint64_t pkt_flags;
>  	const uint32_t *ptype_tbl = rxq->vsi->adapter->ptype_tbl;
> 
> @@ -1970,8 +1982,6 @@ iavf_rx_scan_hw_ring(struct iavf_rx_queue *rxq)
> #endif
>  		}
> 
> -		nb_rx += nb_dd;
> -
>  		/* Translate descriptor info to mbuf parameters */
>  		for (j = 0; j < nb_dd; j++) {
>  			IAVF_DUMP_RX_DESC(rxq, &rxdp[j],
> @@ -2000,17 +2010,26 @@ iavf_rx_scan_hw_ring(struct iavf_rx_queue
> *rxq)
>  				pkt_flags |= iavf_rxd_build_fdir(&rxdp[j],
> mb);
> 
>  			mb->ol_flags |= pkt_flags;
> -		}
> 
> -		for (j = 0; j < IAVF_LOOK_AHEAD; j++)
> -			rxq->rx_stage[i + j] = rxep[j];
> +			/* Put up to nb_pkts directly into buffers */
> +			if ((i + j) < nb_pkts) {
> +				rx_pkts[i + j] = rxep[j];
> +				nb_rx++;
> +			} else { /* Stage excess pkts received */
> +				rxq->rx_stage[nb_staged] = rxep[j];
> +				nb_staged++;
> +			}
> +		}
> 
>  		if (nb_dd != IAVF_LOOK_AHEAD)
>  			break;
>  	}
> 
> +	/* Update rxq->rx_nb_avail to reflect number of staged pkts */
> +	rxq->rx_nb_avail = nb_staged;
> +
>  	/* Clear software ring entries */
> -	for (i = 0; i < nb_rx; i++)
> +	for (i = 0; i < (nb_rx + nb_staged); i++)
>  		rxq->sw_ring[rxq->rx_tail + i] = NULL;
> 
>  	return nb_rx;
> @@ -2098,23 +2117,31 @@ rx_recv_pkts(void *rx_queue, struct rte_mbuf
> **rx_pkts, uint16_t nb_pkts)
>  		return iavf_rx_fill_from_stage(rxq, rx_pkts, nb_pkts);
> 
>  	if (rxq->rxdid >= IAVF_RXDID_FLEX_NIC && rxq->rxdid <=
> IAVF_RXDID_LAST)
> -		nb_rx = (uint16_t)iavf_rx_scan_hw_ring_flex_rxd(rxq);
> +		nb_rx = (uint16_t)iavf_rx_scan_hw_ring_flex_rxd(rxq,
> rx_pkts,
> +nb_pkts);
>  	else
> -		nb_rx = (uint16_t)iavf_rx_scan_hw_ring(rxq);
> +		nb_rx = (uint16_t)iavf_rx_scan_hw_ring(rxq, rx_pkts,
> nb_pkts);
> +
>  	rxq->rx_next_avail = 0;
> -	rxq->rx_nb_avail = nb_rx;
> -	rxq->rx_tail = (uint16_t)(rxq->rx_tail + nb_rx);
> +	rxq->rx_tail = (uint16_t)(rxq->rx_tail + nb_rx + rxq->rx_nb_avail);
> 
>  	if (rxq->rx_tail > rxq->rx_free_trigger) {
>  		if (iavf_rx_alloc_bufs(rxq) != 0) {
> -			uint16_t i, j;
> +			uint16_t i, j, nb_staged;
> 
>  			/* TODO: count rx_mbuf_alloc_failed here */
> 
> +			nb_staged = rxq->rx_nb_avail;
>  			rxq->rx_nb_avail = 0;
> -			rxq->rx_tail = (uint16_t)(rxq->rx_tail - nb_rx);
> -			for (i = 0, j = rxq->rx_tail; i < nb_rx; i++, j++)
> +
> +			rxq->rx_tail = (uint16_t)(rxq->rx_tail - (nb_rx +
> nb_staged));
> +			for (i = 0, j = rxq->rx_tail; i < nb_rx; i++, j++) {
> +				rxq->sw_ring[j] = rx_pkts[i];
> +				rx_pkts[i] = NULL;
> +			}
> +			for (i = 0, j = rxq->rx_tail + nb_rx; i < nb_staged; i++,
> j++) {
>  				rxq->sw_ring[j] = rxq->rx_stage[i];
> +				rx_pkts[i] = NULL;
> +			}
> 
>  			return 0;
>  		}
> @@ -2127,10 +2154,7 @@ rx_recv_pkts(void *rx_queue, struct rte_mbuf
> **rx_pkts, uint16_t nb_pkts)
>  		   rxq->port_id, rxq->queue_id,
>  		   rxq->rx_tail, nb_rx);
> 
> -	if (rxq->rx_nb_avail)
> -		return iavf_rx_fill_from_stage(rxq, rx_pkts, nb_pkts);
> -
> -	return 0;
> +	return nb_rx;
>  }
> 
>  static uint16_t
> --
> 2.31.1