[dpdk-dev] [PATCH 2/2] net/mlx5: reduce unnecessary memory access

Slava Ovsiienko viacheslavo at nvidia.com
Fri Jul 2 09:05:57 CEST 2021


Hi, Ruifeng

Could we go further and implement loop inside the conditional?
Like this:
if (mlx5_mr_btree_len(&rxq->mr_ctrl.cache_bh) > 1) {
	for (i = 0; i < n; ++i) {
		void *buf_addr = elts[i]->buf_addr;

		wq[i].addr = rte_cpu_to_be_64((uintptr_t)buf_addr +
					      RTE_PKTMBUF_HEADROOM);
		wq[i].lkey = mlx5_rx_mb2mr(rxq, elts[i]);
	}
} else {
	for (i = 0; i < n; ++i) {
		void *buf_addr = elts[i]->buf_addr;

		wq[i].addr = rte_cpu_to_be_64((uintptr_t)buf_addr +
					      RTE_PKTMBUF_HEADROOM);
	}
}
What do you think?
Also,  we should check the performance on other archs is not affected.

With best regards,
Slava

> -----Original Message-----
> From: Ruifeng Wang <ruifeng.wang at arm.com>
> Sent: Tuesday, June 1, 2021 11:31
> To: Raslan Darawsheh <rasland at nvidia.com>; Matan Azrad
> <matan at nvidia.com>; Shahaf Shuler <shahafs at nvidia.com>; Slava Ovsiienko
> <viacheslavo at nvidia.com>
> Cc: dev at dpdk.org; jerinj at marvell.com; nd at arm.com;
> honnappa.nagarahalli at arm.com; Ruifeng Wang <ruifeng.wang at arm.com>
> Subject: [PATCH 2/2] net/mlx5: reduce unnecessary memory access
> 
> MR btree len is a constant during Rx replenish.
> Moved retrieve of the value out of loop to reduce data loads.
> Slight performance uplift was measured on N1SDP.
> 
> Signed-off-by: Ruifeng Wang <ruifeng.wang at arm.com>
> ---
>  drivers/net/mlx5/mlx5_rxtx_vec.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/mlx5/mlx5_rxtx_vec.c
> b/drivers/net/mlx5/mlx5_rxtx_vec.c
> index d5af2d91ff..fc7e2a7f41 100644
> --- a/drivers/net/mlx5/mlx5_rxtx_vec.c
> +++ b/drivers/net/mlx5/mlx5_rxtx_vec.c
> @@ -95,6 +95,7 @@ mlx5_rx_replenish_bulk_mbuf(struct mlx5_rxq_data
> *rxq)
>  	volatile struct mlx5_wqe_data_seg *wq =
>  		&((volatile struct mlx5_wqe_data_seg *)rxq->wqes)[elts_idx];
>  	unsigned int i;
> +	uint16_t btree_len;
> 
>  	if (n >= rxq->rq_repl_thresh) {
>  		MLX5_ASSERT(n >=
> MLX5_VPMD_RXQ_RPLNSH_THRESH(q_n));
> @@ -106,6 +107,8 @@ mlx5_rx_replenish_bulk_mbuf(struct mlx5_rxq_data
> *rxq)
>  			rxq->stats.rx_nombuf += n;
>  			return;
>  		}
> +
> +		btree_len = mlx5_mr_btree_len(&rxq->mr_ctrl.cache_bh);
>  		for (i = 0; i < n; ++i) {
>  			void *buf_addr;
> 
> @@ -119,8 +122,7 @@ mlx5_rx_replenish_bulk_mbuf(struct mlx5_rxq_data
> *rxq)
>  			wq[i].addr = rte_cpu_to_be_64((uintptr_t)buf_addr +
> 
> RTE_PKTMBUF_HEADROOM);
>  			/* If there's a single MR, no need to replace LKey. */
> -			if (unlikely(mlx5_mr_btree_len(&rxq-
> >mr_ctrl.cache_bh)
> -				     > 1))
> +			if (unlikely(btree_len > 1))
>  				wq[i].lkey = mlx5_rx_mb2mr(rxq, elts[i]);
>  		}
>  		rxq->rq_ci += n;
> --
> 2.25.1



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