Re: [dpdk-dev] [PATCH v3 2/2] net/mlx5: fix instruction hotspot on replenishing Rx buffer

[Shahaf Shuler <shahafs@mellanox.com>]

Thursday, January 10, 2019 8:35 PM, Yongseok Koh:
> Subject: [dpdk-dev] [PATCH v3 2/2] net/mlx5: fix instruction hotspot on
> replenishing Rx buffer
> 
> On replenishing Rx buffers for vectorized Rx, mbuf->buf_addr isn't needed to
> be accessed as it is static and easily calculated from the mbuf address.
> Accessing the mbuf content causes unnecessary load stall and it is worsened on
> ARM.
> 
> Fixes: 545b884b1da3 ("net/mlx5: fix buffer address posting in SSE Rx")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Yongseok Koh <yskoh@mellanox.com>

Acked-by: Shahaf Shuler <shahafs@mellanox.com>

> ---
> 
> v3:
> * rte_mbuf_buf_addr_default() -> rte_mbuf_buf_addr()
> 
> v2:
> * use the newly introduced API - rte_mbuf_buf_addr_default()
> * fix error in assert
> 
>  drivers/net/mlx5/mlx5_rxtx_vec.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/mlx5/mlx5_rxtx_vec.h
> b/drivers/net/mlx5/mlx5_rxtx_vec.h
> index fda7004e2d..989a1fdce5 100644
> --- a/drivers/net/mlx5/mlx5_rxtx_vec.h
> +++ b/drivers/net/mlx5/mlx5_rxtx_vec.h
> @@ -102,8 +102,10 @@ mlx5_rx_replenish_bulk_mbuf(struct mlx5_rxq_data
> *rxq, uint16_t n)
>  		return;
>  	}
>  	for (i = 0; i < n; ++i) {
> -		wq[i].addr = rte_cpu_to_be_64((uintptr_t)elts[i]->buf_addr +
> -					      RTE_PKTMBUF_HEADROOM);
> +		void *buf_addr = rte_mbuf_buf_addr(elts[i], rxq->mp);
> +
> +		assert(buf_addr == elts[i]->buf_addr);
> +		wq[i].addr = rte_cpu_to_be_64((uintptr_t)buf_addr +
> +RTE_PKTMBUF_HEADROOM);
>  		/* If there's only one MR, no need to replace LKey in WQE. */
>  		if (unlikely(mlx5_mr_btree_len(&rxq->mr_ctrl.cache_bh) > 1))
>  			wq[i].lkey = mlx5_rx_mb2mr(rxq, elts[i]);
> --
> 2.11.0