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

[Ruifeng Wang <Ruifeng.Wang@arm.com>]

> -----Original Message-----
> From: Slava Ovsiienko <viacheslavo@nvidia.com>
> Sent: Friday, July 2, 2021 3:06 PM
> To: Ruifeng Wang <Ruifeng.Wang@arm.com>; Raslan Darawsheh
> <rasland@nvidia.com>; Matan Azrad <matan@nvidia.com>; Shahaf Shuler
> <shahafs@nvidia.com>
> Cc: dev@dpdk.org; jerinj@marvell.com; nd <nd@arm.com>; Honnappa
> Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Subject: RE: [PATCH 2/2] net/mlx5: reduce unnecessary memory access
> 
> 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?
Agree. Loop inside the conditional should be more efficient.

> Also,  we should check the performance on other archs is not affected.
I will also test on x86 platform that I have.

> 
> With best regards,
> Slava
> 
> > -----Original Message-----
> > From: Ruifeng Wang <ruifeng.wang@arm.com>
> > Sent: Tuesday, June 1, 2021 11:31
> > To: Raslan Darawsheh <rasland@nvidia.com>; Matan Azrad
> > <matan@nvidia.com>; Shahaf Shuler <shahafs@nvidia.com>; Slava
> > Ovsiienko <viacheslavo@nvidia.com>
> > Cc: dev@dpdk.org; jerinj@marvell.com; nd@arm.com;
> > honnappa.nagarahalli@arm.com; Ruifeng Wang <ruifeng.wang@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@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