netdev - Re: [PATCH][net-next] net/mlx5e: avoid to call net_dim and dim_update

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Message-ID: <7afa4b93-59da-4063-9a4b-6f958555d4b3@intel.com>
Date: Mon, 16 Dec 2024 06:09:21 +0100
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Li RongQing <lirongqing@...du.com>, Shuo Li <lishuo02@...du.com>,
	<saeedm@...dia.com>
CC: <tariqt@...dia.com>, <leon@...nel.org>, <netdev@...r.kernel.org>,
	<pabeni@...hat.com>, <kuba@...nel.org>, <edumazet@...gle.com>,
	<davem@...emloft.net>, <andrew+netdev@...n.ch>
Subject: Re: [PATCH][net-next] net/mlx5e: avoid to call net_dim and
 dim_update_sample

On 12/12/24 12:47, Li RongQing wrote:
> High cpu usage for net_dim is seen still after commit 61bf0009a765

CPU

> ("dim: pass dim_sample to net_dim() by reference"), the calling
> net_dim can be avoid under network low throughput or pingpong mode by
> checking the event counter, even under high throughput, it maybe only

s/maybe/may be/

> rx or tx direction

Rx, Tx

> 
> And don't initialize dim_sample variable, since it will gets
> overwritten by dim_update_sample

Good point.

> 
> Signed-off-by: Li RongQing <lirongqing@...du.com>
> Signed-off-by: Shuo Li <lishuo02@...du.com>
> ---
>   drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c | 20 ++++++++++++++++++--
>   1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
> index 7610829..7c525e9 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
> @@ -49,11 +49,19 @@ static inline bool mlx5e_channel_no_affinity_change(struct mlx5e_channel *c)
>   static void mlx5e_handle_tx_dim(struct mlx5e_txqsq *sq)
>   {
>   	struct mlx5e_sq_stats *stats = sq->stats;
> -	struct dim_sample dim_sample = {};
> +	struct dim_sample dim_sample;
> +	u16 nevents;
>   
>   	if (unlikely(!test_bit(MLX5E_SQ_STATE_DIM, &sq->state)))
>   		return;
>   
> +	if (sq->dim->state == DIM_MEASURE_IN_PROGRESS) {
> +		nevents = BIT_GAP(BITS_PER_TYPE(u16), sq->cq.event_ctr,
> +						  sq->dim->start_sample.event_ctr);

indentation is off

> +		if (nevents < DIM_NEVENTS)
> +			return;

this very piece of code is present in net_dim()...

> +	}
> +
>   	dim_update_sample(sq->cq.event_ctr, stats->packets, stats->bytes, &dim_sample);
>   	net_dim(sq->dim, &dim_sample);
>   }
> @@ -61,11 +69,19 @@ static void mlx5e_handle_tx_dim(struct mlx5e_txqsq *sq)
>   static void mlx5e_handle_rx_dim(struct mlx5e_rq *rq)
>   {
>   	struct mlx5e_rq_stats *stats = rq->stats;
> -	struct dim_sample dim_sample = {};
> +	struct dim_sample dim_sample;
> +	u16 nevents;
>   
>   	if (unlikely(!test_bit(MLX5E_RQ_STATE_DIM, &rq->state)))
>   		return;
>   
> +	if (rq->dim->state == DIM_MEASURE_IN_PROGRESS) {
> +		nevents = BIT_GAP(BITS_PER_TYPE(u16), rq->cq.event_ctr,
> +						  rq->dim->start_sample.event_ctr);
> +		if (nevents < DIM_NEVENTS)
> +			return;
> +	}

and you have copied it twice only to avoid ktime_get() call?

> +
>   	dim_update_sample(rq->cq.event_ctr, stats->packets, stats->bytes, &dim_sample);
>   	net_dim(rq->dim, &dim_sample);
>   }