linux-kernel - Re: [PATCH 2/2] net/mlx5e: Leverage sched_numa_hop

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Date:   Wed, 10 Aug 2022 15:57:33 +0300
From:   Tariq Toukan <ttoukan.linux@...il.com>
To:     Valentin Schneider <vschneid@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>
Cc:     Tariq Toukan <tariqt@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...dia.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Gal Pressman <gal@...dia.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH 2/2] net/mlx5e: Leverage sched_numa_hop_mask()



On 8/10/2022 1:51 PM, Valentin Schneider wrote:
> Signed-off-by: Valentin Schneider <vschneid@...hat.com>
> ---
>   drivers/net/ethernet/mellanox/mlx5/core/eq.c | 16 ++++++++++++++--
>   1 file changed, 14 insertions(+), 2 deletions(-)
> 

Missing description.

I had a very detailed description with performance numbers and an 
affinity hints example with before/after tables. I don't want to get 
them lost.


> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/eq.c b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> index 229728c80233..2eb4ffd96a95 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> @@ -809,9 +809,12 @@ static void comp_irqs_release(struct mlx5_core_dev *dev)
>   static int comp_irqs_request(struct mlx5_core_dev *dev)
>   {
>   	struct mlx5_eq_table *table = dev->priv.eq_table;
> +	const struct cpumask *mask;
>   	int ncomp_eqs = table->num_comp_eqs;
> +	int hops = 0;
>   	u16 *cpus;
>   	int ret;
> +	int cpu;
>   	int i;
>   
>   	ncomp_eqs = table->num_comp_eqs;
> @@ -830,8 +833,17 @@ static int comp_irqs_request(struct mlx5_core_dev *dev)
>   		ret = -ENOMEM;
>   		goto free_irqs;
>   	}
> -	for (i = 0; i < ncomp_eqs; i++)
> -		cpus[i] = cpumask_local_spread(i, dev->priv.numa_node);
> +
> +	rcu_read_lock();
> +	for_each_numa_hop_mask(dev->priv.numa_node, hops, mask) {

We don't really use this 'hops' iterator. We always pass 0 (not a 
valuable input...), and we do not care about its final value. Probably 
it's best to hide it from the user into the macro.

> +		for_each_cpu(cpu, mask) {
> +			cpus[i] = cpu;
> +			if (++i == ncomp_eqs)
> +				goto spread_done;
> +		}
> +	}
> +spread_done:
> +	rcu_read_unlock();
>   	ret = mlx5_irqs_request_vectors(dev, cpus, ncomp_eqs, table->comp_irqs);
>   	kfree(cpus);
>   	if (ret < 0)

This logic is typical. Other drivers would also want to use it.
It must be introduced as a service/API function, if not by the sched 
topology, then at least by the networking subsystem.
Jakub, WDYT?