netdev - Re: [PATCH net] nfp: use irq_update_affinity

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Message-ID: <ZzGXGEHCPUet3Jqw@LouisNoVo>
Date: Mon, 11 Nov 2024 07:33:12 +0200
From: Louis Peens <louis.peens@...igine.com>
To: Mohammad Heib <mheib@...hat.com>
Cc: netdev@...r.kernel.org, oss-drivers@...igine.com
Subject: Re: [PATCH net] nfp: use irq_update_affinity_hint()

On Thu, Nov 07, 2024 at 01:50:02PM +0200, Mohammad Heib wrote:
> irq_set_affinity_hint() is deprecated, Use irq_update_affinity_hint()
> instead. This removes the side-effect of actually applying the affinity.
> 
> The driver does not really need to worry about spreading its IRQs across
> CPUs. The core code already takes care of that. when the driver applies the
> affinities by itself, it breaks the users' expectations:
> 
> 1. The user configures irqbalance with IRQBALANCE_BANNED_CPULIST in
>    order to prevent IRQs from being moved to certain CPUs that run a
>    real-time workload.
> 
> 2. nfp device reopening will resets the affinity
>    in nfp_net_netdev_open().
> 
> 3. nfp has no idea about irqbalance's config, so it may move an IRQ to
>    a banned CPU. The real-time workload suffers unacceptable latency.
> 
> Signed-off-by: Mohammad Heib <mheib@...hat.com>
> ---
>  drivers/net/ethernet/netronome/nfp/nfp_net_common.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> index 6e0929af0f72..98e098c09c03 100644
> --- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> +++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> @@ -829,7 +829,7 @@ nfp_net_prepare_vector(struct nfp_net *nn, struct nfp_net_r_vector *r_vec,
>  		return err;
>  	}
>  
> -	irq_set_affinity_hint(r_vec->irq_vector, &r_vec->affinity_mask);
> +	irq_update_affinity_hint(r_vec->irq_vector, &r_vec->affinity_mask);
>  
>  	nn_dbg(nn, "RV%02d: irq=%03d/%03d\n", idx, r_vec->irq_vector,
>  	       r_vec->irq_entry);
> @@ -840,7 +840,7 @@ nfp_net_prepare_vector(struct nfp_net *nn, struct nfp_net_r_vector *r_vec,
>  static void
>  nfp_net_cleanup_vector(struct nfp_net *nn, struct nfp_net_r_vector *r_vec)
>  {
> -	irq_set_affinity_hint(r_vec->irq_vector, NULL);
> +	irq_update_affinity_hint(r_vec->irq_vector, NULL);
>  	nfp_net_napi_del(&nn->dp, r_vec);
>  	free_irq(r_vec->irq_vector, r_vec);
>  }
Looks good to me, thank you!

Reviewed-by: Louis Peens <louis.peens@...igine.com>
> -- 
> 2.34.3
>