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

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Message-ID: <20241110133128.GM4507@kernel.org>
Date: Sun, 10 Nov 2024 13:31:28 +0000
From: Simon Horman <horms@...nel.org>
To: Mohammad Heib <mheib@...hat.com>
Cc: netdev@...r.kernel.org, oss-drivers@...igine.com,
	louis.peens@...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>

Reviewed-by: Simon Horman <horms@...nel.org>