linux-kernel - Re: [PATCH] genirq: Keep affinity_hint unchanged if it has a value

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Message-ID: <87h63yzkb7.ffs@tglx>
Date: Wed, 12 Mar 2025 10:10:04 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Yajun Deng <yajun.deng@...ux.dev>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] genirq: Keep affinity_hint unchanged if it has a value

On Wed, Mar 12 2025 at 03:20, Yajun Deng wrote:
> March 11, 2025 at 10:14 PM, "Thomas Gleixner" <tglx@...utronix.de> wrote:
>> > For example, if affinity_hint points to smp_affinity, smp_affinity
>> >  is changed by the user, and affinity_hint would chang. affinity_hint
>> >  couldn't as a hint to the user, it should keep the value if it has.
>> 
>> What is 'smp_affinity'? 
>
> It's 'desc->irq_common_data.affinity'.

Which has no business to end up in the affinity hint.
 
>> I really fail to understand the problem you are trying to solve.
>
> irq_update_affinity_hint(irq, desc->irq_common_data.affinity);
>
> As in this code, this means affinity_hint points to smp_affinity.

This code does not exist and no driver should ever invoke
irq_update_affinity_hint() that way. The hint is a cpu mask managed by
the driver and not something the driver pulls out of a data structure
which it has no business to fiddle with.

Thanks

        tglx