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

["Yajun Deng" <yajun.deng@linux.dev>]

March 11, 2025 at 10:14 PM, "Thomas Gleixner" <tglx@linutronix.de> wrote:



> 
> On Tue, Mar 11 2025 at 09:33, Yajun Deng wrote:
> 
> > 
> > affinity_hint is a hint to user space for preferred irq affinity, but
> > 
> >  it could chang if the value it points to is changed. In other words,
> > 
> >  the hint is invalid.
> > 
> 
> That's a problem of the driver which provides the hint.
> 
> > 
> > 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'.
> 
> 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.

If someone were to bind several irqs to the same core, affinity_hint would change.

it couldn't as a hint to the user.

This patch allocates memory for affinity_hint and keeps the first value, even if someone

modifies smp_affinity, affinity_hint wouldn't change, it can as a hint to the user.


> 
> Thanks,
> 
>  tglx
>