Re: [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint

[Robin Murphy]

On 2021-05-17 19:08, Thomas Gleixner wrote:
> On Mon, May 17 2021 at 18:26, Robin Murphy wrote:
> > On 2021-05-17 17:57, Nitesh Lal wrote:
> > I'm not implying that there isn't a bug, or that this code ever made
> > sense in the first place, just that fixing it will unfortunately be a
> > bit more involved than a simple revert. This patch as-is *will* subtly
> > break at least the system PMU drivers currently using
>
> s/using/abusing/
>
> > irq_set_affinity_hint() - those I know require the IRQ affinity to
> > follow whichever CPU the PMU context is bound to, in order to meet perf
> > core's assumptions about mutual exclusion.
>
> Which driver is that?

Right now, any driver which wants to control an IRQ's affinity and also 
build as a module, for one thing. I'm familiar with drivers/perf/ where 
a basic pattern has been widely copied; some of the callers in other 
subsystems appear to *expect* it to set the underlying affinity as well, 
but whether any of those added within the last 6 years represent a 
functional dependency rather than just a performance concern I don't know.

Robin.