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

- From: Robin Murphy \<robin.murphy@arm.com\>
- Date: 2021-05-17 18:50:48 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2021/05/1381100
- Thread: https://ratatoskr.run/linux-api/2021/05/6355345/t.md

```text
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.
```