Re: [PATCH v2 2/5] perf: arm_cspmu: Support shared interrupts

On 2023-06-02 08:04, Ilkka Koskinen wrote:

Hi Robin,

On Thu, 1 Jun 2023, Robin Murphy wrote:

quoted

On 2023-06-01 04:01, Ilkka Koskinen wrote:

quoted

Some of the PMUs may share the interrupt. Support them by
setting IRQF_SHARED

This has the usual problem of allowing any PMU instance to move the 
IRQ affinity to a different CPU without also migrating all the other 
PMU contexts, and thus breaking perf core's assumptions of mutual 
exclusion.

I see, I wasn't aware of such an assumption. Sounds like there isn't 
necessarily an easy and clean solution for the shared interrupt case. I 
drop the patch and get back on the issue if we come up with something 
reasonable later.

What comes to mind is factoring out the explicit interrupt-sharing 
machinery that we wrote to solve this problem in arm_dmc620_pmu, or 
possibly trying to do something with IRQ affinity notifiers (however, I 
recall looking into that a while ago and it didn't seem like they 
actually interact with CPU hotplug in the way we'd want).

Thanks,
Robin.

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