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

Hi Robin,

On Thu, 1 Jun 2023, Robin Murphy wrote:
> On 2023-06-01 04:01, Ilkka Koskinen wrote:
>> 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.

Cheers, Ilkka

>
> Thanks,
> Robin.
>
>> Signed-off-by: Ilkka Koskinen <ilkka@os.amperecomputing.com>
>> ---
>> drivers/perf/arm_cspmu/arm_cspmu.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c
>> b/drivers/perf/arm_cspmu/arm_cspmu.c
>> index 88547a2b73e6..cc5204d1b5fb 100644
>> --- a/drivers/perf/arm_cspmu/arm_cspmu.c
>> +++ b/drivers/perf/arm_cspmu/arm_cspmu.c
>> @@ -1067,8 +1067,8 @@ static int arm_cspmu_request_irq(struct arm_cspmu
>> *cspmu)
>> return irq;
>> ret = devm_request_irq(dev, irq, arm_cspmu_handle_irq,
>> - IRQF_NOBALANCING | IRQF_NO_THREAD,
>> dev_name(dev),
>> - cspmu);
>> + IRQF_NOBALANCING | IRQF_NO_THREAD |
>> IRQF_SHARED,
>> + dev_name(dev), cspmu);
>> if (ret) {
>> dev_err(dev, "Could not request IRQ %d\n", irq);
>> return ret;
>

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