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

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;
-- 
2.40.1

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.

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;

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;
>

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

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.