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

[Ilkka Koskinen]

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@xxxxxxxxxxxxxxxxxxxxxx>
> > ---
> >   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;