Messages in this thread | | | Date | Thu, 10 May 2018 11:21:14 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] armpmu: broadcast overflow irq on multi-core system having one muxed SPI for PMU. |
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Hi, On Thu, May 10, 2018 at 05:36:17PM +0900, Hoeun Ryu wrote: > From: Hoeun Ryu <hoeun.ryu@lge.com> > > On some SoCs like i.MX6DL/QL have only one muxed SPI for multi-core system. > On the systems, a CPU can be interrupted by overflow irq but it is possible that > the overflow actually occurs on another CPU.
Muxing the PMU IRQs is a really broken system design, and there's no good way of supporting it.
What we should do for such systems is:
* Add a flag to the DT to describe that the IRQs are muxed, as this cannot be probed.
* Add hrtimer code to periodically update the counters, to avoid overflow (e.g. as we do in the l2x0 PMU).
* Reject sampling for such systems, as this cannot be done reliably or efficiently.
NAK to broadcasting the IRQ -- there are a number of issues with the general approach.
We should update the PMU probing code to warn when we have fewer IRQs than CPUs, and fail gracefully to the above.
[...]
> static irqreturn_t armpmu_dispatch_irq(int irq, void *dev) > {
> + /* smp_call_function cannot be called with irq disabled */ > + local_irq_enable(); > + preempt_disable(); > + smp_call_function_many(&mask, __armpmu_handle_irq, dev, 0); > + preempt_enable(); > + local_irq_disable();
For many reasons, this sequence is not safe.
It is not safe to enable IRQs in irq handlers. Please never do this.
Thus it's also never safe to call smp_call_function*() in IRQ handlers.
Futher, If you ever encounter a case where you need to avoid preemption across enabling IRQs, preemption must be disabled *before* enabling IRQs.
Thanks, Mark.
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