Messages in this thread | | | Subject | Re: How to know if there is a pending interrupt when they are masked? | From | Daniel Lezcano <> | Date | Thu, 14 Feb 2019 17:16:07 +0100 |
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Hi Thomas,
thanks for the answer,
On 14/02/2019 16:47, Marc Zyngier wrote: > On 14/02/2019 15:35, Thomas Gleixner wrote: >> On Thu, 14 Feb 2019, Daniel Lezcano wrote: >>> today we have the possibility to mask the local interrupt with the >>> command local_irq_disable / local_irq_enable. >>> >>> The power management path disables the local interrupt in order to >>> initiate a power down sequence. If there is a pending interrupt this one >>> will make the power down function to abort, thus exiting right after >>> calling the shutdown function after costly operations. It could be >>> interesting to check if there is a pending interrupt before initiating >>> the power down sequence. >>> >>> Is there a way to know if there is a pending interrupt on the current >>> CPU when the local interrupt are disabled? Something like, >>> local_irq_pending() function ? >> >> We have nothing like that today, but it would be possible to implement this >> at least on x86 by peeking the local APIC registers. > > On arm64, reading ISR_EL1 would give some indication of that, but...
Does 'some indication' means as soon as we read the ISR_EL1 it may be outdated right after ?
>> OTOH, the question is whether it's worth the trouble because the interrupt >> could come in right after the query and the same issue which you want to >> address persists. It only makes sense if it reduces the time window so >> significantly that it actually matters. > > as Thomas explains, the potential race is pretty tight.
Is a simple hack possible on ARM64 to check if it is worth or not?
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