In SMP system, to save power, not all cpus are active if system is not heavy loaded.
But let's image this case.
System is not heavy loaded - only cpu0 is active, but at some moment IRQ is issued very often in short time.
In this case, some of issued IRQs may be abandoned.
Let's assume a IC does abnormal operation if issued interrupt is not handled by MPU and system status is like above.
Then, system works abnormally when it is not loaded, but system works well when it is loaded.
(This is opposite of usual case. Most case, system may do abnormal operation when it is loaded.)
default IRQ affinity is usually, masked for all cores - IRQ can be handled by any cpu.
And, more than one cpus are active when system is loaded. So, there is less chance for IRQ to be abandoned - these are several cpus to handle!
This case shows very interesting issues at system!
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