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linuxkernelarmcpupython-idle

Linux kernel idle loop

Inside the linux kernel idle loop, for quite a few architectures (SH, ARM, X86 etc.. afaik) are the following lines:

if(cpuidle_idle_call())
    pm_idle();

My doubt:

At-least for ARM, The default pm_idle function consists of WFI (Wait for interrupt) instruction but the confusing part is, interrupts are disabled then and are enabled after the WFI instruction executes, How does a CPU get back online from WFI when interrupts were disabled ?

I tried searching for my answers in various versions of linux, but the related code is unchanged since 2.6.32 (the last version i referred to) so it's more likely that I am missing something.

Solution

  • WFI wakes even if interrupts are disabled, but the ARM core doesn't receive the interrupts until interrupts are enabled again.