Messages in this thread | | | From | Hardik H Bagdi <> | Date | Thu, 26 Jan 2017 09:12:34 -0500 | Subject | Understanding stop_machine() use for cpu_down() |
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Hi,
I'm trying to understand why stop_machine() is necessary for cpu_down() operation.
I see that multi_cpu_stop() on every online cpu (which hogs the cpu and then triggers state changes state) and then, take_cpu_down is invoked on the outgoing cpu. This happens by every cpu decrementing the msdata->thread_ack and last one trigger a state change.
I'm trying to understand why is this necessary.
Is to wait for RCU grace period(s)? If yes, what variable/struct is being protected and how does stop_machine() help there?
I see there was a patch (https://lwn.net/Articles/538819/) but had some issues with idle_loop.
Is there an alternative where the stop_machine would not be necessary? Or more specifically, is there a reason why every CPU would need to stop?
Any help would be appreciated.
Thanks, Hardik
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