From: Hardik H Bagdi <hbagdi1@binghamton.edu>
To: linux-hotplug@vger.kernel.org
Subject: Understanding stop_machine() use for cpu_down()
Date: Wed, 25 Jan 2017 23:41:53 +0000 [thread overview]
Message-ID: <CADdiZBT-wvAmmtRem1=arnvPcyJrgH3s43ngAuzqk3poHe-FJA@mail.gmail.com> (raw)
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
next reply other threads:[~2017-01-25 23:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-25 23:41 Hardik H Bagdi [this message]
2017-01-26 7:10 ` Understanding stop_machine() use for cpu_down() Greg KH
2017-01-26 14:09 ` Hardik H Bagdi
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