Messages in this thread | | | Date | Fri, 17 Dec 2021 17:34:04 +0100 | Subject | Re: Possible nohz-full/RCU issue in arm64 KVM | From | Paolo Bonzini <> |
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On 12/17/21 17:07, Paul E. McKenney wrote: >> rcu_note_context_switch() is a point-in-time notification; it's not strictly >> necessary, but it may improve performance a bit by avoiding unnecessary IPIs >> from the RCU subsystem. >> >> There's no benefit from doing it when you're back from the guest, because at >> that point the CPU is just running normal kernel code. > > Do scheduling-clock interrupts from guest mode have the "user" parameter > set? If so, that would keep RCU happy.
No, thread is in supervisor mode. But after every interrupt (timer tick or anything), one of three things can happen:
* KVM will go around the execution loop and invoke rcu_note_context_switch() again
* or KVM will go back to user space
* or the thread will be preempted
and either will keep RCU happy as far as I understand.
Paolo
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