On Fri, Dec 17, 2021 at 05:34:04PM +0100, Paolo Bonzini wrote: > 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 Here "user space" is a user process as opposed to a guest OS? > * or the thread will be preempted > > and either will keep RCU happy as far as I understand. Regardless of the answer to my question above, yes, these will keep RCU happy. ;-) Thanx, Paul _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
