On Fri, Dec 17, 2021 at 06:02:23PM +0100, Paolo Bonzini wrote: > On 12/17/21 17:45, Paul E. McKenney wrote: > > 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? > > Yes, that code runs from ioctl(KVM_RUN) and the ioctl will return to the > calling process. Intriguing. A user process within the guest OS or a user process outside of any guest OS, that is, within the host? Thanx, Paul > Paolo > > > > * 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. ;-) > _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
