Re: Possible nohz-full/RCU issue in arm64 KVM
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: 2021-12-17 16:45:38
Also in:
kvmarm, lkml, rcu
On Fri, Dec 17, 2021 at 05:34:04PM +0100, Paolo Bonzini wrote:
On 12/17/21 17:07, Paul E. McKenney wrote:quoted
quoted
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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel