Re: Possible nohz-full/RCU issue in arm64 KVM
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: 2021-12-17 16:07:53
Also in:
kvmarm, lkml, rcu
On Fri, Dec 17, 2021 at 04:54:22PM +0100, Paolo Bonzini wrote:
On 12/17/21 15:38, Mark Rutland wrote:quoted
For example kvm_guest_enter_irqoff() calls guest_enter_irq_off() which calls vtime_account_guest_enter(), but kvm_guest_exit_irqoff() doesn't call guest_exit_irq_off() and the call to vtime_account_guest_exit() is open-coded elsewhere. Also, guest_enter_irq_off() conditionally calls rcu_virt_note_context_switch(), but I can't immediately spot anything on the exit side that corresponded with that, which looks suspicious.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. Thanx, Paul _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel