Commit 126a6a54 authored Feb 10, 2015 by Rik van Riel Committed by Frederic Weisbecker Mar 09, 2015

kvm,rcu,nohz: use RCU extended quiescent state when running KVM guest



The host kernel is not doing anything while the CPU is executing
a KVM guest VCPU, so it can be marked as being in an extended
quiescent state, identical to that used when running user space
code.

The only exception to that rule is when the host handles an
interrupt, which is already handled by the irq code, which
calls rcu_irq_enter and rcu_irq_exit.

The guest_enter and guest_exit functions already switch vtime
accounting independent of context tracking. Leave those calls
where they are, instead of moving them into the context tracking
code.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will deacon <will.deacon@arm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

parent efc1e2c9

include/linux/context_tracking.h

+6 −0

Original line number	Diff line number	Diff line
		@@ -81,10 +81,16 @@ static inline void guest_enter(void)
		vtime_guest_enter(current);
		else
		current->flags \|= PF_VCPU;

		if (context_tracking_is_enabled())
		context_tracking_enter(CONTEXT_GUEST);
		}

		static inline void guest_exit(void)
		{
		if (context_tracking_is_enabled())
		context_tracking_exit(CONTEXT_GUEST);

		if (vtime_accounting_enabled())
		vtime_guest_exit(current);
		else

include/linux/context_tracking_state.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -15,6 +15,7 @@ struct context_tracking {
		enum ctx_state {
		CONTEXT_KERNEL = 0,
		CONTEXT_USER,
		CONTEXT_GUEST,
		} state;
		};

include/linux/kvm_host.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -766,6 +766,7 @@ static inline void kvm_guest_enter(void)
		* one time slice). Lets treat guest mode as quiescent state, just like
		* we do with user-mode execution.
		*/
		if (!context_tracking_cpu_is_enabled())
		rcu_virt_note_context_switch(smp_processor_id());
		}