Commit 1e1a689f authored Jul 11, 2012 by Frederic Weisbecker

rcu: Ignore userspace extended quiescent state by default

By default we don't want to enter into RCU extended quiescent
state while in userspace because doing this produces some overhead
(eg: use of syscall slowpath). Set it off by default and ready to
run when some feature like adaptive tickless need it.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

parent c5d900bf

kernel/rcutree.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -206,6 +206,9 @@ EXPORT_SYMBOL_GPL(rcu_note_context_switch);
		DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
		.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
		.dynticks = ATOMIC_INIT(1),
		#ifdef CONFIG_RCU_USER_QS
		.ignore_user_qs = true,
		#endif
		};

		static int blimit = 10; /* Maximum callbacks per rcu_do_batch. */
		@@ -430,7 +433,7 @@ void rcu_user_enter(void)

		local_irq_save(flags);
		rdtp = &__get_cpu_var(rcu_dynticks);
		if (!rdtp->in_user) {
		if (!rdtp->ignore_user_qs && !rdtp->in_user) {
		rdtp->in_user = true;
		rcu_eqs_enter(1);
		}

kernel/rcutree.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -103,6 +103,7 @@ struct rcu_dynticks {
		int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */
		#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
		#ifdef CONFIG_RCU_USER_QS
		bool ignore_user_qs; /* Treat userspace as extended QS or not */
		bool in_user; /* Is the CPU in userland from RCU POV? */
		#endif
		};