[PATCH tip/core/rcu 06/26] rcu: Ignore userspace extended quiescent state by default

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
	josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
	peterz@infradead.org, rostedt@goodmis.org,
	Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
	eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com,
	sbw@mit.edu, patches@linaro.org,
	Alessio Igor Bogani <abogani@kernel.org>,
	Avi Kivity <avi@redhat.com>, Chris Metcalf <cmetcalf@tilera.com>,
	Christoph Lameter <cl@linux.com>,
	Geoff Levand <geoff@infradead.org>,
	Gilad Ben Yossef <gilad@benyossef.com>,
	Hakan Akkan <hakanakkan@gmail.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>,
	Kevin Hilman <khilman@ti.com>,
	Max Krasnyansky <maxk@qualcomm.com>,
	Stephen Hemminger <shemminger@vyatta.com>,
	Sven-Thorsten Dietrich <thebigcorporation@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 06/26] rcu: Ignore userspace extended quiescent state by default
Date: Thu, 30 Aug 2012 14:05:23 -0700	[thread overview]
Message-ID: <1346360743-3628-6-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <1346360743-3628-1-git-send-email-paulmck@linux.vnet.ibm.com>

From: Frederic Weisbecker <fweisbec@gmail.com>

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>
---
 kernel/rcutree.c |    5 ++++-
 kernel/rcutree.h |    1 +
 2 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 8bbc7fb..e2fd370 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -210,6 +210,9 @@ 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. */
@@ -443,7 +446,7 @@ 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);
 	}
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 0dd5fd6..c190582 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -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
 };
-- 
1.7.8

