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Commit 2bbb6817 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Paul E. McKenney
Browse files

nohz: Allow rcu extended quiescent state handling seperately from tick stop 



It is assumed that rcu won't be used once we switch to tickless
mode and until we restart the tick. However this is not always
true, as in x86-64 where we dereference the idle notifiers after
the tick is stopped.

To prepare for fixing this, add two new APIs:
tick_nohz_idle_enter_norcu() and tick_nohz_idle_exit_norcu().

If no use of RCU is made in the idle loop between
tick_nohz_enter_idle() and tick_nohz_exit_idle() calls, the arch
must instead call the new *_norcu() version such that the arch doesn't
need to call rcu_idle_enter() and rcu_idle_exit().

Otherwise the arch must call tick_nohz_enter_idle() and
tick_nohz_exit_idle() and also call explicitly:

- rcu_idle_enter() after its last use of RCU before the CPU is put
to sleep.
- rcu_idle_exit() before the first use of RCU after the CPU is woken
up.

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: David Miller <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 280f0677

arch/arm/kernel/process.c

+2 −2
Original line number Original line Diff line number Diff line
@@ -183,7 +183,7 @@ void cpu_idle(void) 




	/* endless idle loop with no priority at all */

	/* endless idle loop with no priority at all */

	while (1) {

	while (1) {

		tick_nohz_idle_enter();

		tick_nohz_idle_enter_norcu();

		leds_event(led_idle_start);

		leds_event(led_idle_start);

		while (!need_resched()) {

		while (!need_resched()) {

#ifdef CONFIG_HOTPLUG_CPU

#ifdef CONFIG_HOTPLUG_CPU
@@ -213,7 +213,7 @@ void cpu_idle(void) 
			}

			}

		}

		}

		leds_event(led_idle_end);

		leds_event(led_idle_end);

		tick_nohz_idle_exit();

		tick_nohz_idle_exit_norcu();

		preempt_enable_no_resched();

		preempt_enable_no_resched();

		schedule();

		schedule();

		preempt_disable();

		preempt_disable();

arch/avr32/kernel/process.c

+2 −2
Original line number Original line Diff line number Diff line
@@ -34,10 +34,10 @@ void cpu_idle(void) 
{

{

	/* endless idle loop with no priority at all */

	/* endless idle loop with no priority at all */

	while (1) {

	while (1) {

		tick_nohz_idle_enter();

		tick_nohz_idle_enter_norcu();

		while (!need_resched())

		while (!need_resched())

			cpu_idle_sleep();

			cpu_idle_sleep();

		tick_nohz_idle_exit();

		tick_nohz_idle_exit_norcu();

		preempt_enable_no_resched();

		preempt_enable_no_resched();

		schedule();

		schedule();

		preempt_disable();

		preempt_disable();

arch/blackfin/kernel/process.c

+2 −2
Original line number Original line Diff line number Diff line
@@ -88,10 +88,10 @@ void cpu_idle(void) 
#endif

#endif

		if (!idle)

		if (!idle)

			idle = default_idle;

			idle = default_idle;

		tick_nohz_idle_enter();

		tick_nohz_idle_enter_norcu();

		while (!need_resched())

		while (!need_resched())

			idle();

			idle();

		tick_nohz_idle_exit();

		tick_nohz_idle_exit_norcu();

		preempt_enable_no_resched();

		preempt_enable_no_resched();

		schedule();

		schedule();

		preempt_disable();

		preempt_disable();

arch/microblaze/kernel/process.c

+2 −2
Original line number Original line Diff line number Diff line
@@ -103,10 +103,10 @@ void cpu_idle(void) 
		if (!idle)

		if (!idle)

			idle = default_idle;

			idle = default_idle;





		tick_nohz_idle_enter();

		tick_nohz_idle_enter_norcu();

		while (!need_resched())

		while (!need_resched())

			idle();

			idle();

		tick_nohz_idle_exit();

		tick_nohz_idle_exit_norcu();





		preempt_enable_no_resched();

		preempt_enable_no_resched();

		schedule();

		schedule();

arch/mips/kernel/process.c

+2 −2
Original line number Original line Diff line number Diff line
@@ -56,7 +56,7 @@ void __noreturn cpu_idle(void) 




	/* endless idle loop with no priority at all */

	/* endless idle loop with no priority at all */

	while (1) {

	while (1) {

		tick_nohz_idle_enter();

		tick_nohz_idle_enter_norcu();

		while (!need_resched() && cpu_online(cpu)) {

		while (!need_resched() && cpu_online(cpu)) {

#ifdef CONFIG_MIPS_MT_SMTC

#ifdef CONFIG_MIPS_MT_SMTC

			extern void smtc_idle_loop_hook(void);

			extern void smtc_idle_loop_hook(void);
@@ -77,7 +77,7 @@ void __noreturn cpu_idle(void) 
		     system_state == SYSTEM_BOOTING))

		     system_state == SYSTEM_BOOTING))

			play_dead();

			play_dead();

#endif

#endif

		tick_nohz_idle_exit();

		tick_nohz_idle_exit_norcu();

		preempt_enable_no_resched();

		preempt_enable_no_resched();

		schedule();

		schedule();

		preempt_disable();

		preempt_disable();