Commit f32dd117 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

tick/broadcast: Make idle check independent from mode and config 



Currently the broadcast busy check, which prevents the idle code from
going into deep idle, works only in one shot mode.

If NOHZ and HIGHRES are off (config or command line) there is no
sanity check at all, so under certain conditions cpus are allowed to
go into deep idle, where the local timer stops, and are not woken up
again because there is no broadcast timer installed or a hrtimer based
broadcast device is not evaluated.

Move tick_broadcast_oneshot_control() into the common code and provide
proper subfunctions for the various config combinations.

The common check in tick_broadcast_oneshot_control() is for the C3STOP
misfeature flag of the local clock event device. If its not set, idle
can proceed. If set, further checks are necessary.

Provide checks for the trivial cases:

 - If broadcast is disabled in the config, then return busy

 - If oneshot mode (NOHZ/HIGHES) is disabled in the config, return
   busy if the broadcast device is hrtimer based.

 - If oneshot mode is enabled in the config call the original
   tick_broadcast_oneshot_control() function. That function needs
   extra checks which will be implemented in seperate patches.

[ Split out from a larger combo patch ]

Reported-and-tested-by: default avatarSudeep Holla <sudeep.holla@arm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Suzuki Poulose <Suzuki.Poulose@arm.com>
Cc: Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1507070929360.3916@nanos
parent e0454311

include/linux/tick.h

+0 −4
Original line number Diff line number Diff line
@@ -67,11 +67,7 @@ extern void tick_broadcast_control(enum tick_broadcast_mode mode); 
static inline void tick_broadcast_control(enum tick_broadcast_mode mode) { }

#endif /* BROADCAST */



#if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT)

extern int tick_broadcast_oneshot_control(enum tick_broadcast_state state);

#else

static inline int tick_broadcast_oneshot_control(enum tick_broadcast_state state) { return 0; }

#endif



static inline void tick_broadcast_enable(void)

{

kernel/time/tick-broadcast.c

+11 −15
Original line number Diff line number Diff line
@@ -685,18 +685,7 @@ static void broadcast_shutdown_local(struct clock_event_device *bc, 
	clockevents_switch_state(dev, CLOCK_EVT_STATE_SHUTDOWN);

}



/**

 * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode

 * @state:	The target state (enter/exit)

 *

 * The system enters/leaves a state, where affected devices might stop

 * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.

 *

 * Called with interrupts disabled, so clockevents_lock is not

 * required here because the local clock event device cannot go away

 * under us.

 */

int tick_broadcast_oneshot_control(enum tick_broadcast_state state)

int __tick_broadcast_oneshot_control(enum tick_broadcast_state state)

{

	struct clock_event_device *bc, *dev;

	struct tick_device *td;
@@ -717,9 +706,6 @@ int tick_broadcast_oneshot_control(enum tick_broadcast_state state) 
	td = this_cpu_ptr(&tick_cpu_device);

	dev = td->evtdev;



	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))

		return 0;



	raw_spin_lock(&tick_broadcast_lock);

	bc = tick_broadcast_device.evtdev;

	cpu = smp_processor_id();
@@ -961,6 +947,16 @@ bool tick_broadcast_oneshot_available(void) 
	return bc ? bc->features & CLOCK_EVT_FEAT_ONESHOT : false;

}



#else

int __tick_broadcast_oneshot_control(enum tick_broadcast_state state)

{

	struct clock_event_device *bc = tick_broadcast_device.evtdev;



	if (!bc || (bc->features & CLOCK_EVT_FEAT_HRTIMER))

		return -EBUSY;



	return 0;

}

#endif



void __init tick_broadcast_init(void)

kernel/time/tick-common.c

+21 −0
Original line number Diff line number Diff line
@@ -343,6 +343,27 @@ out_bc: 
	tick_install_broadcast_device(newdev);

}



/**

 * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode

 * @state:	The target state (enter/exit)

 *

 * The system enters/leaves a state, where affected devices might stop

 * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.

 *

 * Called with interrupts disabled, so clockevents_lock is not

 * required here because the local clock event device cannot go away

 * under us.

 */

int tick_broadcast_oneshot_control(enum tick_broadcast_state state)

{

	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);



	if (!(td->evtdev->features & CLOCK_EVT_FEAT_C3STOP))

		return 0;



	return __tick_broadcast_oneshot_control(state);

}



#ifdef CONFIG_HOTPLUG_CPU

/*

 * Transfer the do_timer job away from a dying cpu.

kernel/time/tick-sched.h

+10 −0
Original line number Diff line number Diff line
@@ -71,4 +71,14 @@ extern void tick_cancel_sched_timer(int cpu); 
static inline void tick_cancel_sched_timer(int cpu) { }

#endif



#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST

extern int __tick_broadcast_oneshot_control(enum tick_broadcast_state state);

#else

static inline int

__tick_broadcast_oneshot_control(enum tick_broadcast_state state)

{

	return -EBUSY;

}

#endif



#endif

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