Commit eaa907c5 authored Mar 06, 2013 by Thomas Gleixner

tick: Provide a check for a forced broadcast pending



On the CPU which gets woken along with the target CPU of the broadcast
the following happens:

  deep_idle()
			<-- spurious wakeup
  broadcast_exit()
    set forced bit
  
  enable interrupts
    
			<-- Nothing happens

  disable interrupts

  broadcast_enter()
			<-- Here we observe the forced bit is set
  deep_idle()

Now after that the target CPU of the broadcast runs the broadcast
handler and finds the other CPU in both the broadcast and the forced
mask, sends the IPI and stuff gets back to normal.

So it's not actually harmful, just more evidence for the theory, that
hardware designers have access to very special drug supplies.

Now there is no point in going back to deep idle just to wake up again
right away via an IPI. Provide a check which allows the idle code to
avoid the deep idle transition.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: LAK <linux-arm-kernel@lists.infradead.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Arjan van de Veen <arjan@infradead.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Jason Liu <liu.h.jason@gmail.com>
Link: http://lkml.kernel.org/r/20130306111537.565418308@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

parent 989dcb64

include/linux/clockchips.h

+6 −0

Original line number	Diff line number	Diff line
		@@ -175,6 +175,12 @@ extern void tick_broadcast(const struct cpumask *mask);
		extern int tick_receive_broadcast(void);
		#endif

		#if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT)
		extern int tick_check_broadcast_expired(void);
		#else
		static inline int tick_check_broadcast_expired(void) { return 0; }
		#endif

		#ifdef CONFIG_GENERIC_CLOCKEVENTS
		extern void clockevents_notify(unsigned long reason, void *arg);
		#else

kernel/time/tick-broadcast.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -403,6 +403,18 @@ struct cpumask *tick_get_broadcast_oneshot_mask(void)
		return tick_broadcast_oneshot_mask;
		}

		/*
		* Called before going idle with interrupts disabled. Checks whether a
		* broadcast event from the other core is about to happen. We detected
		* that in tick_broadcast_oneshot_control(). The callsite can use this
		* to avoid a deep idle transition as we are about to get the
		* broadcast IPI right away.
		*/
		int tick_check_broadcast_expired(void)
		{
		return cpumask_test_cpu(smp_processor_id(), tick_broadcast_force_mask);
		}

		/*
		* Set broadcast interrupt affinity
		*/

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