hrtimer: Store cpu-number in struct hrtimer_cpu_base

In lowres mode, hrtimers are serviced by the tick instead of a clock
event. Now it works well as long as the tick stays periodic but we
must also make sure that the hrtimers are serviced in dynticks mode.

Part of that job consist in kicking a dynticks hrtimer target in order
to make it reconsider the next tick to schedule to correctly handle the
hrtimer's expiring time. And that part isn't handled by the hrtimers
subsystem.

To prepare for fixing this, we need __hrtimer_start_range_ns() to be
able to resolve the CPU target associated to a hrtimer's object
'cpu_base' so that the kick can be centralized there.

So lets store it in the 'struct hrtimer_cpu_base' to resolve the CPU
without overhead. It is set once at CPU's online notification.

Signed-off-by: Viresh Kumar <[e-mail]>
Signed-off-by: Frederic Weisbecker <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

include/linux/hrtimer.h

···
  * struct hrtimer_cpu_base - the per cpu clock bases
  * @lock:		lock protecting the base and associated clock bases
  *			and timers
+ * @cpu:		cpu number
  * @active_bases:	Bitfield to mark bases with active timers
  * @clock_was_set:	Indicates that clock was set from irq context.
  * @expires_next:	absolute time of the next event which was scheduled
···
  */
 struct hrtimer_cpu_base {
 	raw_spinlock_t			lock;
+	unsigned int			cpu;
 	unsigned int			active_bases;
 	unsigned int			clock_was_set;
 #ifdef CONFIG_HIGH_RES_TIMERS

kernel/time/hrtimer.c

···
 		timerqueue_init_head(&cpu_base->clock_base[i].active);
 	}
 
+	cpu_base->cpu = cpu;
 	hrtimer_init_hres(cpu_base);
 }