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hrtimer: Provide clock_was_set_delayed()

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clock_was_set() cannot be called from hard interrupt context because
it calls on_each_cpu().

For fixing the widely reported leap seconds issue it is necessary to
call it from hard interrupt context, i.e. the timer tick code, which
does the timekeeping updates.

Provide a new function which denotes it in the hrtimer cpu base
structure of the cpu on which it is called and raise the hrtimer
softirq. We then execute the clock_was_set() notificiation from
softirq context in run_hrtimer_softirq(). The hrtimer softirq is
rarely used, so polling the flag there is not a performance issue.

[ tglx: Made it depend on CONFIG_HIGH_RES_TIMERS. We really should get
  rid of all this ifdeffery ASAP ]

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Reported-by: Jan Engelhardt <jengelh@inai.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1341960205-56738-2-git-send-email-johnstul@us.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
John Stultz 2012-07-10 18:43:19 -04:00 • committed by Thomas Gleixner
commit f55a6faa38
2 changed files with 28 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

9
include/linux/hrtimer.h
View file

@ -165,6 +165,7 @@ enum hrtimer_base_type {
* @lock: lock protecting the base and associated clock bases
* and timers
* @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
* via clock_set_next_event()
* @hres_active: State of high resolution mode
@ -177,7 +178,8 @@ enum hrtimer_base_type {
*/
struct hrtimer_cpu_base {
raw_spinlock_t lock;
unsigned long active_bases;
unsigned int active_bases;
unsigned int clock_was_set;
#ifdef CONFIG_HIGH_RES_TIMERS
ktime_t expires_next;
int hres_active;
@ -286,6 +288,8 @@ extern void hrtimer_peek_ahead_timers(void);
# define MONOTONIC_RES_NSEC HIGH_RES_NSEC
# define KTIME_MONOTONIC_RES KTIME_HIGH_RES
extern void clock_was_set_delayed(void);
#else
# define MONOTONIC_RES_NSEC LOW_RES_NSEC
@ -306,6 +310,9 @@ static inline int hrtimer_is_hres_active(struct hrtimer *timer)
{
return 0;
}
static inline void clock_was_set_delayed(void) { }
#endif
extern void clock_was_set(void);

20
kernel/hrtimer.c
View file

@ -717,6 +717,19 @@ static int hrtimer_switch_to_hres(void)
return 1;
}
/*
* Called from timekeeping code to reprogramm the hrtimer interrupt
* device. If called from the timer interrupt context we defer it to
* softirq context.
*/
void clock_was_set_delayed(void)
{
struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
cpu_base->clock_was_set = 1;
__raise_softirq_irqoff(HRTIMER_SOFTIRQ);
}
#else
static inline int hrtimer_hres_active(void) { return 0; }
@ -1395,6 +1408,13 @@ void hrtimer_peek_ahead_timers(void)
static void run_hrtimer_softirq(struct softirq_action *h)
{
struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
if (cpu_base->clock_was_set) {
cpu_base->clock_was_set = 0;
clock_was_set();
}
hrtimer_peek_ahead_timers();
}