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Old 07-23-2012, 05:24 PM
Luis Henriques
 
Default 2.6.32.x: hrtimer: Provide clock_was_set_delayed()

From: John Stultz <johnstul@us.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1020285

This is a backport of f55a6faa384304c89cfef162768e88374d3312cb

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>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
include/linux/hrtimer.h | 7 +++++++
kernel/hrtimer.c | 20 ++++++++++++++++++++
2 files changed, 27 insertions(+)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 040b679..a7f48af 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -159,6 +159,7 @@ struct hrtimer_clock_base {
* and timers
* @clock_base: array of clock bases for this cpu
* @curr_timer: the timer which is executing a callback right now
+ * @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
@@ -171,6 +172,7 @@ struct hrtimer_clock_base {
struct hrtimer_cpu_base {
spinlock_t lock;
struct hrtimer_clock_base clock_base[HRTIMER_MAX_CLOCK_BASES];
+ unsigned int clock_was_set;
#ifdef CONFIG_HIGH_RES_TIMERS
ktime_t expires_next;
int hres_active;
@@ -280,6 +282,8 @@ 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
@@ -308,6 +312,9 @@ static inline int hrtimer_is_hres_active(struct hrtimer *timer)
{
return 0;
}
+
+static inline void clock_was_set_delayed(void) { }
+
#endif

extern ktime_t ktime_get(void);
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index a6e9d00..c4acec7 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -738,6 +738,19 @@ 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; }
@@ -1393,6 +1406,13 @@ 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();
}

--
1.7.9.5


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