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Subject[patch V2 05/10] timer: Retrieve next expiry of pinned/non-pinned timers seperately
To prepare for the conversion of the NOHZ timer placement to a pull at
expiry time model it's required to have seperate expiry times for the
pinned and the non-pinned (movable) timers.

No functional change

Signed-off-by: Richard Cochran <rcochran@linutronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
kernel/time/tick-internal.h | 3 ++-
kernel/time/tick-sched.c | 10 ++++++----
kernel/time/timer.c | 41 +++++++++++++++++++++++++++++++++++------
3 files changed, 43 insertions(+), 11 deletions(-)

--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -163,5 +163,6 @@ static inline void timers_update_migrati

DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases);

-extern u64 get_next_timer_interrupt(unsigned long basej, u64 basem);
+extern u64 get_next_timer_interrupt(unsigned long basej, u64 basem,
+ u64 *global_evt);
void timer_clear_idle(void);
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -666,7 +666,7 @@ static ktime_t tick_nohz_stop_sched_tick
ktime_t now, int cpu)
{
struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
- u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
+ u64 basemono, next_tick, next_local, next_global, next_rcu, delta, expires;
unsigned long seq, basejiff;
ktime_t tick;

@@ -689,10 +689,12 @@ static ktime_t tick_nohz_stop_sched_tick
* disabled this also looks at the next expiring
* hrtimer.
*/
- next_tmr = get_next_timer_interrupt(basejiff, basemono);
- ts->next_timer = next_tmr;
+ next_local = get_next_timer_interrupt(basejiff, basemono,
+ &next_global);
+ next_local = min(next_local, next_global);
+ ts->next_timer = next_local;
/* Take the next rcu event into account */
- next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
+ next_tick = next_rcu < next_local ? next_rcu : next_local;
}

/*
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1472,23 +1472,27 @@ static u64 cmp_next_hrtimer_event(u64 ba
* get_next_timer_interrupt - return the time (clock mono) of the next timer
* @basej: base time jiffies
* @basem: base time clock monotonic
+ * @global_evt: Pointer to store the expiry time of the next global timer
*
* Returns the tick aligned clock monotonic time of the next pending
* timer or KTIME_MAX if no timer is pending.
*/
-u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
+u64 get_next_timer_interrupt(unsigned long basej, u64 basem, u64 *global_evt)
{
unsigned long nextevt, nextevt_local, nextevt_global;
bool local_empty, global_empty, local_first, is_idle;
struct timer_base *base_local, *base_global;
- u64 expires = KTIME_MAX;
+ u64 local_evt = KTIME_MAX;
+
+ /* Preset global event */
+ *global_evt = KTIME_MAX;

/*
* Pretend that there is no timer pending if the cpu is offline.
* Possible pending timers will be migrated later to an active cpu.
*/
if (cpu_is_offline(smp_processor_id()))
- return expires;
+ return local_evt;

base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
base_global = this_cpu_ptr(&timer_bases[BASE_GLOBAL]);
@@ -1532,14 +1536,39 @@ u64 get_next_timer_interrupt(unsigned lo
spin_unlock(&base_local->lock);
spin_unlock(&base_global->lock);

- if (!local_empty || !global_empty) {
+ /*
+ * If the bases are not marked idle, i.e one of the events is at
+ * max. one tick away, use the next event for calculating next
+ * local expiry value. The next global event is left as KTIME_MAX,
+ * so this CPU will not queue itself in the global expiry
+ * mechanism.
+ */
+ if (!is_idle) {
/* If we missed a tick already, force 0 delta */
if (time_before_eq(nextevt, basej))
nextevt = basej;
- expires = basem + (nextevt - basej) * TICK_NSEC;
+ local_evt = basem + (nextevt - basej) * TICK_NSEC;
+ return cmp_next_hrtimer_event(basem, local_evt);
}

- return cmp_next_hrtimer_event(basem, expires);
+ /*
+ * If the bases are marked idle, i.e. the next event on both the
+ * local and the global queue are farther away than a tick,
+ * evaluate both bases. No need to check whether one of the bases
+ * has an already expired timer as this is caught by the !is_idle
+ * condition above.
+ */
+ if (!local_empty)
+ local_evt = basem + (nextevt_local - basej) * TICK_NSEC;
+
+ /*
+ * If the local queue expires first, there is no requirement for
+ * queuing the CPU in the global expiry mechanism.
+ */
+ if (!local_first && !global_empty)
+ *global_evt = basem + (nextevt_global - basej) * TICK_NSEC;
+
+ return cmp_next_hrtimer_event(basem, local_evt);
}

/**

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