Merge branch 'timers/core-v9' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/nohz

Pull nohz enhancements from Frederic Weisbecker:

"Currently in nohz full configs, the tick dependency is checked
 asynchronously by nohz code from interrupt and context switch for each
 concerned subsystem with a set of function provided by these. Such
 functions are made of many conditions and details that can be heavyweight
 as they are called on fastpath: sched_can_stop_tick(),
 posix_cpu_timer_can_stop_tick(), perf_event_can_stop_tick()...

 Thomas suggested a few months ago to make that tick dependency check
 synchronous. Instead of checking subsystems details from each interrupt
 to guess if the tick can be stopped, every subsystem that may have a tick
 dependency should set itself a flag specifying the state of that
 dependency. This way we can verify if we can stop the tick with a single
 lightweight mask check on fast path.

 This conversion from a pull to a push model to implement tick dependency
 is the core feature of this patchset that is split into:

  * Nohz wide kick simplification
  * Improve nohz tracing
  * Introduce tick dependency mask
  * Migrate scheduler, posix timers, perf events and sched clock tick
    dependencies to the tick dependency mask."

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 20 insertions, 29 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9503d590e5ef..1fad82364ffe 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -453,20 +453,6 @@ static inline void init_hrtick(void)
 }
 #endif	/* CONFIG_SCHED_HRTICK */
 
-/*
- * cmpxchg based fetch_or, macro so it works for different integer types
- */
-#define fetch_or(ptr, val)						\
-({	typeof(*(ptr)) __old, __val = *(ptr);				\
- 	for (;;) {							\
- 		__old = cmpxchg((ptr), __val, __val | (val));		\
- 		if (__old == __val)					\
- 			break;						\
- 		__val = __old;						\
- 	}								\
- 	__old;								\
-})
-
 #if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
 /*
  * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
@@ -715,31 +701,36 @@ static inline bool got_nohz_idle_kick(void)
 #endif /* CONFIG_NO_HZ_COMMON */
 
 #ifdef CONFIG_NO_HZ_FULL
-bool sched_can_stop_tick(void)
+bool sched_can_stop_tick(struct rq *rq)
 {
+	int fifo_nr_running;
+
+	/* Deadline tasks, even if single, need the tick */
+	if (rq->dl.dl_nr_running)
+		return false;
+
 	/*
-	 * FIFO realtime policy runs the highest priority task. Other runnable
-	 * tasks are of a lower priority. The scheduler tick does nothing.
+	 * FIFO realtime policy runs the highest priority task (after DEADLINE).
+	 * Other runnable tasks are of a lower priority. The scheduler tick
+	 * isn't needed.
 	 */
-	if (current->policy == SCHED_FIFO)
+	fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running;
+	if (fifo_nr_running)
 		return true;
 
 	/*
 	 * Round-robin realtime tasks time slice with other tasks at the same
-	 * realtime priority. Is this task the only one at this priority?
+	 * realtime priority.
 	 */
-	if (current->policy == SCHED_RR) {
-		struct sched_rt_entity *rt_se = &current->rt;
-
-		return list_is_singular(&rt_se->run_list);
+	if (rq->rt.rr_nr_running) {
+		if (rq->rt.rr_nr_running == 1)
+			return true;
+		else
+			return false;
 	}
 
-	/*
-	 * More than one running task need preemption.
-	 * nr_running update is assumed to be visible
-	 * after IPI is sent from wakers.
-	 */
-	if (this_rq()->nr_running > 1)
+	/* Normal multitasking need periodic preemption checks */
+	if (rq->cfs.nr_running > 1)
 		return false;
 
 	return true;