sched: Keep at least 1 tick per second for active dynticks tasks

The scheduler doesn't yet fully support environments
with a single task running without a periodic tick.

In order to ensure we still maintain the duties of scheduler_tick(),
keep at least 1 tick per second.

This makes sure that we keep the progression of various scheduler
accounting and background maintainance even with a very low granularity.
Examples include cpu load, sched average, CFS entity vruntime,
avenrun and events such as load balancing, amongst other details
handled in sched_class::task_tick().

This limitation will be removed in the future once we get
these individual items to work in full dynticks CPUs.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 10 insertions, 0 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 24dc298..ce39224d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -410,6 +410,9 @@ struct rq {
 	u64 nohz_stamp;
 	unsigned long nohz_flags;
 #endif
+#ifdef CONFIG_NO_HZ_FULL
+	unsigned long last_sched_tick;
+#endif
 	int skip_clock_update;
 
 	/* capture load from *all* tasks on this cpu: */
@@ -1090,6 +1093,13 @@ static inline void dec_nr_running(struct rq *rq)
 	rq->nr_running--;
 }
 
+static inline void rq_last_tick_reset(struct rq *rq)
+{
+#ifdef CONFIG_NO_HZ_FULL
+	rq->last_sched_tick = jiffies;
+#endif
+}
+
 extern void update_rq_clock(struct rq *rq);
 
 extern void activate_task(struct rq *rq, struct task_struct *p, int flags);