sched: Migrate sched to use new tick dependency mask model

Instead of providing asynchronous checks for the nohz subsystem to verify
sched tick dependency, migrate sched to the new mask.

Everytime a task is enqueued or dequeued, we evaluate the state of the
tick dependency on top of the policy of the tasks in the runqueue, by
order of priority:

SCHED_DEADLINE: Need the tick in order to periodically check for runtime
SCHED_FIFO    : Don't need the tick (no round-robin)
SCHED_RR      : Need the tick if more than 1 task of the same priority
                for round robin (simplified with checking if more than
                one SCHED_RR task no matter what priority).
SCHED_NORMAL  : Need the tick if more than 1 task for round-robin.

We could optimize that further with one flag per sched policy on the tick
dependency mask and perform only the checks relevant to the policy
concerned by an enqueue/dequeue operation.

Since the checks aren't based on the current task anymore, we could get
rid of the task switch hook but it's still needed for posix cpu
timers.

Reviewed-by: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

1 files changed, 0 insertions, 5 deletions

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 3f79def37ca9..f312c60c3ed2 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -204,11 +204,6 @@ static bool can_stop_full_tick(struct tick_sched *ts)
 		return false;
 	}
 
-	if (!sched_can_stop_tick()) {
-		trace_tick_stop(0, TICK_DEP_MASK_SCHED);
-		return false;
-	}
-
 	if (!posix_cpu_timers_can_stop_tick(current)) {
 		trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
 		return false;