sched/features: Distinguish between NORMAL and DEADLINE hrtick

The HRTICK feature has traditionally been servicing configurations that
need precise preemptions point for NORMAL tasks. More recently, the
feature has been extended to also service DEADLINE tasks with stringent
runtime enforcement needs (e.g., runtime < 1ms with HZ=1000).

Enabling HRTICK sched feature currently enables the additional timer and
task tick for both classes, which might introduced undesired overhead
for no additional benefit if one needed it only for one of the cases.

Separate HRTICK sched feature in two (and leave the traditional case
name unmodified) so that it can be selectively enabled when needed.

With:

  $ echo HRTICK > /sys/kernel/debug/sched_features

the NORMAL/fair hrtick gets enabled.

With:

  $ echo HRTICK_DL > /sys/kernel/debug/sched_features

the DEADLINE hrtick gets enabled.

Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210208073554.14629-3-juri.lelli@redhat.com

1 files changed, 24 insertions, 2 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0dfdd52799c7..10a1522b1e30 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2105,17 +2105,39 @@ extern const_debug unsigned int sysctl_sched_migration_cost;
  */
 static inline int hrtick_enabled(struct rq *rq)
 {
-	if (!sched_feat(HRTICK))
-		return 0;
 	if (!cpu_active(cpu_of(rq)))
 		return 0;
 	return hrtimer_is_hres_active(&rq->hrtick_timer);
 }
 
+static inline int hrtick_enabled_fair(struct rq *rq)
+{
+	if (!sched_feat(HRTICK))
+		return 0;
+	return hrtick_enabled(rq);
+}
+
+static inline int hrtick_enabled_dl(struct rq *rq)
+{
+	if (!sched_feat(HRTICK_DL))
+		return 0;
+	return hrtick_enabled(rq);
+}
+
 void hrtick_start(struct rq *rq, u64 delay);
 
 #else
 
+static inline int hrtick_enabled_fair(struct rq *rq)
+{
+	return 0;
+}
+
+static inline int hrtick_enabled_dl(struct rq *rq)
+{
+	return 0;
+}
+
 static inline int hrtick_enabled(struct rq *rq)
 {
 	return 0;