[PATCH v2 04/12] sched/core: Make __update_rq_clock() skip updates on UPDATED

[Peter Zijlstra <peterz@infradead.org>]

Calling update_rq_clock() on a rq which is already up-to-date would still move
the clock (after warning when WARN_DOUBLE_CLOCK is set). This is a bit silly,
so also skip the update when already up-to-date.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/core.c  |    7 +++++--
 kernel/sched/sched.h |    2 ++
 2 files changed, 7 insertions(+), 2 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -869,11 +869,14 @@ static void update_rq_clock_task(struct
 
 static void __update_rq_clock(struct rq *rq)
 {
+	bool update;
+
 	lockdep_assert_rq_held(rq);
 
+	update = !(rq->clock_update_flags & RQCF_NOP_MASK);
 	rq->clock_update_flags |= RQCF_UPDATED;
 
-	if (!(rq->clock_update_flags & RQCF_ACT_SKIP)) {
+	if (update) {
 		u64 clock = sched_clock_cpu(cpu_of(rq));
 		s64 delta;
 
@@ -890,7 +893,7 @@ static void __update_rq_clock(struct rq
 void update_rq_clock(struct rq *rq)
 {
 	if (sched_feat(WARN_DOUBLE_CLOCK))
-		WARN_ON_ONCE(rq->clock_update_flags & RQCF_UPDATED);
+		WARN_ON_ONCE((rq->clock_update_flags & RQCF_NOP_MASK) == RQCF_UPDATED);
 
 	__update_rq_clock(rq);
 }
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1807,6 +1807,8 @@ extern void update_rq_clock(struct rq *r
 #define RQCF_ACT_SKIP		0x02
 #define RQCF_UPDATED		0x04
 
+#define RQCF_NOP_MASK		(RQCF_ACT_SKIP | RQCF_UPDATED)
+
 static inline void assert_clock_updated(struct rq *rq)
 {
 	/*