1 files changed, 68 insertions, 6 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 98e7eee..6eeae7e 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -644,7 +644,7 @@ struct rq {
 	unsigned long next_balance;
 	struct mm_struct *prev_mm;
 
-	unsigned int clock_skip_update;
+	unsigned int clock_update_flags;
 	u64 clock;
 	u64 clock_task;
 
@@ -768,48 +768,110 @@ static inline u64 __rq_clock_broken(struct rq *rq)
 	return READ_ONCE(rq->clock);
 }
 
+/*
+ * rq::clock_update_flags bits
+ *
+ * %RQCF_REQ_SKIP - will request skipping of clock update on the next
+ *  call to __schedule(). This is an optimisation to avoid
+ *  neighbouring rq clock updates.
+ *
+ * %RQCF_ACT_SKIP - is set from inside of __schedule() when skipping is
+ *  in effect and calls to update_rq_clock() are being ignored.
+ *
+ * %RQCF_UPDATED - is a debug flag that indicates whether a call has been
+ *  made to update_rq_clock() since the last time rq::lock was pinned.
+ *
+ * If inside of __schedule(), clock_update_flags will have been
+ * shifted left (a left shift is a cheap operation for the fast path
+ * to promote %RQCF_REQ_SKIP to %RQCF_ACT_SKIP), so you must use,
+ *
+ *	if (rq-clock_update_flags >= RQCF_UPDATED)
+ *
+ * to check if %RQCF_UPADTED is set. It'll never be shifted more than
+ * one position though, because the next rq_unpin_lock() will shift it
+ * back.
+ */
+#define RQCF_REQ_SKIP	0x01
+#define RQCF_ACT_SKIP	0x02
+#define RQCF_UPDATED	0x04
+
+static inline void assert_clock_updated(struct rq *rq)
+{
+	/*
+	 * The only reason for not seeing a clock update since the
+	 * last rq_pin_lock() is if we're currently skipping updates.
+	 */
+	SCHED_WARN_ON(rq->clock_update_flags < RQCF_ACT_SKIP);
+}
+
 static inline u64 rq_clock(struct rq *rq)
 {
 	lockdep_assert_held(&rq->lock);
+	assert_clock_updated(rq);
+
 	return rq->clock;
 }
 
 static inline u64 rq_clock_task(struct rq *rq)
 {
 	lockdep_assert_held(&rq->lock);
+	assert_clock_updated(rq);
+
 	return rq->clock_task;
 }
 
-#define RQCF_REQ_SKIP	0x01
-#define RQCF_ACT_SKIP	0x02
-
 static inline void rq_clock_skip_update(struct rq *rq, bool skip)
 {
 	lockdep_assert_held(&rq->lock);
 	if (skip)
-		rq->clock_skip_update |= RQCF_REQ_SKIP;
+		rq->clock_update_flags |= RQCF_REQ_SKIP;
 	else
-		rq->clock_skip_update &= ~RQCF_REQ_SKIP;
+		rq->clock_update_flags &= ~RQCF_REQ_SKIP;
 }
 
 struct rq_flags {
 	unsigned long flags;
 	struct pin_cookie cookie;
+#ifdef CONFIG_SCHED_DEBUG
+	/*
+	 * A copy of (rq::clock_update_flags & RQCF_UPDATED) for the
+	 * current pin context is stashed here in case it needs to be
+	 * restored in rq_repin_lock().
+	 */
+	unsigned int clock_update_flags;
+#endif
 };
 
 static inline void rq_pin_lock(struct rq *rq, struct rq_flags *rf)
 {
 	rf->cookie = lockdep_pin_lock(&rq->lock);
+
+#ifdef CONFIG_SCHED_DEBUG
+	rq->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
+	rf->clock_update_flags = 0;
+#endif
 }
 
 static inline void rq_unpin_lock(struct rq *rq, struct rq_flags *rf)
 {
+#ifdef CONFIG_SCHED_DEBUG
+	if (rq->clock_update_flags > RQCF_ACT_SKIP)
+		rf->clock_update_flags = RQCF_UPDATED;
+#endif
+
 	lockdep_unpin_lock(&rq->lock, rf->cookie);
 }
 
 static inline void rq_repin_lock(struct rq *rq, struct rq_flags *rf)
 {
 	lockdep_repin_lock(&rq->lock, rf->cookie);
+
+#ifdef CONFIG_SCHED_DEBUG
+	/*
+	 * Restore the value we stashed in @rf for this pin context.
+	 */
+	rq->clock_update_flags |= rf->clock_update_flags;
+#endif
 }
 
 #ifdef CONFIG_NUMA