[PATCH 3/4] sched/fair: Extend for_each_sched_entity() with a back-link

[Peter Zijlstra]

Leave a trail of bread crumbs, such that we can find out way back down the
hierarchy. No actual users yet, but split out because its a bit tricky.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/fair.c  |    9 +++++++--
 kernel/sched/sched.h |    1 +
 2 files changed, 8 insertions(+), 2 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -317,8 +317,13 @@ const struct sched_class fair_sched_clas
 #ifdef CONFIG_FAIR_GROUP_SCHED
 
 /* Walk up scheduling entities hierarchy */
-#define for_each_sched_entity(se, cfs_rq)				\
-	for (; (se) && ((cfs_rq) = cfs_rq_of(se)); (se) = (se)->parent)
+#define for_each_sched_entity(se, cfs_rq)					\
+	for (struct sched_entity *_BL = NULL;					\
+	     (se) && ((cfs_rq) = cfs_rq_of(se), (cfs_rq)->backlink = _BL, true);\
+	     (se) = (se)->parent, _BL = (se))
+
+#define for_each_sched_entity_bl(se, cfs_rq) \
+	for (; ((se) = (cfs_rq)->backlink); (cfs_rq) = group_cfs_rq(se))
 
 static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 {
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -726,6 +726,7 @@ struct cfs_rq {
 	unsigned long		tg_runnable_avg_contrib;
 	long			propagate;
 	long			prop_runnable_sum;
+	struct sched_entity	*backlink;
 
 	/*
 	 *   h_load = weight * f(tg)