This fixes an issue where fairness is decreased since cfs_rq's can
end up not being decayed properly. For two sibling control groups with
the same priority, this can often lead to a load ratio of 99/1 (!!).
This happen because when a cfs_rq is throttled, all the descendant cfs_rq's
will be removed from the leaf list. When they initial cfs_rq is
unthrottled, it will currently only re add descendant cfs_rq's if they
have one or more entities enqueued. This is not a perfect heuristic.
Instead, we insert all cfs_rq's that contain one or more enqueued
entities, or it its load is not completely decayed.
Can often lead to situations like this for equally weighted control
groups:
$ ps u -C stress
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 10009 88.8 0.0 3676 100 pts/1 R+ 11:04 0:13 stress --cpu 1
root 10023 3.0 0.0 3676 104 pts/1 R+ 11:04 0:00 stress --cpu 1
Fixes: 31bc6aeaab1d ("sched/fair: Optimize update_blocked_averages()")
Signed-off-by: Odin Ugedal <odin@xxxxxxx>
---
Original thread: https://lore.kernel.org/lkml/20210518125202.78658-3-odin@xxxxxxx/
Changes since v1:
- Replaced cfs_rq field with using tg_load_avg_contrib
- Went from 3 to 1 patches; one is merged and one is replaced
by a new patchset.
Changes since v2:
- Use !cfs_rq_is_decayed() instead of tg_load_avg_contrib
- Moved cfs_rq_is_decayed to above its new use
kernel/sched/fair.c | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 794c2cb945f8..cdf6ac1a6b12 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -396,6 +396,23 @@ static inline void assert_list_leaf_cfs_rq(struct rq *rq)
list_for_each_entry_safe(cfs_rq, pos, &rq->leaf_cfs_rq_list, \
leaf_cfs_rq_list)
+static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
+{
+ if (cfs_rq->load.weight)
+ return false;
+
+ if (cfs_rq->avg.load_sum)
+ return false;
+
+ if (cfs_rq->avg.util_sum)
+ return false;
+
+ if (cfs_rq->avg.runnable_sum)
+ return false;
+
+ return true;
+}
+
/* Do the two (enqueued) entities belong to the same group ? */
static inline struct cfs_rq *
is_same_group(struct sched_entity *se, struct sched_entity *pse)
@@ -4719,8 +4736,8 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
cfs_rq->throttled_clock_task;
- /* Add cfs_rq with already running entity in the list */
- if (cfs_rq->nr_running >= 1)
+ /* Add cfs_rq with load or one or more already running entities to the list */
+ if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running)
list_add_leaf_cfs_rq(cfs_rq);
}
@@ -7895,23 +7912,6 @@ static bool __update_blocked_others(struct rq *rq, bool *done)
#ifdef CONFIG_FAIR_GROUP_SCHED
-static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
-{
- if (cfs_rq->load.weight)
- return false;
-
- if (cfs_rq->avg.load_sum)
- return false;
-
- if (cfs_rq->avg.util_sum)
- return false;
-
- if (cfs_rq->avg.runnable_sum)
- return false;
-
- return true;
-}
-
static bool __update_blocked_fair(struct rq *rq, bool *done)
{
struct cfs_rq *cfs_rq, *pos;
--
2.31.1
