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authorRik van Riel <riel@surriel.com>2021-06-21 19:43:30 +0200
committerIngo Molnar <mingo@kernel.org>2021-06-22 14:06:57 +0200
commitfdaba61ef8a268d4136d0a113d153f7a89eb9984 (patch)
treed2fd026e595d2b5eabbe15aadd3dc6382f55d240 /kernel/sched
parenta96bfed64c8986d6404e553f18203cae1f5ac7e6 (diff)
sched/fair: Ensure that the CFS parent is added after unthrottling
Ensure that a CFS parent will be in the list whenever one of its children is also in the list. A warning on rq->tmp_alone_branch != &rq->leaf_cfs_rq_list has been reported while running LTP test cfs_bandwidth01. Odin Ugedal found the root cause: $ tree /sys/fs/cgroup/ltp/ -d --charset=ascii /sys/fs/cgroup/ltp/ |-- drain `-- test-6851 `-- level2 |-- level3a | |-- worker1 | `-- worker2 `-- level3b `-- worker3 Timeline (ish): - worker3 gets throttled - level3b is decayed, since it has no more load - level2 get throttled - worker3 get unthrottled - level2 get unthrottled - worker3 is added to list - level3b is not added to list, since nr_running==0 and is decayed [ Vincent Guittot: Rebased and updated to fix for the reported warning. ] Fixes: a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to list on unthrottle") Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> Suggested-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Rik van Riel <riel@surriel.com> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com> Acked-by: Odin Ugedal <odin@uged.al> Link: https://lore.kernel.org/r/20210621174330.11258-1-vincent.guittot@linaro.org
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/fair.c28
1 files changed, 28 insertions, 0 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bfaa6e1f6067..23663318fb81 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3298,6 +3298,31 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
#ifdef CONFIG_SMP
#ifdef CONFIG_FAIR_GROUP_SCHED
+/*
+ * Because list_add_leaf_cfs_rq always places a child cfs_rq on the list
+ * immediately before a parent cfs_rq, and cfs_rqs are removed from the list
+ * bottom-up, we only have to test whether the cfs_rq before us on the list
+ * is our child.
+ * If cfs_rq is not on the list, test whether a child needs its to be added to
+ * connect a branch to the tree * (see list_add_leaf_cfs_rq() for details).
+ */
+static inline bool child_cfs_rq_on_list(struct cfs_rq *cfs_rq)
+{
+ struct cfs_rq *prev_cfs_rq;
+ struct list_head *prev;
+
+ if (cfs_rq->on_list) {
+ prev = cfs_rq->leaf_cfs_rq_list.prev;
+ } else {
+ struct rq *rq = rq_of(cfs_rq);
+
+ prev = rq->tmp_alone_branch;
+ }
+
+ prev_cfs_rq = container_of(prev, struct cfs_rq, leaf_cfs_rq_list);
+
+ return (prev_cfs_rq->tg->parent == cfs_rq->tg);
+}
static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
{
@@ -3313,6 +3338,9 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
if (cfs_rq->avg.runnable_sum)
return false;
+ if (child_cfs_rq_on_list(cfs_rq))
+ return false;
+
return true;
}