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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: a7b359fc6a
("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
This commit is contained in:
parent
a96bfed64c
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@ -3298,6 +3298,31 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
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#ifdef CONFIG_SMP
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#ifdef CONFIG_FAIR_GROUP_SCHED
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/*
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* Because list_add_leaf_cfs_rq always places a child cfs_rq on the list
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* immediately before a parent cfs_rq, and cfs_rqs are removed from the list
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* bottom-up, we only have to test whether the cfs_rq before us on the list
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* is our child.
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* If cfs_rq is not on the list, test whether a child needs its to be added to
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* connect a branch to the tree * (see list_add_leaf_cfs_rq() for details).
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*/
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static inline bool child_cfs_rq_on_list(struct cfs_rq *cfs_rq)
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{
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struct cfs_rq *prev_cfs_rq;
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struct list_head *prev;
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if (cfs_rq->on_list) {
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prev = cfs_rq->leaf_cfs_rq_list.prev;
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} else {
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struct rq *rq = rq_of(cfs_rq);
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prev = rq->tmp_alone_branch;
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}
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prev_cfs_rq = container_of(prev, struct cfs_rq, leaf_cfs_rq_list);
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return (prev_cfs_rq->tg->parent == cfs_rq->tg);
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}
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static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
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{
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@ -3313,6 +3338,9 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
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if (cfs_rq->avg.runnable_sum)
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return false;
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if (child_cfs_rq_on_list(cfs_rq))
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return false;
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return true;
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}
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