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| author | Michal Koutný <mkoutny@suse.com> | 2021-09-17 17:30:37 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-10-07 07:53:16 +0200 |
| commit | fce08b03923ed829ee021f27c443d0fb5c8d2f7a (patch) | |
| tree | 7802dc4e6399e06f8377ceb462f624757c86fa89 /kernel | |
| parent | d42683c2b196b1cc9ecae2a45dc2e4041a0ddd35 (diff) | |
sched/fair: Add ancestors of unthrottled undecayed cfs_rq
[ Upstream commit 2630cde26711dab0d0b56a8be1616475be646d13 ]
Since commit a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to
list on unthrottle") we add cfs_rqs with no runnable tasks but not fully
decayed into the load (leaf) list. We may ignore adding some ancestors
and therefore breaking tmp_alone_branch invariant. This broke LTP test
cfs_bandwidth01 and it was partially fixed in commit fdaba61ef8a2
("sched/fair: Ensure that the CFS parent is added after unthrottling").
I noticed the named test still fails even with the fix (but with low
probability, 1 in ~1000 executions of the test). The reason is when
bailing out of unthrottle_cfs_rq early, we may miss adding ancestors of
the unthrottled cfs_rq, thus, not joining tmp_alone_branch properly.
Fix this by adding ancestors if we notice the unthrottled cfs_rq was
added to the load list.
Fixes: a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to list on unthrottle")
Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Odin Ugedal <odin@uged.al>
Link: https://lore.kernel.org/r/20210917153037.11176-1-mkoutny@suse.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/fair.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 30a6984a58f7..423ec671a306 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4898,8 +4898,12 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq) /* update hierarchical throttle state */ walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq); - if (!cfs_rq->load.weight) + /* Nothing to run but something to decay (on_list)? Complete the branch */ + if (!cfs_rq->load.weight) { + if (cfs_rq->on_list) + goto unthrottle_throttle; return; + } task_delta = cfs_rq->h_nr_running; idle_task_delta = cfs_rq->idle_h_nr_running; |