Messages in this thread Patch in this message | | | From | Michal Koutný <> | Subject | [RFC PATCH v2 1/5] sched/fair: Add ancestors of unthrottled undecayed cfs_rq | Date | Thu, 19 Aug 2021 19:50:30 +0200 |
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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> --- kernel/sched/fair.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 44c452072a1b..2c41a9007928 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4898,8 +4898,16 @@ 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) + if (!cfs_rq->load.weight) { + /* Nothing to run but something to decay? Complete the branch */ + if (cfs_rq->on_list) + for_each_sched_entity(se) { + if (list_add_leaf_cfs_rq(group_cfs_rq(se))) + break; + } + assert_list_leaf_cfs_rq(rq); return; + } task_delta = cfs_rq->h_nr_running; idle_task_delta = cfs_rq->idle_h_nr_running; -- 2.32.0
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