Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 9 Sep 2021 15:57:37 +0200 | Subject | Re: [RFC PATCH v2 1/5] sched/fair: Add ancestors of unthrottled undecayed cfs_rq |
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On Thu, 19 Aug 2021 at 19:50, Michal Koutný <mkoutny@suse.com> wrote: > > 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)
Could you use !cfs_rq_is decayed(cfs_rq) ?
> + for_each_sched_entity(se) { > + if (list_add_leaf_cfs_rq(group_cfs_rq(se))) > + break; > + } > + assert_list_leaf_cfs_rq(rq);
Instead of adding a loop here you should better jump to unthrottle_throttle ?
> return; > + } > > task_delta = cfs_rq->h_nr_running; > idle_task_delta = cfs_rq->idle_h_nr_running; > -- > 2.32.0 >
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