Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 15 Apr 2022 09:51:44 +0200 | Subject | Re: [External] Re: [PATCH] sched/fair: update tg->load_avg and se->load in throttle_cfs_rq() |
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On Fri, 15 Apr 2022 at 07:42, Chengming Zhou <zhouchengming@bytedance.com> wrote: > > On 2022/4/14 01:30, Benjamin Segall wrote: > > Chengming Zhou <zhouchengming@bytedance.com> writes: > > > >> We use update_load_avg(cfs_rq, se, 0) in throttle_cfs_rq(), so the > >> cfs_rq->tg_load_avg_contrib and task_group->load_avg won't be updated > >> even when the cfs_rq's load_avg has changed. > >> > >> And we also don't call update_cfs_group(se), so the se->load won't > >> be updated too. > >> > >> Change to use update_load_avg(cfs_rq, se, UPDATE_TG) and add > >> update_cfs_group(se) in throttle_cfs_rq(), like we do in > >> dequeue_task_fair(). > > > > Hmm, this does look more correct; Vincent, was having this not do > > UPDATE_TG deliberate, or an accident that we all missed when checking?
The cost of UPDATE_TG/update_tg_load_avg() is not free and the parent cfs->load_avg should not change because of the throttling but only the cfs->weight so I don't see a real benefit of UPDATE_TG.
Chengming, have you faced an issue or this change is based on code review ?
> > > > It looks like the unthrottle_cfs_rq side got UPDATE_TG added later in > > the two-loops pass, but not the throttle_cfs_rq side. > > Yes, UPDATE_TG was added in unthrottle_cfs_rq() in commit 39f23ce07b93 > ("sched/fair: Fix unthrottle_cfs_rq() for leaf_cfs_rq list"). > > > > > Also unthrottle_cfs_rq I'm guessing could still use update_cfs_group(se) > > It looks like we should also add update_cfs_group(se) in unthrottle_cfs_rq(). > > Thanks. > > > > > > >> > >> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> > >> --- > >> kernel/sched/fair.c | 3 ++- > >> 1 file changed, 2 insertions(+), 1 deletion(-) > >> > >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >> index d4bd299d67ab..b37dc1db7be7 100644 > >> --- a/kernel/sched/fair.c > >> +++ b/kernel/sched/fair.c > >> @@ -4936,8 +4936,9 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq) > >> if (!se->on_rq) > >> goto done; > >> > >> - update_load_avg(qcfs_rq, se, 0); > >> + update_load_avg(qcfs_rq, se, UPDATE_TG); > >> se_update_runnable(se); > >> + update_cfs_group(se); > >> > >> if (cfs_rq_is_idle(group_cfs_rq(se))) > >> idle_task_delta = cfs_rq->h_nr_running;
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