Hi Sacha
On Mon, 21 Jun 2021 at 18:22, Vincent Guittot
<vincent.guit...@linaro.org> wrote:
>
> Le lundi 21 juin 2021 à 14:42:23 (+0200), Odin Ugedal a écrit :
> > Hi,
> >
> > Did some more research, and it looks like this is what happens:
> >
> > $ 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
> >
> >
> > The attached diff (based on
> > https://lore.kernel.org/lkml/20210518125202.78658-3-o...@uged.al/)
> > fixes the issue for me. Not the most elegant solution, but the
> > simplest one as of now, and to show what is wrong.
> >
> > Any thoughts Vincent?
>
>
> I would prefer that we use the reason of adding the cfs in the list instead.
>
> Something like the below should also fixed the problem. It is based on a
> proposal I made to Rik sometimes ago when he tried to flatten the rq:
> https://lore.kernel.org/lkml/20190906191237.27006-6-r...@surriel.com/
>
> This will ensure that a cfs is added in the list whenever one of its child
> is still in the list.
Could you confirm that this patch fixes the problem for you too ?
>
> ---
> kernel/sched/fair.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ea7de54cb022..e751061a9449 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3272,6 +3272,31 @@ static inline void cfs_rq_util_change(struct cfs_rq
> *cfs_rq, int flags)
>
> #ifdef CONFIG_SMP
> #ifdef CONFIG_FAIR_GROUP_SCHED
> +/*
> + * Because list_add_leaf_cfs_rq always places a child cfs_rq on the list
> + * immediately before a parent cfs_rq, and cfs_rqs are removed from the list
> + * bottom-up, we only have to test whether the cfs_rq before us on the list
> + * is our child.
> + * If cfs_rq is not on the list, test wether a child needs its to be added to
> + * connect a branch to the tree * (see list_add_leaf_cfs_rq() for details).
> + */
> +static inline bool child_cfs_rq_on_list(struct cfs_rq *cfs_rq)
> +{
> + struct cfs_rq *prev_cfs_rq;
> + struct list_head *prev;
> +
> + if (cfs_rq->on_list) {
> + prev = cfs_rq->leaf_cfs_rq_list.prev;
> + } else {
> + struct rq *rq = rq_of(cfs_rq);
> +
> + prev = rq->tmp_alone_branch;
> + }
> +
> + prev_cfs_rq = container_of(prev, struct cfs_rq, leaf_cfs_rq_list);
> +
> + return (prev_cfs_rq->tg->parent == cfs_rq->tg);
> +}
>
> static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
> {
> @@ -3287,6 +3312,9 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq
> *cfs_rq)
> if (cfs_rq->avg.runnable_sum)
> return false;
>
> + if (child_cfs_rq_on_list(cfs_rq))
> + return false;
> +
> return true;
> }
>
> --
> 2.17.1
>
>
>
> >
> > Thanks
> > Odin
> >
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index bfaa6e1f6067..aa32e9c29efd 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -376,7 +376,8 @@ static inline bool list_add_leaf_cfs_rq(struct
> > cfs_rq *cfs_rq)
> > return false;
> > }
> >
> > -static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
> > +/* Returns 1 if cfs_rq was present in the list and removed */
> > +static inline bool list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
> > {
> > if (cfs_rq->on_list) {
> > struct rq *rq = rq_of(cfs_rq);
> > @@ -393,7 +394,9 @@ static inline void list_del_leaf_cfs_rq(struct
> > cfs_rq *cfs_rq)
> >
> > list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
> > cfs_rq->on_list = 0;
> > + return 1;
> > }
> > + return 0;
> > }
> >
> > static inline void assert_list_leaf_cfs_rq(struct rq *rq)
> > @@ -3298,24 +3301,6 @@ static inline void cfs_rq_util_change(struct
> > cfs_rq *cfs_rq, int flags)
> >
> > #ifdef CONFIG_SMP
> > #ifdef CONFIG_FAIR_GROUP_SCHED
> > -
> > -static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
> > -{
> > - if (cfs_rq->load.weight)
> > - return false;
> > -
> > - if (cfs_rq->avg.load_sum)
> > - return false;
> > -
> > - if (cfs_rq->avg.util_sum)
> > - return false;
> > -
> > - if (cfs_rq->avg.runnable_sum)
> > - return false;
> > -
> > - return true;
> > -}
> > -
> > /**
> > * update_tg_load_avg - update the tg's load avg
> > * @cfs_rq: the cfs_rq whose avg changed
> > @@ -4109,11 +4094,6 @@ static inline void update_misfit_status(struct
> > task_struct *p, struct rq *rq)
> >
> > #else /* CONFIG_SMP */
> >
> > -static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
> > -{
> > - return true;
> > -}
> > -
> > #define UPDATE_TG 0x0
> > #define SKIP_AGE_LOAD 0x0
> > #define DO_ATTACH 0x0
> > @@ -4771,10 +4751,11 @@ static int tg_unthrottle_up(struct task_group
> > *tg, void *data)
> > if (!cfs_rq->throttle_count) {
> > cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
> > cfs_rq->throttled_clock_task;
> > -
> > - /* Add cfs_rq with load or one or more already running
> > entities to the list */
> > - if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running)
> > + if (cfs_rq->insert_on_unthrottle) {
> > list_add_leaf_cfs_rq(cfs_rq);
> > + if (tg->parent)
> > +
> > tg->parent->cfs_rq[cpu_of(rq)]->insert_on_unthrottle = true;
> > + }
> > }
> >
> > return 0;
> > @@ -4788,7 +4769,7 @@ static int tg_throttle_down(struct task_group
> > *tg, void *data)
> > /* group is entering throttled state, stop time */
> > if (!cfs_rq->throttle_count) {
> > cfs_rq->throttled_clock_task = rq_clock_task(rq);
> > - list_del_leaf_cfs_rq(cfs_rq);
> > + cfs_rq->insert_on_unthrottle = list_del_leaf_cfs_rq(cfs_rq);
> > }
> > cfs_rq->throttle_count++;
> >
> > @@ -8019,6 +8000,23 @@ static bool __update_blocked_others(struct rq
> > *rq, bool *done)
> >
> > #ifdef CONFIG_FAIR_GROUP_SCHED
> >
> > +static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
> > +{
> > + if (cfs_rq->load.weight)
> > + return false;
> > +
> > + if (cfs_rq->avg.load_sum)
> > + return false;
> > +
> > + if (cfs_rq->avg.util_sum)
> > + return false;
> > +
> > + if (cfs_rq->avg.runnable_sum)
> > + return false;
> > +
> > + return true;
> > +}
> > +
> > static bool __update_blocked_fair(struct rq *rq, bool *done)
> > {
> > struct cfs_rq *cfs_rq, *pos;
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index a189bec13729..12a707d99ee6 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -602,6 +602,7 @@ struct cfs_rq {
> > u64 throttled_clock_task_time;
> > int throttled;
> > int throttle_count;
> > + int insert_on_unthrottle;
> > struct list_head throttled_list;
> > #endif /* CONFIG_CFS_BANDWIDTH */
> > #endif /* CONFIG_FAIR_GROUP_SCHED */
