Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 9 Sep 2021 16:04:02 +0200 | Subject | Re: [RFC PATCH v2 5/5] sched/fair: Simplify ancestor enqueue loops |
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On Thu, 19 Aug 2021 at 19:50, Michal Koutný <mkoutny@suse.com> wrote: > > When a task is enqueued or cfs_rq is unthrottled we have work to do from > the cfs_rq in question possibly up to root. The important nodes on the > path are throttled cfs_rqs or cfs_rqs already enqueud to their parent. > > Instead of multiple (interrupted) loops make all work in a single loop > and decide what all needs to be done inside it. This undoes parts of
These multiple break loops have been done to make unthrottle_cfs_rq, throttle_cfs_rq, enqueue_task_fair and dequeue_task_fair to follow the same pattern and I don't see any good reason to break this
> commit 39f23ce07b93 ("sched/fair: Fix unthrottle_cfs_rq() for > leaf_cfs_rq list") but it should not bring any functional changes. > > Note some PELT stats update code is duplicated both in enqueue_entity > and the ancestor loop (update_load_avg, se_update_runnable, > update_cfs_group). It'd be nice to factor these out, however, the later > parts of enqueue_entity rely on the updates, so stick with the current > repetition. > > Signed-off-by: Michal Koutný <mkoutny@suse.com> > --- > kernel/sched/fair.c | 57 +++++++++++++++++---------------------------- > 1 file changed, 21 insertions(+), 36 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 9978485334ec..79f183336fa8 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4883,6 +4883,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq) > struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg); > struct sched_entity *se; > long task_delta, idle_task_delta; > + int enqueue = 1; > > cfs_rq->throttled = 0; > > @@ -4911,29 +4912,21 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq) > task_delta = cfs_rq->h_nr_running; > idle_task_delta = cfs_rq->idle_h_nr_running; > for_each_sched_entity(se) { > - if (se->on_rq) > - break; > cfs_rq = cfs_rq_of(se); > - enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP); > - > - cfs_rq->h_nr_running += task_delta; > - cfs_rq->idle_h_nr_running += idle_task_delta; > > - /* end evaluation on encountering a throttled cfs_rq */ > - if (cfs_rq_throttled(cfs_rq)) > - goto unthrottle_throttle; > - } > - > - for_each_sched_entity(se) { > - cfs_rq = cfs_rq_of(se); > - > - update_load_avg(cfs_rq, se, UPDATE_TG); > - se_update_runnable(se); > + if (se->on_rq) > + enqueue = 0; > + if (enqueue) > + enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP); > + else { > + update_load_avg(cfs_rq, se, UPDATE_TG); > + se_update_runnable(se); > + /* XXX: no update_cfs_group(se); */ > + } > > cfs_rq->h_nr_running += task_delta; > cfs_rq->idle_h_nr_running += idle_task_delta; > > - > /* end evaluation on encountering a throttled cfs_rq */ > if (cfs_rq_throttled(cfs_rq)) > goto unthrottle_throttle; > @@ -5537,6 +5530,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > struct sched_entity *se = &p->se; > int idle_h_nr_running = task_has_idle_policy(p); > int task_new = !(flags & ENQUEUE_WAKEUP); > + int enqueue = 1; > > /* > * The code below (indirectly) updates schedutil which looks at > @@ -5555,27 +5549,18 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT); > > for_each_sched_entity(se) { > - if (se->on_rq) > - break; > cfs_rq = cfs_rq_of(se); > - enqueue_entity(cfs_rq, se, flags); > > - cfs_rq->h_nr_running++; > - cfs_rq->idle_h_nr_running += idle_h_nr_running; > - > - /* end evaluation on encountering a throttled cfs_rq */ > - if (cfs_rq_throttled(cfs_rq)) > - goto enqueue_throttle; > - > - flags = ENQUEUE_WAKEUP; > - } > - > - for_each_sched_entity(se) { > - cfs_rq = cfs_rq_of(se); > - > - update_load_avg(cfs_rq, se, UPDATE_TG); > - se_update_runnable(se); > - update_cfs_group(se); > + if (se->on_rq) > + enqueue = 0; > + if (enqueue) { > + enqueue_entity(cfs_rq, se, flags); > + flags = ENQUEUE_WAKEUP; > + } else { > + update_load_avg(cfs_rq, se, UPDATE_TG); > + se_update_runnable(se); > + update_cfs_group(se); > + } > > cfs_rq->h_nr_running++; > cfs_rq->idle_h_nr_running += idle_h_nr_running; > -- > 2.32.0 >
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