В Ср, 25/06/2014 в 11:53 +0400, Kirill Tkhai пишет: > В Вт, 24/06/2014 в 23:26 +0400, Kirill Tkhai пишет: > > On 24.06.2014 23:13, [email protected] wrote: > > > Kirill Tkhai <[email protected]> writes: > > > > > >> On 24.06.2014 21:03, [email protected] wrote: > > >>> Kirill Tkhai <[email protected]> writes: > > >>> > > >>>> We kill rq->rd on the CPU_DOWN_PREPARE stage: > > >>>> > > >>>> cpuset_cpu_inactive -> cpuset_update_active_cpus -> > > >>>> partition_sched_domains -> > > >>>> -> cpu_attach_domain -> rq_attach_root -> set_rq_offline > > >>>> > > >>>> This unthrottles all throttled cfs_rqs. > > >>>> > > >>>> But the cpu is still able to call schedule() till > > >>>> > > >>>> take_cpu_down->__cpu_disable() > > >>>> > > >>>> is called from stop_machine. > > >>>> > > >>>> This case the tasks from just unthrottled cfs_rqs are pickable > > >>>> in a standard scheduler way, and they are picked by dying cpu. > > >>>> The cfs_rqs becomes throttled again, and migrate_tasks() > > >>>> in migration_call skips their tasks (one more unthrottle > > >>>> in migrate_tasks()->CPU_DYING does not happen, because rq->rd > > >>>> is already NULL). > > >>>> > > >>>> Patch sets runtime_enabled to zero. This guarantees, the runtime > > >>>> is not accounted, and the cfs_rqs won't exceed given > > >>>> cfs_rq->runtime_remaining = 1, and tasks will be pickable > > >>>> in migrate_tasks(). runtime_enabled is recalculated again > > >>>> when rq becomes online again. > > >>>> > > >>>> Ben Segall also noticed, we always enable runtime in > > >>>> tg_set_cfs_bandwidth(). Actually, we should do that for online > > >>>> cpus only. To fix that, we check if a cpu is online when > > >>>> its rq is locked. This guarantees we do not have races with > > >>>> set_rq_offline(), which also requires rq->lock. > > >>>> > > >>>> v2: Fix race with tg_set_cfs_bandwidth(). > > >>>> Move cfs_rq->runtime_enabled=0 above unthrottle_cfs_rq(). > > >>>> > > >>>> Signed-off-by: Kirill Tkhai <[email protected]> > > >>>> CC: Konstantin Khorenko <[email protected]> > > >>>> CC: Ben Segall <[email protected]> > > >>>> CC: Paul Turner <[email protected]> > > >>>> CC: Srikar Dronamraju <[email protected]> > > >>>> CC: Mike Galbraith <[email protected]> > > >>>> CC: Peter Zijlstra <[email protected]> > > >>>> CC: Ingo Molnar <[email protected]> > > >>>> --- > > >>>> kernel/sched/core.c | 15 +++++++++++---- > > >>>> kernel/sched/fair.c | 22 ++++++++++++++++++++++ > > >>>> 2 files changed, 33 insertions(+), 4 deletions(-) > > >>>> > > >>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > >>>> index 7f3063c..707a3c5 100644 > > >>>> --- a/kernel/sched/core.c > > >>>> +++ b/kernel/sched/core.c > > >>>> @@ -7842,11 +7842,18 @@ static int tg_set_cfs_bandwidth(struct > > >>>> task_group *tg, u64 period, u64 quota) > > >>>> struct rq *rq = cfs_rq->rq; > > >>>> > > >>>> raw_spin_lock_irq(&rq->lock); > > >>>> - cfs_rq->runtime_enabled = runtime_enabled; > > >>>> - cfs_rq->runtime_remaining = 0; > > >>>> + /* > > >>>> + * Do not enable runtime on offline runqueues. We > > >>>> specially > > >>>> + * make it disabled in unthrottle_offline_cfs_rqs(). > > >>>> + */ > > >>>> + if (cpu_online(i)) { > > >>>> + cfs_rq->runtime_enabled = runtime_enabled; > > >>>> + cfs_rq->runtime_remaining = 0; > > >>>> + > > >>>> + if (cfs_rq->throttled) > > >>>> + unthrottle_cfs_rq(cfs_rq); > > >>>> + } > > >>> > > >>> We can just do for_each_online_cpu, yes? Also we probably need > > >>> get_online_cpus/put_online_cpus, and/or want cpu_active_mask instead > > >>> right? > > >>> > > >> > > >> Yes, we can use for_each_online_cpu/for_each_active_cpu with > > >> get_online_cpus() taken. But it adds one more lock dependence. > > >> This looks worse for me. > > > > > > I mean, you need get_online_cpus anyway - cpu_online is just a test > > > against the same mask that for_each_online_cpu uses, and without taking > > > the lock you can still race with offlining and reset runtime_enabled. > > > > > > > Oh, I see. Thanks. > > But we can check for rq->online, don't we? How about this?
Oh, rq->online presents only in SMP case... Ok, lets do with get_online_cpus()... > > sched/fair: Disable runtime_enabled on dying rq > > We kill rq->rd on the CPU_DOWN_PREPARE stage: > > cpuset_cpu_inactive -> cpuset_update_active_cpus -> > partition_sched_domains -> > -> cpu_attach_domain -> rq_attach_root -> set_rq_offline > > This unthrottles all throttled cfs_rqs. > > But the cpu is still able to call schedule() till > > take_cpu_down->__cpu_disable() > > is called from stop_machine. > > This case the tasks from just unthrottled cfs_rqs are pickable > in a standard scheduler way, and they are picked by dying cpu. > The cfs_rqs becomes throttled again, and migrate_tasks() > in migration_call skips their tasks (one more unthrottle > in migrate_tasks()->CPU_DYING does not happen, because rq->rd > is already NULL). > > Patch sets runtime_enabled to zero. This guarantees, the runtime > is not accounted, and the cfs_rqs won't exceed given > cfs_rq->runtime_remaining = 1, and tasks will be pickable > in migrate_tasks(). runtime_enabled is recalculated again > when rq becomes online again. > > Ben Segall also noticed, we always enable runtime in > tg_set_cfs_bandwidth(). Actually, we should do that for online > cpus only. To fix that, we check if a cpu is online when > its rq is locked. This guarantees we do not have races with > set_rq_offline(), which also requires rq->lock. > > v2: Fix race with tg_set_cfs_bandwidth(). > Move cfs_rq->runtime_enabled=0 above unthrottle_cfs_rq(). > v3: Check for rq->online instead of cpu_active. > > Signed-off-by: Kirill Tkhai <[email protected]> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index ceea8d0..4c163c9 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -7837,11 +7837,17 @@ static int tg_set_cfs_bandwidth(struct task_group > *tg, u64 period, u64 quota) > struct rq *rq = cfs_rq->rq; > > raw_spin_lock_irq(&rq->lock); > - cfs_rq->runtime_enabled = runtime_enabled; > - cfs_rq->runtime_remaining = 0; > + /* > + * Do not enable runtime on offline runqueues. We specially > + * disable it in unthrottle_offline_cfs_rqs(). > + */ > + if (rq->online) { > + cfs_rq->runtime_enabled = runtime_enabled; > + cfs_rq->runtime_remaining = 0; > > - if (cfs_rq->throttled) > - unthrottle_cfs_rq(cfs_rq); > + if (cfs_rq->throttled) > + unthrottle_cfs_rq(cfs_rq); > + } > raw_spin_unlock_irq(&rq->lock); > } > if (runtime_was_enabled && !runtime_enabled) > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 1f9c457..5616d23 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -3776,6 +3776,19 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth > *cfs_b) > hrtimer_cancel(&cfs_b->slack_timer); > } > > +static void __maybe_unused update_runtime_enabled(struct rq *rq) > +{ > + struct cfs_rq *cfs_rq; > + > + for_each_leaf_cfs_rq(rq, cfs_rq) { > + struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth; > + > + raw_spin_lock(&cfs_b->lock); > + cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF; > + raw_spin_unlock(&cfs_b->lock); > + } > +} > + > static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq) > { > struct cfs_rq *cfs_rq; > @@ -3789,6 +3802,12 @@ static void __maybe_unused > unthrottle_offline_cfs_rqs(struct rq *rq) > * there's some valid quota amount > */ > cfs_rq->runtime_remaining = 1; > + /* > + * Offline rq is schedulable till cpu is completely disabled > + * in take_cpu_down(), so we prevent new cfs throttling here. > + */ > + cfs_rq->runtime_enabled = 0; > + > if (cfs_rq_throttled(cfs_rq)) > unthrottle_cfs_rq(cfs_rq); > } > @@ -3832,6 +3851,7 @@ static inline struct cfs_bandwidth > *tg_cfs_bandwidth(struct task_group *tg) > return NULL; > } > static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {} > +static inline void update_runtime_enabled(struct rq *rq) {} > static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {} > > #endif /* CONFIG_CFS_BANDWIDTH */ > @@ -7325,6 +7345,8 @@ void trigger_load_balance(struct rq *rq) > static void rq_online_fair(struct rq *rq) > { > update_sysctl(); > + > + update_runtime_enabled(rq); > } > > static void rq_offline_fair(struct rq *rq) > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
