Messages in this thread | | | Date | Fri, 22 Jul 2011 17:11:41 +0530 | From | Kamalesh Babulal <> | Subject | Re: [patch 11/18] sched: prevent interactions with throttled entities |
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* Paul Turner <pjt@google.com> [2011-07-21 09:43:36]:
> >From the perspective of load-balance and shares distribution, throttled > entities should be invisible. > > However, both of these operations work on 'active' lists and are not > inherently aware of what group hierarchies may be present. In some cases this > may be side-stepped (e.g. we could sideload via tg_load_down in load balance) > while in others (e.g. update_shares()) it is more difficult to compute without > incurring some O(n^2) costs. > > Instead, track hierarchicaal throttled state at time of transition. This > allows us to easily identify whether an entity belongs to a throttled hierarchy > and avoid incorrect interactions with it. > > Also, when an entity leaves a throttled hierarchy we need to advance its > time averaging for shares averaging so that the elapsed throttled time is not > considered as part of the cfs_rq's operation. > > We also use this information to prevent buddy interactions in the wakeup and > yield_to() paths. > > Signed-off-by: Paul Turner <pjt@google.com> > Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> > > --- > kernel/sched.c | 2 - > kernel/sched_fair.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++++---- > 2 files changed, 94 insertions(+), 7 deletions(-) > > Index: tip/kernel/sched_fair.c > =================================================================== > --- tip.orig/kernel/sched_fair.c > +++ tip/kernel/sched_fair.c > @@ -725,6 +725,8 @@ account_entity_dequeue(struct cfs_rq *cf > } > > #ifdef CONFIG_FAIR_GROUP_SCHED > +/* we need this in update_cfs_load and load-balance functions below */ > +static inline int throttled_hierarchy(struct cfs_rq *cfs_rq); > # ifdef CONFIG_SMP > static void update_cfs_rq_load_contribution(struct cfs_rq *cfs_rq, > int global_update) > @@ -747,7 +749,7 @@ static void update_cfs_load(struct cfs_r > u64 now, delta; > unsigned long load = cfs_rq->load.weight; > > - if (cfs_rq->tg == &root_task_group) > + if (cfs_rq->tg == &root_task_group || throttled_hierarchy(cfs_rq)) > return; > > now = rq_of(cfs_rq)->clock_task; > @@ -856,7 +858,7 @@ static void update_cfs_shares(struct cfs > > tg = cfs_rq->tg; > se = tg->se[cpu_of(rq_of(cfs_rq))]; > - if (!se) > + if (!se || throttled_hierarchy(cfs_rq)) > return; > #ifndef CONFIG_SMP > if (likely(se->load.weight == tg->shares)) > @@ -1425,6 +1427,65 @@ static inline int cfs_rq_throttled(struc > return cfs_rq->throttled; > } > > +/* check whether cfs_rq, or any parent, is throttled */ > +static inline int throttled_hierarchy(struct cfs_rq *cfs_rq) > +{ > + return cfs_rq->throttle_count; > +} > + > +/* > + * Ensure that neither of the group entities corresponding to src_cpu or > + * dest_cpu are members of a throttled hierarchy when performing group > + * load-balance operations. > + */ > +static inline int throttled_lb_pair(struct task_group *tg, > + int src_cpu, int dest_cpu) > +{ > + struct cfs_rq *src_cfs_rq, *dest_cfs_rq; > + > + src_cfs_rq = tg->cfs_rq[src_cpu]; > + dest_cfs_rq = tg->cfs_rq[dest_cpu]; > + > + return throttled_hierarchy(src_cfs_rq) || > + throttled_hierarchy(dest_cfs_rq); > +} > + > +/* updated child weight may affect parent so we have to do this bottom up */ > +static int tg_unthrottle_up(struct task_group *tg, void *data) > +{ > + struct rq *rq = data; > + struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)]; > + > + cfs_rq->throttle_count--; > +#ifdef CONFIG_SMP > + if (!cfs_rq->throttle_count) { > + u64 delta = rq->clock_task - cfs_rq->load_stamp; > + > + /* leaving throttled state, advance shares averaging windows */ > + cfs_rq->load_stamp += delta; > + cfs_rq->load_last += delta; > + > + /* update entity weight now that we are on_rq again */ > + update_cfs_shares(cfs_rq); > + } > +#endif > + > + return 0; > +} > + > +static int tg_throttle_down(struct task_group *tg, void *data) > +{ > + struct rq *rq = data; > + struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)]; > + > + /* group is entering throttled state, record last load */ > + if (!cfs_rq->throttle_count) > + update_cfs_load(cfs_rq, 0); > + cfs_rq->throttle_count++; > + > + return 0; > +} > + > static __used void throttle_cfs_rq(struct cfs_rq *cfs_rq) > { > struct rq *rq = rq_of(cfs_rq); > @@ -1435,7 +1496,9 @@ static __used void throttle_cfs_rq(struc > se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))]; > > /* account load preceding throttle */ > - update_cfs_load(cfs_rq, 0); > + rcu_read_lock(); > + walk_tg_tree_from(cfs_rq->tg, tg_throttle_down, tg_nop, (void *)rq); > + rcu_read_unlock(); > > task_delta = cfs_rq->h_nr_running; > for_each_sched_entity(se) { > @@ -1476,6 +1539,10 @@ static void unthrottle_cfs_rq(struct cfs > list_del_rcu(&cfs_rq->throttled_list); > raw_spin_unlock(&cfs_b->lock); > > + update_rq_clock(rq); > + /* update hierarchical throttle state */ > + walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq); > + > if (!cfs_rq->load.weight) > return; > > @@ -1620,6 +1687,17 @@ static inline int cfs_rq_throttled(struc > { > return 0; > } > + > +static inline int throttled_hierarchy(struct cfs_rq *cfs_rq) > +{ > + return 0; > +} > + > +static inline int throttled_lb_pair(struct task_group *tg, > + int src_cpu, int dest_cpu) > +{ > + return 0; > +} > #endif > > /************************************************** > @@ -2519,6 +2597,9 @@ move_one_task(struct rq *this_rq, int th > > for_each_leaf_cfs_rq(busiest, cfs_rq) { > list_for_each_entry_safe(p, n, &cfs_rq->tasks, se.group_node) { > + if (throttled_lb_pair(task_group(p), > + busiest->cpu, this_cpu)) > + break; > > if (!can_migrate_task(p, busiest, this_cpu, > sd, idle, &pinned)) > @@ -2630,8 +2711,13 @@ static void update_shares(int cpu) > struct rq *rq = cpu_rq(cpu); > > rcu_read_lock(); > - for_each_leaf_cfs_rq(rq, cfs_rq) > + for_each_leaf_cfs_rq(rq, cfs_rq) { > + /* throttled entities do not contribute to load */ > + if (throttled_hierarchy(cfs_rq)) > + continue; > + > update_shares_cpu(cfs_rq->tg, cpu); > + } > rcu_read_unlock(); > } > > @@ -2655,9 +2741,10 @@ load_balance_fair(struct rq *this_rq, in > u64 rem_load, moved_load; > > /* > - * empty group > + * empty group or part of a throttled hierarchy > */ > - if (!busiest_cfs_rq->task_weight) > + if (!busiest_cfs_rq->task_weight || > + throttled_lb_pair(tg, busiest_cpu, this_cpu))
tip commit 9763b67fb9f30 removes both tg and busiest_cpu from load_balance_fair.
> continue; > > rem_load = (u64)rem_load_move * busiest_weight; > Index: tip/kernel/sched.c > =================================================================== > --- tip.orig/kernel/sched.c > +++ tip/kernel/sched.c > @@ -399,7 +399,7 @@ struct cfs_rq { > u64 runtime_expires; > s64 runtime_remaining; > > - int throttled; > + int throttled, throttle_count; > struct list_head throttled_list; > #endif > #endif > >
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