When a task moves from/to a cfs_rq, we set a flag which is then used to propagate the change at parent level (sched_entity and cfs_rq) during next update. If the cfs_rq is throttled, the flag will stay pending until the cfs_rw is unthrottled.
For propagating the utilization, we copy the utilization of group cfs_rq to the sched_entity.
For propagating the load, we have to take into account the load of the whole task group in order to evaluate the load of the sched_entity. Similarly to what was done before the rewrite of PELT, we add a correction factor in case the task group's load is greater than its share so it will contribute the same load of a task of equal weight.
Signed-off-by: Vincent Guittot vincent.guittot@linaro.org --- kernel/sched/fair.c | 200 ++++++++++++++++++++++++++++++++++++++++++++++++++- kernel/sched/sched.h | 1 + 2 files changed, 200 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 625e7f7..8ba500f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3021,6 +3021,162 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq) }
/* + * Signed add and clamp on underflow. + * + * Explicitly do a load-store to ensure the intermediate value never hits + * memory. This allows lockless observations without ever seeing the negative + * values. + */ +#define add_positive(_ptr, _val) do { \ + typeof(_ptr) ptr = (_ptr); \ + typeof(_val) res, val = (_val); \ + typeof(*ptr) var = READ_ONCE(*ptr); \ + res = var + val; \ + if (res < 0) \ + res = 0; \ + WRITE_ONCE(*ptr, res); \ +} while (0) + +#ifdef CONFIG_FAIR_GROUP_SCHED +/* Take into account change of utilization of a child task group */ +static inline void +update_tg_cfs_util(struct cfs_rq *cfs_rq, struct sched_entity *se) +{ + struct cfs_rq *gcfs_rq = group_cfs_rq(se); + long delta = gcfs_rq->avg.util_avg - se->avg.util_avg; + + /* Nothing to update */ + if (!delta) + return; + + /* Set new sched_entity's utilization */ + se->avg.util_avg = gcfs_rq->avg.util_avg; + se->avg.util_sum = se->avg.util_avg * LOAD_AVG_MAX; + + /* Update parent cfs_rq utilization */ + add_positive(&cfs_rq->avg.util_avg, delta); + cfs_rq->avg.util_sum = cfs_rq->avg.util_avg * LOAD_AVG_MAX; +} + +/* Take into account change of load of a child task group */ +static inline void +update_tg_cfs_load(struct cfs_rq *cfs_rq, struct sched_entity *se) +{ + struct cfs_rq *gcfs_rq = group_cfs_rq(se); + long delta, load = gcfs_rq->avg.load_avg; + + /* + * If the load of group cfs_rq is null, the load of the + * sched_entity will also be null so we can skip the formula + */ + if (load) { + long tg_load; + + /* Get tg's load and ensure tg_load > 0 */ + tg_load = atomic_long_read(&gcfs_rq->tg->load_avg) + 1; + + /* Ensure tg_load >= load and updated with current load*/ + tg_load -= gcfs_rq->tg_load_avg_contrib; + tg_load += load; + + /* + * We need to compute a correction term in the case that the + * task group is consuming more cpu than a task of equal + * weight. A task with a weight equals to tg->shares will have + * a load less or equal to scale_load_down(tg->shares). + * Similarly, the sched_entities that represent the task group + * at parent level, can't have a load higher than + * scale_load_down(tg->shares). And the Sum of sched_entities' + * load must be <= scale_load_down(tg->shares). + */ + if (tg_load > scale_load_down(gcfs_rq->tg->shares)) { + /* scale gcfs_rq's load into tg's shares*/ + load *= scale_load_down(gcfs_rq->tg->shares); + load /= tg_load; + } + } + + delta = load - se->avg.load_avg; + + /* Nothing to update */ + if (!delta) + return; + + /* Set new sched_entity's load */ + se->avg.load_avg = load; + se->avg.load_sum = se->avg.load_avg * LOAD_AVG_MAX; + + /* Update parent cfs_rq load */ + add_positive(&cfs_rq->avg.load_avg, delta); + cfs_rq->avg.load_sum = cfs_rq->avg.load_avg * LOAD_AVG_MAX; + + /* + * If the sched_entity is already enqueued, we also have to update the + * runnable load avg. + */ + if (se->on_rq) { + /* Update parent cfs_rq runnable_load_avg */ + add_positive(&cfs_rq->runnable_load_avg, delta); + cfs_rq->runnable_load_sum = cfs_rq->runnable_load_avg * LOAD_AVG_MAX; + } +} + +static inline void set_tg_cfs_propagate(struct cfs_rq *cfs_rq) +{ + /* set cfs_rq's flag */ + cfs_rq->propagate_avg = 1; +} + +static inline int test_and_clear_tg_cfs_propagate(struct sched_entity *se) +{ + /* Get my cfs_rq */ + struct cfs_rq *cfs_rq = group_cfs_rq(se); + + /* Nothing to propagate */ + if (!cfs_rq->propagate_avg) + return 0; + + /* Clear my cfs_rq's flag */ + cfs_rq->propagate_avg = 0; + + return 1; +} + +/* Update task and its cfs_rq load average */ +static inline int propagate_entity_load_avg(struct sched_entity *se) +{ + struct cfs_rq *cfs_rq; + + if (entity_is_task(se)) + return 0; + + if (!test_and_clear_tg_cfs_propagate(se)) + return 0; + + /* Get parent cfs_rq */ + cfs_rq = cfs_rq_of(se); + + /* Propagate to parent */ + set_tg_cfs_propagate(cfs_rq); + + /* Update utilization */ + update_tg_cfs_util(cfs_rq, se); + + /* Update load */ + update_tg_cfs_load(cfs_rq, se); + + return 1; +} +#else +static inline int propagate_entity_load_avg(struct sched_entity *se) +{ + return 0; +} + +static inline void set_tg_cfs_propagate(struct cfs_rq *cfs_rq) {} +#endif + +/* * Unsigned subtract and clamp on underflow. * * Explicitly do a load-store to ensure the intermediate value never hits @@ -3101,6 +3257,7 @@ static inline void update_load_avg(struct sched_entity *se, int flags) u64 now = cfs_rq_clock_task(cfs_rq); struct rq *rq = rq_of(cfs_rq); int cpu = cpu_of(rq); + int decayed;
/* * Track task load average for carrying it to new CPU after migrated, and @@ -3111,7 +3268,11 @@ static inline void update_load_avg(struct sched_entity *se, int flags) se->on_rq * scale_load_down(se->load.weight), cfs_rq->curr == se, NULL);
- if (update_cfs_rq_load_avg(now, cfs_rq, true) && (flags & UPDATE_TG)) + decayed = update_cfs_rq_load_avg(now, cfs_rq, true); + + decayed |= propagate_entity_load_avg(se); + + if (decayed && (flags & UPDATE_TG)) update_tg_load_avg(cfs_rq, 0); }
@@ -3130,6 +3291,7 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s cfs_rq->avg.load_sum += se->avg.load_sum; cfs_rq->avg.util_avg += se->avg.util_avg; cfs_rq->avg.util_sum += se->avg.util_sum; + set_tg_cfs_propagate(cfs_rq);
cfs_rq_util_change(cfs_rq); } @@ -3149,6 +3311,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s sub_positive(&cfs_rq->avg.load_sum, se->avg.load_sum); sub_positive(&cfs_rq->avg.util_avg, se->avg.util_avg); sub_positive(&cfs_rq->avg.util_sum, se->avg.util_sum); + set_tg_cfs_propagate(cfs_rq);
cfs_rq_util_change(cfs_rq); } @@ -8509,6 +8672,22 @@ static void detach_task_cfs_rq(struct task_struct *p) update_load_avg(se, 0); detach_entity_load_avg(cfs_rq, se); update_tg_load_avg(cfs_rq, false); + +#ifdef CONFIG_FAIR_GROUP_SCHED + /* + * Propagate the detach across the tg tree to make it visible to the + * root + */ + se = se->parent; + for_each_sched_entity(se) { + cfs_rq = cfs_rq_of(se); + + if (cfs_rq_throttled(cfs_rq)) + break; + + update_load_avg(se, UPDATE_TG); + } +#endif }
static void attach_entity_cfs_rq(struct sched_entity *se) @@ -8527,6 +8706,22 @@ static void attach_entity_cfs_rq(struct sched_entity *se) update_load_avg(se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD); attach_entity_load_avg(cfs_rq, se); update_tg_load_avg(cfs_rq, false); + +#ifdef CONFIG_FAIR_GROUP_SCHED + /* + * Propagate the attach across the tg tree to make it visible to the + * root + */ + se = se->parent; + for_each_sched_entity(se) { + cfs_rq = cfs_rq_of(se); + + if (cfs_rq_throttled(cfs_rq)) + break; + + update_load_avg(se, UPDATE_TG); + } +#endif }
static void attach_task_cfs_rq(struct task_struct *p) @@ -8588,6 +8783,9 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime; #endif #ifdef CONFIG_SMP +#ifdef CONFIG_FAIR_GROUP_SCHED + cfs_rq->propagate_avg = 0; +#endif atomic_long_set(&cfs_rq->removed_load_avg, 0); atomic_long_set(&cfs_rq->removed_util_avg, 0); #endif diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 483616a..0517a9e 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -397,6 +397,7 @@ struct cfs_rq { unsigned long runnable_load_avg; #ifdef CONFIG_FAIR_GROUP_SCHED unsigned long tg_load_avg_contrib; + unsigned long propagate_avg; #endif atomic_long_t removed_load_avg, removed_util_avg; #ifndef CONFIG_64BIT