diff options
Diffstat (limited to 'kernel/sched/fair.c')
| -rw-r--r-- | kernel/sched/fair.c | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6b800a14b990..16d67f9b6955 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -971,6 +971,126 @@ static inline void update_entity_shares_tick(struct cfs_rq *cfs_rq) } #endif /* CONFIG_FAIR_GROUP_SCHED */ +#ifdef CONFIG_SMP +/* + * Approximate: + * val * y^n, where y^32 ~= 0.5 (~1 scheduling period) + */ +static __always_inline u64 decay_load(u64 val, u64 n) +{ + for (; n && val; n--) { + val *= 4008; + val >>= 12; + } + + return val; +} + +/* + * We can represent the historical contribution to runnable average as the + * coefficients of a geometric series. To do this we sub-divide our runnable + * history into segments of approximately 1ms (1024us); label the segment that + * occurred N-ms ago p_N, with p_0 corresponding to the current period, e.g. + * + * [<- 1024us ->|<- 1024us ->|<- 1024us ->| ... + * p0 p1 p2 + * (now) (~1ms ago) (~2ms ago) + * + * Let u_i denote the fraction of p_i that the entity was runnable. + * + * We then designate the fractions u_i as our co-efficients, yielding the + * following representation of historical load: + * u_0 + u_1*y + u_2*y^2 + u_3*y^3 + ... + * + * We choose y based on the with of a reasonably scheduling period, fixing: + * y^32 = 0.5 + * + * This means that the contribution to load ~32ms ago (u_32) will be weighted + * approximately half as much as the contribution to load within the last ms + * (u_0). + * + * When a period "rolls over" and we have new u_0`, multiplying the previous + * sum again by y is sufficient to update: + * load_avg = u_0` + y*(u_0 + u_1*y + u_2*y^2 + ... ) + * = u_0 + u_1*y + u_2*y^2 + ... [re-labeling u_i --> u_{i+1}] + */ +static __always_inline int __update_entity_runnable_avg(u64 now, + struct sched_avg *sa, + int runnable) +{ + u64 delta; + int delta_w, decayed = 0; + + delta = now - sa->last_runnable_update; + /* + * This should only happen when time goes backwards, which it + * unfortunately does during sched clock init when we swap over to TSC. + */ + if ((s64)delta < 0) { + sa->last_runnable_update = now; + return 0; + } + + /* + * Use 1024ns as the unit of measurement since it's a reasonable + * approximation of 1us and fast to compute. + */ + delta >>= 10; + if (!delta) + return 0; + sa->last_runnable_update = now; + + /* delta_w is the amount already accumulated against our next period */ + delta_w = sa->runnable_avg_period % 1024; + if (delta + delta_w >= 1024) { + /* period roll-over */ + decayed = 1; + + /* + * Now that we know we're crossing a period boundary, figure + * out how much from delta we need to complete the current + * period and accrue it. + */ + delta_w = 1024 - delta_w; + BUG_ON(delta_w > delta); + do { + if (runnable) + sa->runnable_avg_sum += delta_w; + sa->runnable_avg_period += delta_w; + + /* + * Remainder of delta initiates a new period, roll over + * the previous. + */ + sa->runnable_avg_sum = + decay_load(sa->runnable_avg_sum, 1); + sa->runnable_avg_period = + decay_load(sa->runnable_avg_period, 1); + + delta -= delta_w; + /* New period is empty */ + delta_w = 1024; + } while (delta >= 1024); + } + + /* Remainder of delta accrued against u_0` */ + if (runnable) + sa->runnable_avg_sum += delta; + sa->runnable_avg_period += delta; + + return decayed; +} + +/* Update a sched_entity's runnable average */ +static inline void update_entity_load_avg(struct sched_entity *se) +{ + __update_entity_runnable_avg(rq_of(cfs_rq_of(se))->clock_task, &se->avg, + se->on_rq); +} +#else +static inline void update_entity_load_avg(struct sched_entity *se) {} +#endif + static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se) { #ifdef CONFIG_SCHEDSTATS @@ -1097,6 +1217,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) */ update_curr(cfs_rq); update_cfs_load(cfs_rq, 0); + update_entity_load_avg(se); account_entity_enqueue(cfs_rq, se); update_cfs_shares(cfs_rq); @@ -1171,6 +1292,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) * Update run-time statistics of the 'current'. */ update_curr(cfs_rq); + update_entity_load_avg(se); update_stats_dequeue(cfs_rq, se); if (flags & DEQUEUE_SLEEP) { @@ -1340,6 +1462,8 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev) update_stats_wait_start(cfs_rq, prev); /* Put 'current' back into the tree. */ __enqueue_entity(cfs_rq, prev); + /* in !on_rq case, update occurred at dequeue */ + update_entity_load_avg(prev); } cfs_rq->curr = NULL; } @@ -1353,6 +1477,11 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued) update_curr(cfs_rq); /* + * Ensure that runnable average is periodically updated. + */ + update_entity_load_avg(curr); + + /* * Update share accounting for long-running entities. */ update_entity_shares_tick(cfs_rq); |