// SPDX-License-Identifier: GPL-2.0 /* * Per Entity Load Tracking * * Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> * * Interactivity improvements by Mike Galbraith * (C) 2007 Mike Galbraith <efault@gmx.de> * * Various enhancements by Dmitry Adamushko. * (C) 2007 Dmitry Adamushko <dmitry.adamushko@gmail.com> * * Group scheduling enhancements by Srivatsa Vaddagiri * Copyright IBM Corporation, 2007 * Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com> * * Scaled math optimizations by Thomas Gleixner * Copyright (C) 2007, Thomas Gleixner <tglx@linutronix.de> * * Adaptive scheduling granularity, math enhancements by Peter Zijlstra * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra * * Move PELT related code from fair.c into this pelt.c file * Author: Vincent Guittot <vincent.guittot@linaro.org> */ #include <linux/sched.h> #include "sched.h" #include "pelt.h" /* * Approximate: * val * y^n, where y^32 ~= 0.5 (~1 scheduling period) */ static u64 decay_load(u64 val, u64 n) { unsigned int local_n; if (unlikely(n > LOAD_AVG_PERIOD * 63)) return 0; /* after bounds checking we can collapse to 32-bit */ local_n = n; /* * As y^PERIOD = 1/2, we can combine * y^n = 1/2^(n/PERIOD) * y^(n%PERIOD) * With a look-up table which covers y^n (n<PERIOD) * * To achieve constant time decay_load. */ if (unlikely(local_n >= LOAD_AVG_PERIOD)) { val >>= local_n / LOAD_AVG_PERIOD; local_n %= LOAD_AVG_PERIOD; } val = mul_u64_u32_shr(val, runnable_avg_yN_inv[local_n], 32); return val; } static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3) { u32 c1, c2, c3 = d3; /* y^0 == 1 */ /* * c1 = d1 y^p */ c1 = decay_load((u64)d1, periods); /* * p-1 * c2 = 1024 \Sum y^n * n=1 * * inf inf * = 1024 ( \Sum y^n - \Sum y^n - y^0 ) * n=0 n=p */ c2 = LOAD_AVG_MAX - decay_load(LOAD_AVG_MAX, periods) - 1024; return c1 + c2 + c3; } /* * Accumulate the three separate parts of the sum; d1 the remainder * of the last (incomplete) period, d2 the span of full periods and d3 * the remainder of the (incomplete) current period. * * d1 d2 d3 * ^ ^ ^ * | | | * |<->|<----------------->|<--->| * ... |---x---|------| ... |------|-----x (now) * * p-1 * u' = (u + d1) y^p + 1024 \Sum y^n + d3 y^0 * n=1 * * = u y^p + (Step 1) * * p-1 * d1 y^p + 1024 \Sum y^n + d3 y^0 (Step 2) * n=1 */ static __always_inline u32 accumulate_sum(u64 delta, struct sched_avg *sa, unsigned long load, unsigned long runnable, int running) { u32 contrib = (u32)delta; /* p == 0 -> delta < 1024 */ u64 periods; delta += sa->period_contrib; periods = delta / 1024; /* A period is 1024us (~1ms) */ /* * Step 1: decay old *_sum if we crossed period boundaries. */ if (periods) { sa->load_sum = decay_load(sa->load_sum, periods); sa->runnable_sum = decay_load(sa->runnable_sum, periods); sa->util_sum = decay_load((u64)(sa->util_sum), periods); /* * Step 2 */ delta %= 1024; if (load) { /* * This relies on the: * * if (!load) * runnable = running = 0; * * clause from ___update_load_sum(); this results in * the below usage of @contrib to disappear entirely, * so no point in calculating it. */ contrib = __accumulate_pelt_segments(periods, 1024 - sa->period_contrib, delta); } } sa->period_contrib = delta; if (load) sa->load_sum += load * contrib; if (runnable) sa->runnable_sum += runnable * contrib << SCHED_CAPACITY_SHIFT; if (running) sa->util_sum += contrib << SCHED_CAPACITY_SHIFT; return periods; } /* * 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_load_sum(u64 now, struct sched_avg *sa, unsigned long load, unsigned long runnable, int running) { u64 delta; delta = now - sa->last_update_time; /* * 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_update_time = 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_update_time += delta << 10; /* * running is a subset of runnable (weight) so running can't be set if * runnable is clear. But there are some corner cases where the current * se has been already dequeued but cfs_rq->curr still points to it. * This means that weight will be 0 but not running for a sched_entity * but also for a cfs_rq if the latter becomes idle. As an example, * this happens during idle_balance() which calls * update_blocked_averages(). * * Also see the comment in accumulate_sum(). */ if (!load) runnable = running = 0; /* * Now we know we crossed measurement unit boundaries. The *_avg * accrues by two steps: * * Step 1: accumulate *_sum since last_update_time. If we haven't * crossed period boundaries, finish. */ if (!accumulate_sum(delta, sa, load, runnable, running)) return 0; return 1; } /* * When syncing *_avg with *_sum, we must take into account the current * position in the PELT segment otherwise the remaining part of the segment * will be considered as idle time whereas it's not yet elapsed and this will * generate unwanted oscillation in the range [1002..1024[. * * The max value of *_sum varies with the position in the time segment and is * equals to : * * LOAD_AVG_MAX*y + sa->period_contrib * * which can be simplified into: * * LOAD_AVG_MAX - 1024 + sa->period_contrib * * because LOAD_AVG_MAX*y == LOAD_AVG_MAX-1024 * * The same care must be taken when a sched entity is added, updated or * removed from a cfs_rq and we need to update sched_avg. Scheduler entities * and the cfs rq, to which they are attached, have the same position in the * time segment because they use the same clock. This means that we can use * the period_contrib of cfs_rq when updating the sched_avg of a sched_entity * if it's more convenient. */ static __always_inline void ___update_load_avg(struct sched_avg *sa, unsigned long load) { u32 divider = get_pelt_divider(sa); /* * Step 2: update *_avg. */ sa->load_avg = div_u64(load * sa->load_sum, divider); sa->runnable_avg = div_u64(sa->runnable_sum, divider); WRITE_ONCE(sa->util_avg, sa->util_sum / divider); } /* * sched_entity: * * task: * se_weight() = se->load.weight * se_runnable() = !!on_rq * * group: [ see update_cfs_group() ] * se_weight() = tg->weight * grq->load_avg / tg->load_avg * se_runnable() = grq->h_nr_running * * runnable_sum = se_runnable() * runnable = grq->runnable_sum * runnable_avg = runnable_sum * * load_sum := runnable * load_avg = se_weight(se) * load_sum * * cfq_rq: * * runnable_sum = \Sum se->avg.runnable_sum * runnable_avg = \Sum se->avg.runnable_avg * * load_sum = \Sum se_weight(se) * se->avg.load_sum * load_avg = \Sum se->avg.load_avg */ int __update_load_avg_blocked_se(u64 now, struct sched_entity *se) { if (___update_load_sum(now, &se->avg, 0, 0, 0)) { ___update_load_avg(&se->avg, se_weight(se)); trace_pelt_se_tp(se); return 1; } return 0; } int __update_load_avg_se(u64 now, struct cfs_rq *cfs_rq, struct sched_entity *se) { if (___update_load_sum(now, &se->avg, !!se->on_rq, se_runnable(se), cfs_rq->curr == se)) { ___update_load_avg(&se->avg, se_weight(se)); cfs_se_util_change(&se->avg); trace_pelt_se_tp(se); return 1; } return 0; } int __update_load_avg_cfs_rq(u64 now, struct cfs_rq *cfs_rq) { if (___update_load_sum(now, &cfs_rq->avg, scale_load_down(cfs_rq->load.weight), cfs_rq->h_nr_running, cfs_rq->curr != NULL)) { ___update_load_avg(&cfs_rq->avg, 1); trace_pelt_cfs_tp(cfs_rq); return 1; } return 0; } /* * rt_rq: * * util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked * util_sum = cpu_scale * load_sum * runnable_sum = util_sum * * load_avg and runnable_avg are not supported and meaningless. * */ int update_rt_rq_load_avg(u64 now, struct rq *rq, int running) { if (___update_load_sum(now, &rq->avg_rt, running, running, running)) { ___update_load_avg(&rq->avg_rt, 1); trace_pelt_rt_tp(rq); return 1; } return 0; } /* * dl_rq: * * util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked * util_sum = cpu_scale * load_sum * runnable_sum = util_sum * * load_avg and runnable_avg are not supported and meaningless. * */ int update_dl_rq_load_avg(u64 now, struct rq *rq, int running) { if (___update_load_sum(now, &rq->avg_dl, running, running, running)) { ___update_load_avg(&rq->avg_dl, 1); trace_pelt_dl_tp(rq); return 1; } return 0; } #ifdef CONFIG_SCHED_THERMAL_PRESSURE /* * thermal: * * load_sum = \Sum se->avg.load_sum but se->avg.load_sum is not tracked * * util_avg and runnable_load_avg are not supported and meaningless. * * Unlike rt/dl utilization tracking that track time spent by a cpu * running a rt/dl task through util_avg, the average thermal pressure is * tracked through load_avg. This is because thermal pressure signal is * time weighted "delta" capacity unlike util_avg which is binary. * "delta capacity" = actual capacity - * capped capacity a cpu due to a thermal event. */ int update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity) { if (___update_load_sum(now, &rq->avg_thermal, capacity, capacity, capacity)) { ___update_load_avg(&rq->avg_thermal, 1); trace_pelt_thermal_tp(rq); return 1; } return 0; } #endif #ifdef CONFIG_HAVE_SCHED_AVG_IRQ /* * irq: * * util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked * util_sum = cpu_scale * load_sum * runnable_sum = util_sum * * load_avg and runnable_avg are not supported and meaningless. * */ int update_irq_load_avg(struct rq *rq, u64 running) { int ret = 0; /* * We can't use clock_pelt because irq time is not accounted in * clock_task. Instead we directly scale the running time to * reflect the real amount of computation */ running = cap_scale(running, arch_scale_freq_capacity(cpu_of(rq))); running = cap_scale(running, arch_scale_cpu_capacity(cpu_of(rq))); /* * We know the time that has been used by interrupt since last update * but we don't when. Let be pessimistic and assume that interrupt has * happened just before the update. This is not so far from reality * because interrupt will most probably wake up task and trig an update * of rq clock during which the metric is updated. * We start to decay with normal context time and then we add the * interrupt context time. * We can safely remove running from rq->clock because * rq->clock += delta with delta >= running */ ret = ___update_load_sum(rq->clock - running, &rq->avg_irq, 0, 0, 0); ret += ___update_load_sum(rq->clock, &rq->avg_irq, 1, 1, 1); if (ret) { ___update_load_avg(&rq->avg_irq, 1); trace_pelt_irq_tp(rq); } return ret; } #endif