code / linux / torvalds / linux / 7b6ae471e5415bc2bf4384a83ccb4c21de7824c0 / . / kernel / sched / pelt.c

// 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 |