// SPDX-License-Identifier: GPL-2.0
/*
* Per Entity Load Tracking (PELT)
*
* Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <[email protected]>
*
* Interactivity improvements by Mike Galbraith
* (C) 2007 Mike Galbraith <[email protected]>
*
* Various enhancements by Dmitry Adamushko.
* (C) 2007 Dmitry Adamushko <[email protected]>
*
* Group scheduling enhancements by Srivatsa Vaddagiri
* Copyright IBM Corporation, 2007
* Author: Srivatsa Vaddagiri <[email protected]>
*
* Scaled math optimizations by Thomas Gleixner
* Copyright (C) 2007, Thomas Gleixner <[email protected]>
*
* 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 <[email protected]>
*/
/*
* 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 sched_balance_newidle() which calls
* sched_balance_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_HW_PRESSURE
/*
* hardware:
*
* 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 HW pressure is
* tracked through load_avg. This is because HW pressure signal is
* time weighted "delta" capacity unlike util_avg which is binary.
* "delta capacity" = actual capacity -
* capped capacity a cpu due to a HW event.
*/
int update_hw_load_avg(u64 now, struct rq *rq, u64 capacity)
{
if (___update_load_sum(now, &rq->avg_hw,
capacity,
capacity,
capacity)) {
___update_load_avg(&rq->avg_hw, 1);
trace_pelt_hw_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
/*
* Load avg and utiliztion metrics need to be updated periodically and before
* consumption. This function updates the metrics for all subsystems except for
* the fair class. @rq must be locked and have its clock updated.
*/
bool update_other_load_avgs(struct rq *rq)
{
u64 now = rq_clock_pelt(rq);
const struct sched_class *curr_class = rq->curr->sched_class;
unsigned long hw_pressure = arch_scale_hw_pressure(cpu_of(rq));
lockdep_assert_rq_held(rq);
/* hw_pressure doesn't care about invariance */
return update_rt_rq_load_avg(now, rq, curr_class == &rt_sched_class) |
update_dl_rq_load_avg(now, rq, curr_class == &dl_sched_class) |
update_hw_load_avg(rq_clock_task(rq), rq, hw_pressure) |
update_irq_load_avg(rq, 0);
}
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