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sched/pelt: Move PELT related code in a dedicated file
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We want to track rt_rq's utilization as a part of the estimation of the
whole rq's utilization. This is necessary because rt tasks can steal
utilization to cfs tasks and make them lighter than they are.
As we want to use the same load tracking mecanism for both and prevent
useless dependency between cfs and rt code, PELT code is moved in a
dedicated file.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: claudio@evidence.eu.com
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: joel@joelfernandes.org
Cc: juri.lelli@redhat.com
Cc: luca.abeni@santannapisa.it
Cc: patrick.bellasi@arm.com
Cc: quentin.perret@arm.com
Cc: rjw@rjwysocki.net
Cc: valentin.schneider@arm.com
Cc: viresh.kumar@linaro.org
Link: http://lkml.kernel.org/r/1530200714-4504-2-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Vincent Guittot authored and Ingo Molnar committed Jul 15, 2018
1 parent 8fe5c5a commit c079629
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Showing 5 changed files with 375 additions and 333 deletions.
2 changes: 1 addition & 1 deletion kernel/sched/Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@ obj-y += core.o loadavg.o clock.o cputime.o
obj-y += idle.o fair.o rt.o deadline.o
obj-y += wait.o wait_bit.o swait.o completion.o

obj-$(CONFIG_SMP) += cpupri.o cpudeadline.o topology.o stop_task.o
obj-$(CONFIG_SMP) += cpupri.o cpudeadline.o topology.o stop_task.o pelt.o
obj-$(CONFIG_SCHED_AUTOGROUP) += autogroup.o
obj-$(CONFIG_SCHEDSTATS) += stats.o
obj-$(CONFIG_SCHED_DEBUG) += debug.o
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333 changes: 1 addition & 332 deletions kernel/sched/fair.c
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Original file line number Diff line number Diff line change
Expand Up @@ -255,9 +255,6 @@ static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
return cfs_rq->rq;
}

/* An entity is a task if it doesn't "own" a runqueue */
#define entity_is_task(se) (!se->my_q)

static inline struct task_struct *task_of(struct sched_entity *se)
{
SCHED_WARN_ON(!entity_is_task(se));
Expand Down Expand Up @@ -419,7 +416,6 @@ static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
return container_of(cfs_rq, struct rq, cfs);
}

#define entity_is_task(se) 1

#define for_each_sched_entity(se) \
for (; se; se = NULL)
Expand Down Expand Up @@ -692,7 +688,7 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
}

#ifdef CONFIG_SMP

#include "pelt.h"
#include "sched-pelt.h"

static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);
Expand Down Expand Up @@ -2751,19 +2747,6 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
} while (0)

#ifdef CONFIG_SMP
/*
* XXX we want to get rid of these helpers and use the full load resolution.
*/
static inline long se_weight(struct sched_entity *se)
{
return scale_load_down(se->load.weight);
}

static inline long se_runnable(struct sched_entity *se)
{
return scale_load_down(se->runnable_weight);
}

static inline void
enqueue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
Expand Down Expand Up @@ -3064,314 +3047,6 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
}

#ifdef CONFIG_SMP
/*
* 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, int cpu, struct sched_avg *sa,
unsigned long load, unsigned long runnable, int running)
{
unsigned long scale_freq, scale_cpu;
u32 contrib = (u32)delta; /* p == 0 -> delta < 1024 */
u64 periods;

scale_freq = arch_scale_freq_capacity(cpu);
scale_cpu = arch_scale_cpu_capacity(NULL, cpu);

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_load_sum =
decay_load(sa->runnable_load_sum, periods);
sa->util_sum = decay_load((u64)(sa->util_sum), periods);

/*
* Step 2
*/
delta %= 1024;
contrib = __accumulate_pelt_segments(periods,
1024 - sa->period_contrib, delta);
}
sa->period_contrib = delta;

contrib = cap_scale(contrib, scale_freq);
if (load)
sa->load_sum += load * contrib;
if (runnable)
sa->runnable_load_sum += runnable * contrib;
if (running)
sa->util_sum += contrib * scale_cpu;

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, int cpu, 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()
*/
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, cpu, sa, load, runnable, running))
return 0;

return 1;
}

static __always_inline void
___update_load_avg(struct sched_avg *sa, unsigned long load, unsigned long runnable)
{
u32 divider = LOAD_AVG_MAX - 1024 + sa->period_contrib;

/*
* Step 2: update *_avg.
*/
sa->load_avg = div_u64(load * sa->load_sum, divider);
sa->runnable_load_avg = div_u64(runnable * sa->runnable_load_sum, divider);
sa->util_avg = sa->util_sum / divider;
}

/*
* When a task is dequeued, its estimated utilization should not be update if
* its util_avg has not been updated at least once.
* This flag is used to synchronize util_avg updates with util_est updates.
* We map this information into the LSB bit of the utilization saved at
* dequeue time (i.e. util_est.dequeued).
*/
#define UTIL_AVG_UNCHANGED 0x1

static inline void cfs_se_util_change(struct sched_avg *avg)
{
unsigned int enqueued;

if (!sched_feat(UTIL_EST))
return;

/* Avoid store if the flag has been already set */
enqueued = avg->util_est.enqueued;
if (!(enqueued & UTIL_AVG_UNCHANGED))
return;

/* Reset flag to report util_avg has been updated */
enqueued &= ~UTIL_AVG_UNCHANGED;
WRITE_ONCE(avg->util_est.enqueued, enqueued);
}

/*
* sched_entity:
*
* task:
* se_runnable() == se_weight()
*
* group: [ see update_cfs_group() ]
* se_weight() = tg->weight * grq->load_avg / tg->load_avg
* se_runnable() = se_weight(se) * grq->runnable_load_avg / grq->load_avg
*
* load_sum := runnable_sum
* load_avg = se_weight(se) * runnable_avg
*
* runnable_load_sum := runnable_sum
* runnable_load_avg = se_runnable(se) * runnable_avg
*
* XXX collapse load_sum and runnable_load_sum
*
* cfq_rs:
*
* load_sum = \Sum se_weight(se) * se->avg.load_sum
* load_avg = \Sum se->avg.load_avg
*
* runnable_load_sum = \Sum se_runnable(se) * se->avg.runnable_load_sum
* runnable_load_avg = \Sum se->avg.runable_load_avg
*/

static int
__update_load_avg_blocked_se(u64 now, int cpu, struct sched_entity *se)
{
if (entity_is_task(se))
se->runnable_weight = se->load.weight;

if (___update_load_sum(now, cpu, &se->avg, 0, 0, 0)) {
___update_load_avg(&se->avg, se_weight(se), se_runnable(se));
return 1;
}

return 0;
}

static int
__update_load_avg_se(u64 now, int cpu, struct cfs_rq *cfs_rq, struct sched_entity *se)
{
if (entity_is_task(se))
se->runnable_weight = se->load.weight;

if (___update_load_sum(now, cpu, &se->avg, !!se->on_rq, !!se->on_rq,
cfs_rq->curr == se)) {

___update_load_avg(&se->avg, se_weight(se), se_runnable(se));
cfs_se_util_change(&se->avg);
return 1;
}

return 0;
}

static int
__update_load_avg_cfs_rq(u64 now, int cpu, struct cfs_rq *cfs_rq)
{
if (___update_load_sum(now, cpu, &cfs_rq->avg,
scale_load_down(cfs_rq->load.weight),
scale_load_down(cfs_rq->runnable_weight),
cfs_rq->curr != NULL)) {

___update_load_avg(&cfs_rq->avg, 1, 1);
return 1;
}

return 0;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
/**
* update_tg_load_avg - update the tg's load avg
Expand Down Expand Up @@ -4039,12 +3714,6 @@ util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep)

#else /* CONFIG_SMP */

static inline int
update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
{
return 0;
}

#define UPDATE_TG 0x0
#define SKIP_AGE_LOAD 0x0
#define DO_ATTACH 0x0
Expand Down
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