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sched: Maintain the load contribution of blocked entities 

We are currently maintaining:

  runnable_load(cfs_rq) = \Sum task_load(t)

For all running children t of cfs_rq.  While this can be naturally updated for
tasks in a runnable state (as they are scheduled); this does not account for
the load contributed by blocked task entities.

This can be solved by introducing a separate accounting for blocked load:

  blocked_load(cfs_rq) = \Sum runnable(b) * weight(b)

Obviously we do not want to iterate over all blocked entities to account for
their decay, we instead observe that:

  runnable_load(t) = \Sum p_i*y^i

and that to account for an additional idle period we only need to compute:

  y*runnable_load(t).

This means that we can compute all blocked entities at once by evaluating:

  blocked_load(cfs_rq)` = y * blocked_load(cfs_rq)

Finally we maintain a decay counter so that when a sleeping entity re-awakens
we can determine how much of its load should be removed from the blocked sum.

Signed-off-by: Paul Turner <pjt@google.com>
Reviewed-by: Ben Segall <bsegall@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120823141506.585389902@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Paul Turner 2012-10-04 13:18:30 +02:00 committed by Ingo Molnar
parent 2dac754e10
commit 9ee474f556
5 changed files with 122 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/sched.h
View File

@ -1103,6 +1103,7 @@ struct sched_avg {
*/
u32 runnable_avg_sum, runnable_avg_period;
u64 last_runnable_update;
s64 decay_count;
unsigned long load_avg_contrib;
};

1
kernel/sched/core.c
View File

@ -1528,7 +1528,6 @@ static void __sched_fork(struct task_struct *p)
p->se.avg.runnable_avg_period = 0;
p->se.avg.runnable_avg_sum = 0;
#endif
#ifdef CONFIG_SCHEDSTATS
memset(&p->se.statistics, 0, sizeof(p->se.statistics));
#endif

3
kernel/sched/debug.c
View File

@ -95,6 +95,7 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group
P(se->avg.runnable_avg_sum);
P(se->avg.runnable_avg_period);
P(se->avg.load_avg_contrib);
P(se->avg.decay_count);
#endif
#undef PN
#undef P
@ -227,6 +228,8 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
atomic_read(&cfs_rq->tg->load_weight));
SEQ_printf(m, " .%-30s: %lld\n", "runnable_load_avg",
cfs_rq->runnable_load_avg);
SEQ_printf(m, " .%-30s: %lld\n", "blocked_load_avg",
cfs_rq->blocked_load_avg);
#endif
print_cfs_group_stats(m, cpu, cfs_rq->tg);

128
kernel/sched/fair.c
View File

@ -259,6 +259,8 @@ static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
return grp->my_q;
}
static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq);
static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
if (!cfs_rq->on_list) {
@ -278,6 +280,8 @@ static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
}
cfs_rq->on_list = 1;
/* We should have no load, but we need to update last_decay. */
update_cfs_rq_blocked_load(cfs_rq);
}
}
@ -1081,6 +1085,20 @@ static __always_inline int __update_entity_runnable_avg(u64 now,
return decayed;
}
/* Synchronize an entity's decay with its parenting cfs_rq.*/
static inline void __synchronize_entity_decay(struct sched_entity *se)
{
struct cfs_rq *cfs_rq = cfs_rq_of(se);
u64 decays = atomic64_read(&cfs_rq->decay_counter);
decays -= se->avg.decay_count;
if (!decays)
return;
se->avg.load_avg_contrib = decay_load(se->avg.load_avg_contrib, decays);
se->avg.decay_count = 0;
}
/* Compute the current contribution to load_avg by se, return any delta */
static long __update_entity_load_avg_contrib(struct sched_entity *se)
{
@ -1096,8 +1114,18 @@ static long __update_entity_load_avg_contrib(struct sched_entity *se)
return se->avg.load_avg_contrib - old_contrib;
}
static inline void subtract_blocked_load_contrib(struct cfs_rq *cfs_rq,
long load_contrib)
{
if (likely(load_contrib < cfs_rq->blocked_load_avg))
cfs_rq->blocked_load_avg -= load_contrib;
else
cfs_rq->blocked_load_avg = 0;
}
/* Update a sched_entity's runnable average */
static inline void update_entity_load_avg(struct sched_entity *se)
static inline void update_entity_load_avg(struct sched_entity *se,
int update_cfs_rq)
{
struct cfs_rq *cfs_rq = cfs_rq_of(se);
long contrib_delta;
@ -1107,8 +1135,34 @@ static inline void update_entity_load_avg(struct sched_entity *se)
return;
contrib_delta = __update_entity_load_avg_contrib(se);
if (!update_cfs_rq)
return;
if (se->on_rq)
cfs_rq->runnable_load_avg += contrib_delta;
else
subtract_blocked_load_contrib(cfs_rq, -contrib_delta);
}
/*
* Decay the load contributed by all blocked children and account this so that
* their contribution may appropriately discounted when they wake up.
*/
static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq)
{
u64 now = rq_of(cfs_rq)->clock_task >> 20;
u64 decays;
decays = now - cfs_rq->last_decay;
if (!decays)
return;
cfs_rq->blocked_load_avg = decay_load(cfs_rq->blocked_load_avg,
decays);
atomic64_add(decays, &cfs_rq->decay_counter);
cfs_rq->last_decay = now;
}
static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
@ -1118,26 +1172,53 @@ static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
/* Add the load generated by se into cfs_rq's child load-average */
static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
struct sched_entity *se)
struct sched_entity *se,
int wakeup)
{
update_entity_load_avg(se);
/* we track migrations using entity decay_count == 0 */
if (unlikely(!se->avg.decay_count)) {
se->avg.last_runnable_update = rq_of(cfs_rq)->clock_task;
wakeup = 0;
} else {
__synchronize_entity_decay(se);
}
if (wakeup)
subtract_blocked_load_contrib(cfs_rq, se->avg.load_avg_contrib);
update_entity_load_avg(se, 0);
cfs_rq->runnable_load_avg += se->avg.load_avg_contrib;
update_cfs_rq_blocked_load(cfs_rq);
}
/* Remove se's load from this cfs_rq child load-average */
/*
* Remove se's load from this cfs_rq child load-average, if the entity is
* transitioning to a blocked state we track its projected decay using
* blocked_load_avg.
*/
static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,
struct sched_entity *se)
struct sched_entity *se,
int sleep)
{
update_entity_load_avg(se);
update_entity_load_avg(se, 1);
cfs_rq->runnable_load_avg -= se->avg.load_avg_contrib;
if (sleep) {
cfs_rq->blocked_load_avg += se->avg.load_avg_contrib;
se->avg.decay_count = atomic64_read(&cfs_rq->decay_counter);
} /* migrations, e.g. sleep=0 leave decay_count == 0 */
}
#else
static inline void update_entity_load_avg(struct sched_entity *se) {}
static inline void update_entity_load_avg(struct sched_entity *se,
int update_cfs_rq) {}
static inline void update_rq_runnable_avg(struct rq *rq, int runnable) {}
static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
struct sched_entity *se) {}
struct sched_entity *se,
int wakeup) {}
static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,
struct sched_entity *se) {}
struct sched_entity *se,
int sleep) {}
static inline void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq) {}
#endif
static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
@ -1266,7 +1347,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
*/
update_curr(cfs_rq);
update_cfs_load(cfs_rq, 0);
enqueue_entity_load_avg(cfs_rq, se);
enqueue_entity_load_avg(cfs_rq, se, flags & ENQUEUE_WAKEUP);
account_entity_enqueue(cfs_rq, se);
update_cfs_shares(cfs_rq);
@ -1341,7 +1422,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
* Update run-time statistics of the 'current'.
*/
update_curr(cfs_rq);
dequeue_entity_load_avg(cfs_rq, se);
dequeue_entity_load_avg(cfs_rq, se, flags & DEQUEUE_SLEEP);
update_stats_dequeue(cfs_rq, se);
if (flags & DEQUEUE_SLEEP) {
@ -1512,7 +1593,7 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *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);
update_entity_load_avg(prev, 1);
}
cfs_rq->curr = NULL;
}
@ -1528,7 +1609,8 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
/*
* Ensure that runnable average is periodically updated.
*/
update_entity_load_avg(curr);
update_entity_load_avg(curr, 1);
update_cfs_rq_blocked_load(cfs_rq);
/*
* Update share accounting for long-running entities.
@ -2387,6 +2469,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
update_cfs_load(cfs_rq, 0);
update_cfs_shares(cfs_rq);
update_entity_load_avg(se, 1);
}
if (!se) {
@ -2448,6 +2531,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
update_cfs_load(cfs_rq, 0);
update_cfs_shares(cfs_rq);
update_entity_load_avg(se, 1);
}
if (!se) {
@ -3498,6 +3582,7 @@ static int update_shares_cpu(struct task_group *tg, int cpu)
update_rq_clock(rq);
update_cfs_load(cfs_rq, 1);
update_cfs_rq_blocked_load(cfs_rq);
/*
* We need to update shares after updating tg->load_weight in
@ -5232,6 +5317,20 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
place_entity(cfs_rq, se, 0);
se->vruntime -= cfs_rq->min_vruntime;
}
#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)
/*
* Remove our load from contribution when we leave sched_fair
* and ensure we don't carry in an old decay_count if we
* switch back.
*/
if (p->se.avg.decay_count) {
struct cfs_rq *cfs_rq = cfs_rq_of(&p->se);
__synchronize_entity_decay(&p->se);
subtract_blocked_load_contrib(cfs_rq,
p->se.avg.load_avg_contrib);
}
#endif
}
/*
@ -5278,6 +5377,9 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
#ifndef CONFIG_64BIT
cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)
atomic64_set(&cfs_rq->decay_counter, 1);
#endif
}
#ifdef CONFIG_FAIR_GROUP_SCHED

4
kernel/sched/sched.h
View File

@ -229,7 +229,9 @@ struct cfs_rq {
* This allows for the description of both thread and group usage (in
* the FAIR_GROUP_SCHED case).
*/
u64 runnable_load_avg;
u64 runnable_load_avg, blocked_load_avg;
atomic64_t decay_counter;
u64 last_decay;
#endif
#ifdef CONFIG_FAIR_GROUP_SCHED
struct rq *rq; /* cpu runqueue to which this cfs_rq is attached */