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Subject[RFC PATCH 08/14] sched: normalize tg load contributions against runnable time
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Entities of equal weight should receive equitable distribution of cpu time.
This is challenging in the case of a task_group's shares as execution may be
occurring on multiple cpus simultaneously.

To handle this we divide up the shares into weights proportionate with the load
on each cfs_rq. This does not however, account for the fact that the sum of
the parts may be less than one cpu and so we need to normalize:
load(tg) = min(runnable_avg(tg), 1) * tg->shares
Where runnable_avg is the aggregate time in which the task_group had runnable
children.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Ben Segall <bsegall@google.com>.
---
kernel/sched/debug.c | 4 ++++
kernel/sched/fair.c | 34 ++++++++++++++++++++++++++++++++++
kernel/sched/sched.h | 2 ++
3 files changed, 40 insertions(+), 0 deletions(-)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index f6227c0..8d87796 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -232,6 +232,10 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
atomic64_read(&cfs_rq->tg->load_avg));
SEQ_printf(m, " .%-30s: %lld\n", "tg_load_contrib",
cfs_rq->tg_load_contrib);
+ SEQ_printf(m, " .%-30s: %d\n", "tg_runnable_contrib",
+ cfs_rq->tg_runnable_contrib);
+ SEQ_printf(m, " .%-30s: %d\n", "tg->runnable_avg",
+ atomic_read(&cfs_rq->tg->runnable_avg));
#endif

print_cfs_group_stats(m, cpu, cfs_rq->tg);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6d8af5e..803c622 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1103,13 +1103,45 @@ static inline void __update_task_entity_contrib(struct sched_entity *se)
se->avg.runnable_avg_period + 1);
}

+/*
+ * Aggregate cfs_rq runnable averages into an equivalent task_group
+ * representation for computing load contributions.
+ */
+static inline void __update_tg_runnable_avg(struct sched_avg *sa,
+ struct cfs_rq *cfs_rq)
+{
+ struct task_group *tg = cfs_rq->tg;
+ long contrib;
+
+ contrib = (sa->runnable_avg_sum << 12) / (sa->runnable_avg_period + 1);
+ contrib -= cfs_rq->tg_runnable_contrib;
+
+ if (abs(contrib) > cfs_rq->tg_runnable_contrib/64) {
+ atomic_add(contrib, &tg->runnable_avg);
+ cfs_rq->tg_runnable_contrib += contrib;
+ }
+}
+
static inline void __update_group_entity_contrib(struct sched_entity *se)
{
struct cfs_rq *cfs_rq = group_cfs_rq(se);
struct task_group *tg = cfs_rq->tg;
+ int runnable_avg;

se->avg.load_avg_contrib = (cfs_rq->tg_load_contrib * tg->shares);
se->avg.load_avg_contrib /= atomic64_read(&tg->load_avg) + 1;
+
+ /*
+ * Unlike a task-entity, a group entity may be using >=1 cpu globally.
+ * However, in the case that it's using <1 cpu we need to form a
+ * correction term so that we contribute the same load as a task of
+ * equal weight. (Global runnable time is taken as a fraction over 2^12.)
+ */
+ runnable_avg = atomic_read(&tg->runnable_avg);
+ if (runnable_avg < (1<<12)) {
+ se->avg.load_avg_contrib *= runnable_avg;
+ se->avg.load_avg_contrib /= (1<<12);
+ }
}

/* Compute the current contribution to load_avg by se, return any delta */
@@ -1122,6 +1154,7 @@ static long __update_entity_load_avg_contrib(struct sched_entity *se)
} else {
if (!se->on_rq)
__synchronize_entity_decay(se);
+ __update_tg_runnable_avg(&se->avg, group_cfs_rq(se));
__update_group_entity_contrib(se);
}

@@ -1205,6 +1238,7 @@ static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq, int force_update)
static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
{
__update_entity_runnable_avg(rq->clock_task, &rq->avg, runnable);
+ __update_tg_runnable_avg(&rq->avg, &rq->cfs);
}

/* Add the load generated by se into cfs_rq's child load-average */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 17f99e7..57cc227 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -117,6 +117,7 @@ struct task_group {

atomic_t load_weight;
atomic64_t load_avg;
+ atomic_t runnable_avg;
#endif

#ifdef CONFIG_RT_GROUP_SCHED
@@ -272,6 +273,7 @@ struct cfs_rq {

unsigned long load_contribution;

+ u32 tg_runnable_contrib;
u64 runnable_load_avg, blocked_load_avg;
u64 tg_load_contrib;
atomic64_t decay_counter, removed_load;



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