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Subject[RFC PATCH 11/14] sched: refactor update_shares_cpu() -> update_blocked_avgs()
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Now that running entities maintain their own load-averages the work we must do
in update_shares() is largely restricted to the periodic decay of blocked
entities. This allows us to be a little less pessimistic regarding our
occupancy on rq->lock and the associated rq->clock updates required.

We also no longer use the instantaneous load to calculate group-entity
load-weight. This was previously required as a compromise since migrated load
would remain in the parenting average while it decayed, however it leads to
over-allocation of shares.

Signed-off-by: Paul Turner <pjt@google.com>
---
kernel/sched/fair.c | 57 ++++++++++++++++++++++++++++-----------------------
1 files changed, 31 insertions(+), 26 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 46b3f98..5b6ee7a4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -823,7 +823,7 @@ static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq)
*/
tg_weight = atomic64_read(&tg->load_avg);
tg_weight -= cfs_rq->tg_load_contrib;
- tg_weight += cfs_rq->load.weight;
+ tg_weight += cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg;

return tg_weight;
}
@@ -833,7 +833,7 @@ static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
long tg_weight, load, shares;

tg_weight = calc_tg_weight(tg, cfs_rq);
- load = cfs_rq->load.weight;
+ load = cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg;

shares = (tg->shares * load);
if (tg_weight)
@@ -3559,21 +3559,16 @@ out:
/*
* update tg->load_weight by folding this cpu's load_avg
*/
-static int update_shares_cpu(struct task_group *tg, int cpu)
+static void __update_blocked_averages_cpu(struct task_group *tg, int cpu)
{
- struct sched_entity *se;
- struct cfs_rq *cfs_rq;
- unsigned long flags;
+ struct sched_entity *se = tg->se[cpu];
+ struct cfs_rq *cfs_rq = tg->cfs_rq[cpu];
struct rq *rq;

+ /* throttled entities do not contribute to load */
+ if (throttled_hierarchy(cfs_rq))
+ return;

- rq = cpu_rq(cpu);
- se = tg->se[cpu];
- cfs_rq = tg->cfs_rq[cpu];
-
- raw_spin_lock_irqsave(&rq->lock, flags);
-
- update_rq_clock(rq);
update_cfs_rq_blocked_load(cfs_rq, 1);

if (se) {
@@ -3586,29 +3581,39 @@ static int update_shares_cpu(struct task_group *tg, int cpu)
else
list_del_leaf_cfs_rq(cfs_rq);
}
-
- raw_spin_unlock_irqrestore(&rq->lock, flags);
-
- return 0;
}

-static void update_shares(int cpu)
+static void update_blocked_averages(int cpu)
{
- struct cfs_rq *cfs_rq;
struct rq *rq = cpu_rq(cpu);
+ struct cfs_rq *cfs_rq;
+
+ unsigned long flags;
+ int num_updates = 0;

rcu_read_lock();
+ raw_spin_lock_irqsave(&rq->lock, flags);
+ update_rq_clock(rq);
/*
* Iterates the task_group tree in a bottom up fashion, see
* list_add_leaf_cfs_rq() for details.
*/
for_each_leaf_cfs_rq(rq, cfs_rq) {
- /* throttled entities do not contribute to load */
- if (throttled_hierarchy(cfs_rq))
- continue;
+ __update_blocked_averages_cpu(cfs_rq->tg, rq->cpu);

- update_shares_cpu(cfs_rq->tg, cpu);
+ /*
+ * Periodically release the lock so that a cfs_rq with many
+ * children cannot hold it for an arbitrary period of time.
+ */
+ if (num_updates++ % 20 == 0) {
+ raw_spin_unlock_irqrestore(&rq->lock, flags);
+ cpu_relax();
+ raw_spin_lock_irqsave(&rq->lock, flags);
+ update_rq_clock(rq);
+ }
}
+
+ raw_spin_unlock_irqrestore(&rq->lock, flags);
rcu_read_unlock();
}

@@ -3689,7 +3694,7 @@ load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
return max_load_move - rem_load_move;
}
#else
-static inline void update_shares(int cpu)
+static inline void update_blocked_averages(int cpu)
{
}

@@ -4917,7 +4922,7 @@ void idle_balance(int this_cpu, struct rq *this_rq)
*/
raw_spin_unlock(&this_rq->lock);

- update_shares(this_cpu);
+ update_blocked_averages(this_cpu);
rcu_read_lock();
for_each_domain(this_cpu, sd) {
unsigned long interval;
@@ -5258,7 +5263,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
int update_next_balance = 0;
int need_serialize;

- update_shares(cpu);
+ update_blocked_averages(cpu);

rcu_read_lock();
for_each_domain(cpu, sd) {



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