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Subject[tg_shares_up rewrite v3 05/11] sched: fix update_cfs_load synchronization
Using cfs_rq->nr_running is not sufficient to synchronize update_cfs_load with
the put path since nr_running accounting occurs at deactivation.

It's also not safe to make the removal decision based on load_avg as this fails
with both high periods and low shares. Resolve this by clipping history after 4
periods without activity.

Note: the above will always occur from update_shares() since in the
last-task-sleep-case that task will still be cfs_rq->curr when update_cfs_load is
called.

Signed-off-by: Paul Turner <pjt@google.com>

---
kernel/sched.c | 2 +-
kernel/sched_fair.c | 33 +++++++++++++++++++++------------
2 files changed, 22 insertions(+), 13 deletions(-)
Index: kernel/sched_fair.c
===================================================================
--- kernel/sched_fair.c.orig
+++ kernel/sched_fair.c
@@ -674,10 +674,11 @@ account_entity_dequeue(struct cfs_rq *cf
}

#if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED
-static void update_cfs_load(struct cfs_rq *cfs_rq, int lb)
+static void update_cfs_load(struct cfs_rq *cfs_rq)
{
u64 period = sched_avg_period();
u64 now, delta;
+ unsigned long load = cfs_rq->load.weight;

if (!cfs_rq)
return;
@@ -685,9 +686,19 @@ static void update_cfs_load(struct cfs_r
now = rq_of(cfs_rq)->clock;
delta = now - cfs_rq->load_stamp;

+ /* truncate load history at 4 idle periods */
+ if (cfs_rq->load_stamp > cfs_rq->load_last &&
+ now - cfs_rq->load_last > 4 * period) {
+ cfs_rq->load_period = 0;
+ cfs_rq->load_avg = 0;
+ }
+
cfs_rq->load_stamp = now;
cfs_rq->load_period += delta;
- cfs_rq->load_avg += delta * cfs_rq->load.weight;
+ if (load) {
+ cfs_rq->load_last = now;
+ cfs_rq->load_avg += delta * load;
+ }

while (cfs_rq->load_period > period) {
/*
@@ -700,10 +711,8 @@ static void update_cfs_load(struct cfs_r
cfs_rq->load_avg /= 2;
}

- if (lb && !cfs_rq->nr_running) {
- if (cfs_rq->load_avg < (period / 8))
- list_del_leaf_cfs_rq(cfs_rq);
- }
+ if (!cfs_rq->curr && !cfs_rq->nr_running && !cfs_rq->load_avg)
+ list_del_leaf_cfs_rq(cfs_rq);
}

static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
@@ -750,7 +759,7 @@ static void update_cfs_shares(struct cfs
reweight_entity(cfs_rq_of(se), se, shares);
}
#else /* CONFIG_FAIR_GROUP_SCHED */
-static inline void update_cfs_load(struct cfs_rq *cfs_rq, int lb)
+static inline void update_cfs_load(struct cfs_rq *cfs_rq)
{
}

@@ -880,7 +889,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
* Update run-time statistics of the 'current'.
*/
update_curr(cfs_rq);
- update_cfs_load(cfs_rq, 0);
+ update_cfs_load(cfs_rq);
update_cfs_shares(cfs_rq, se->load.weight);
account_entity_enqueue(cfs_rq, se);

@@ -941,7 +950,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
if (se != cfs_rq->curr)
__dequeue_entity(cfs_rq, se);
se->on_rq = 0;
- update_cfs_load(cfs_rq, 0);
+ update_cfs_load(cfs_rq);
account_entity_dequeue(cfs_rq, se);
update_min_vruntime(cfs_rq);
update_cfs_shares(cfs_rq, 0);
@@ -1176,7 +1185,7 @@ enqueue_task_fair(struct rq *rq, struct
for_each_sched_entity(se) {
struct cfs_rq *cfs_rq = cfs_rq_of(se);

- update_cfs_load(cfs_rq, 0);
+ update_cfs_load(cfs_rq);
update_cfs_shares(cfs_rq, 0);
}

@@ -1206,7 +1215,7 @@ static void dequeue_task_fair(struct rq
for_each_sched_entity(se) {
struct cfs_rq *cfs_rq = cfs_rq_of(se);

- update_cfs_load(cfs_rq, 0);
+ update_cfs_load(cfs_rq);
update_cfs_shares(cfs_rq, 0);
}

@@ -2019,7 +2028,7 @@ static int tg_shares_up(struct task_grou
raw_spin_lock_irqsave(&rq->lock, flags);

update_rq_clock(rq);
- update_cfs_load(cfs_rq, 1);
+ update_cfs_load(cfs_rq);

load_avg = div64_u64(cfs_rq->load_avg, cfs_rq->load_period+1);
load_avg -= cfs_rq->load_contribution;
Index: kernel/sched.c
===================================================================
--- kernel/sched.c.orig
+++ kernel/sched.c
@@ -357,7 +357,7 @@ struct cfs_rq {

u64 load_avg;
u64 load_period;
- u64 load_stamp;
+ u64 load_stamp, load_last;

unsigned long load_contribution;
#endif
--



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