[patch 02/16] sched: hierarchical task accounting for SCHED_OTHER

Paul Turner
2011-06-21T07:27:01Z

[-- Attachment #1: sched-bwc-account_nr_running.patch --]
[-- Type: text/plain, Size: 4530 bytes --]

Introduce hierarchical task accounting for the group scheduling case in CFS, as
well as promoting the responsibility for maintaining rq->nr_running to the
scheduling classes.

The primary motivation for this is that with scheduling classes supporting
bandwidth throttling it is possible for entities participating in throttled
sub-trees to not have root visible changes in rq->nr_running across activate
and de-activate operations. This in turn leads to incorrect idle and
weight-per-task load balance decisions.

This also allows us to make a small fixlet to the fastpath in pick_next_task()
under group scheduling.

Note: this issue also exists with the existing sched_rt throttling mechanism.
This patch does not address that.

Signed-off-by: Paul Turner <pjt@google.com>
Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>

---
kernel/sched.c | 6 ++----
kernel/sched_fair.c | 10 ++++++++--
kernel/sched_rt.c | 5 ++++-
kernel/sched_stoptask.c | 2 ++
4 files changed, 16 insertions(+), 7 deletions(-)

Index: tip/kernel/sched.c
===================================================================
--- tip.orig/kernel/sched.c
+++ tip/kernel/sched.c
@@ -308,7 +308,7 @@ struct task_group root_task_group;
/* CFS-related fields in a runqueue */
struct cfs_rq {
struct load_weight load;
- unsigned long nr_running;
+ unsigned long nr_running, h_nr_running;

u64 exec_clock;
u64 min_vruntime;
@@ -1830,7 +1830,6 @@ static void activate_task(struct rq *rq,
rq->nr_uninterruptible--;

enqueue_task(rq, p, flags);
- inc_nr_running(rq);
}

/*
@@ -1842,7 +1841,6 @@ static void deactivate_task(struct rq *r
rq->nr_uninterruptible++;

dequeue_task(rq, p, flags);
- dec_nr_running(rq);
}

#ifdef CONFIG_IRQ_TIME_ACCOUNTING
@@ -4194,7 +4192,7 @@ pick_next_task(struct rq *rq)
* Optimization: we know that if all tasks are in
* the fair class we can call that function directly:
*/
- if (likely(rq->nr_running == rq->cfs.nr_running)) {
+ if (likely(rq->nr_running == rq->cfs.h_nr_running)) {
p = fair_sched_class.pick_next_task(rq);
if (likely(p))
return p;
Index: tip/kernel/sched_fair.c
===================================================================
--- tip.orig/kernel/sched_fair.c
+++ tip/kernel/sched_fair.c
@@ -1332,16 +1332,19 @@ enqueue_task_fair(struct rq *rq, struct
break;
cfs_rq = cfs_rq_of(se);
enqueue_entity(cfs_rq, se, flags);
+ cfs_rq->h_nr_running++;
flags = ENQUEUE_WAKEUP;
}

for_each_sched_entity(se) {
- struct cfs_rq *cfs_rq = cfs_rq_of(se);
+ cfs_rq = cfs_rq_of(se);
+ cfs_rq->h_nr_running++;

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

+ inc_nr_running(rq);
hrtick_update(rq);
}

@@ -1361,6 +1364,7 @@ static void dequeue_task_fair(struct rq
for_each_sched_entity(se) {
cfs_rq = cfs_rq_of(se);
dequeue_entity(cfs_rq, se, flags);
+ cfs_rq->h_nr_running--;

/* Don't dequeue parent if it has other entities besides us */
if (cfs_rq->load.weight) {
@@ -1379,12 +1383,14 @@ static void dequeue_task_fair(struct rq
}

for_each_sched_entity(se) {
- struct cfs_rq *cfs_rq = cfs_rq_of(se);
+ cfs_rq = cfs_rq_of(se);
+ cfs_rq->h_nr_running--;

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

+ dec_nr_running(rq);
hrtick_update(rq);
}

Index: tip/kernel/sched_rt.c
===================================================================
--- tip.orig/kernel/sched_rt.c
+++ tip/kernel/sched_rt.c
@@ -949,6 +949,8 @@ enqueue_task_rt(struct rq *rq, struct ta

if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1)
enqueue_pushable_task(rq, p);
+
+ inc_nr_running(rq);
}

static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
@@ -959,6 +961,8 @@ static void dequeue_task_rt(struct rq *r
dequeue_rt_entity(rt_se);

dequeue_pushable_task(rq, p);
+
+ dec_nr_running(rq);
}

/*
@@ -1851,4 +1855,3 @@ static void print_rt_stats(struct seq_fi
rcu_read_unlock();
}
#endif /* CONFIG_SCHED_DEBUG */
-
Index: tip/kernel/sched_stoptask.c
===================================================================
--- tip.orig/kernel/sched_stoptask.c
+++ tip/kernel/sched_stoptask.c
@@ -34,11 +34,13 @@ static struct task_struct *pick_next_tas
static void
enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
{
+ inc_nr_running(rq);
}

static void
dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
{
+ dec_nr_running(rq);
}

static void yield_task_stop(struct rq *rq)