On 02/18/2013 01:07 PM, Alex Shi wrote:
> New task has no runnable sum at its first runnable time, so its
> runnable load is zero. That makes burst forking balancing just select
> few idle cpus to assign tasks if we engage runnable load in balancing.
>
> Set initial load avg of new forked task as its load weight to resolve
> this issue.
>
patch answering PJT's update here. that merged the 1st and 2nd patches
into one. other patches in serial don't need to change.
=========
>From 89b56f2e5a323a0cb91c98be15c94d34e8904098 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex....@intel.com>
Date: Mon, 3 Dec 2012 17:30:39 +0800
Subject: [PATCH 01/14] sched: set initial value of runnable avg for new
forked task
We need initialize the se.avg.{decay_count, load_avg_contrib} for a
new forked task.
Otherwise random values of above variables cause mess when do new task
enqueue:
enqueue_task_fair
enqueue_entity
enqueue_entity_load_avg
and make forking balancing imbalance since incorrect load_avg_contrib.
set avg.decay_count = 0, and avg.load_avg_contrib = se->load.weight to
resolve such issues.
Signed-off-by: Alex Shi <alex....@intel.com>
---
kernel/sched/core.c | 3 +++
kernel/sched/fair.c | 4 ++++
2 files changed, 7 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 26058d0..1452e14 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1559,6 +1559,7 @@ static void __sched_fork(struct task_struct *p)
#if defined(CONFIG_SMP) && defined(CONFIG_FAIR_GROUP_SCHED)
p->se.avg.runnable_avg_period = 0;
p->se.avg.runnable_avg_sum = 0;
+ p->se.avg.decay_count = 0;
#endif
#ifdef CONFIG_SCHEDSTATS
memset(&p->se.statistics, 0, sizeof(p->se.statistics));
@@ -1646,6 +1647,8 @@ void sched_fork(struct task_struct *p)
p->sched_reset_on_fork = 0;
}
+ p->se.avg.load_avg_contrib = p->se.load.weight;
+
if (!rt_prio(p->prio))
p->sched_class = &fair_sched_class;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 81fa536..cae5134 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1509,6 +1509,10 @@ static inline void enqueue_entity_load_avg(struct cfs_rq
*cfs_rq,
* We track migrations using entity decay_count <= 0, on a wake-up
* migration we use a negative decay count to track the remote decays
* accumulated while sleeping.
+ *
+ * When enqueue a new forked task, the se->avg.decay_count == 0, so
+ * we bypass update_entity_load_avg(), use avg.load_avg_contrib initial
+ * value: se->load.weight.
*/
if (unlikely(se->avg.decay_count <= 0)) {
se->avg.last_runnable_update = rq_of(cfs_rq)->clock_task;
--
1.7.12
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