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Date: Mon, 12 Mar 2012 21:44:19 -0700
From: tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
a.p.zijlstra@...llo.nl, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/core] sched: Fix load-balance wreckage
Commit-ID: 5d6523ebd2f67de9d23285aad7f3910e7b0aee83
Gitweb: http://git.kernel.org/tip/5d6523ebd2f67de9d23285aad7f3910e7b0aee83
Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Sat, 10 Mar 2012 00:07:36 +0100
Committer: Ingo Molnar <mingo@...e.hu>
CommitDate: Mon, 12 Mar 2012 20:43:15 +0100
sched: Fix load-balance wreckage
Commit 367456c ("sched: Ditch per cgroup task lists for
load-balancing") completely wrecked load-balancing due to
a few silly mistakes.
Correct those and remove more pointless code.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/n/tip-zk04ihygwxn7qqrlpaf73b0r@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
kernel/sched/fair.c | 110 ++++++++++++++++++---------------------------------
1 files changed, 39 insertions(+), 71 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a0424fc..def17aa 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -784,7 +784,7 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
update_load_add(&rq_of(cfs_rq)->load, se->load.weight);
#ifdef CONFIG_SMP
if (entity_is_task(se))
- list_add(&se->group_node, &rq_of(cfs_rq)->cfs_tasks);
+ list_add_tail(&se->group_node, &rq_of(cfs_rq)->cfs_tasks);
#endif
cfs_rq->nr_running++;
}
@@ -3071,7 +3071,6 @@ static unsigned long __read_mostly max_load_balance_interval = HZ/10;
#define LBF_ALL_PINNED 0x01
#define LBF_NEED_BREAK 0x02
-#define LBF_ABORT 0x04
struct lb_env {
struct sched_domain *sd;
@@ -3083,7 +3082,7 @@ struct lb_env {
struct rq *dst_rq;
enum cpu_idle_type idle;
- unsigned long max_load_move;
+ long load_move;
unsigned int flags;
unsigned int loop;
@@ -3216,39 +3215,47 @@ static int move_one_task(struct lb_env *env)
static unsigned long task_h_load(struct task_struct *p);
-static unsigned long balance_tasks(struct lb_env *env)
+/*
+ * move_tasks tries to move up to load_move weighted load from busiest to
+ * this_rq, as part of a balancing operation within domain "sd".
+ * Returns 1 if successful and 0 otherwise.
+ *
+ * Called with both runqueues locked.
+ */
+static int move_tasks(struct lb_env *env)
{
- long rem_load_move = env->max_load_move;
- struct task_struct *p, *n;
+ struct list_head *tasks = &env->src_rq->cfs_tasks;
+ struct task_struct *p;
unsigned long load;
int pulled = 0;
- if (env->max_load_move == 0)
- goto out;
+ if (env->load_move <= 0)
+ return 0;
+
+ while (!list_empty(tasks)) {
+ p = list_first_entry(tasks, struct task_struct, se.group_node);
- list_for_each_entry_safe(p, n, &env->src_rq->cfs_tasks, se.group_node) {
env->loop++;
/* We've more or less seen every task there is, call it quits */
- if (env->loop > env->loop_max) {
- env->flags |= LBF_ABORT;
+ if (env->loop > env->loop_max)
break;
- }
- /* take a beather every nr_migrate tasks */
+
+ /* take a breather every nr_migrate tasks */
if (env->loop > env->loop_break) {
env->loop_break += sysctl_sched_nr_migrate;
env->flags |= LBF_NEED_BREAK;
break;
}
- if (throttled_lb_pair(task_group(p), env->src_rq->cpu,
- env->dst_cpu))
+ if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
goto next;
load = task_h_load(p);
+
if (load < 16 && !env->sd->nr_balance_failed)
goto next;
- if ((load * 2) > rem_load_move)
+ if ((load / 2) > env->load_move)
goto next;
if (!can_migrate_task(p, env))
@@ -3256,7 +3263,7 @@ static unsigned long balance_tasks(struct lb_env *env)
move_task(p, env);
pulled++;
- rem_load_move -= load;
+ env->load_move -= load;
#ifdef CONFIG_PREEMPT
/*
@@ -3264,24 +3271,22 @@ static unsigned long balance_tasks(struct lb_env *env)
* kernels will stop after the first task is pulled to minimize
* the critical section.
*/
- if (env->idle == CPU_NEWLY_IDLE) {
- env->flags |= LBF_ABORT;
+ if (env->idle == CPU_NEWLY_IDLE)
break;
- }
#endif
/*
* We only want to steal up to the prescribed amount of
* weighted load.
*/
- if (rem_load_move <= 0)
+ if (env->load_move <= 0)
break;
continue;
next:
- list_move_tail(&p->se.group_node, &env->src_rq->cfs_tasks);
+ list_move_tail(&p->se.group_node, tasks);
}
-out:
+
/*
* Right now, this is one of only two places move_task() is called,
* so we can safely collect move_task() stats here rather than
@@ -3289,7 +3294,7 @@ out:
*/
schedstat_add(env->sd, lb_gained[env->idle], pulled);
- return env->max_load_move - rem_load_move;
+ return pulled;
}
#ifdef CONFIG_FAIR_GROUP_SCHED
@@ -3399,43 +3404,6 @@ static unsigned long task_h_load(struct task_struct *p)
}
#endif
-/*
- * move_tasks tries to move up to max_load_move weighted load from busiest to
- * this_rq, as part of a balancing operation within domain "sd".
- * Returns 1 if successful and 0 otherwise.
- *
- * Called with both runqueues locked.
- */
-static int move_tasks(struct lb_env *env)
-{
- unsigned long max_load_move = env->max_load_move;
- unsigned long total_load_moved = 0, load_moved;
-
- update_h_load(cpu_of(env->src_rq));
- do {
- env->max_load_move = max_load_move - total_load_moved;
- load_moved = balance_tasks(env);
- total_load_moved += load_moved;
-
- if (env->flags & (LBF_NEED_BREAK|LBF_ABORT))
- break;
-
-#ifdef CONFIG_PREEMPT
- /*
- * NEWIDLE balancing is a source of latency, so preemptible
- * kernels will stop after the first task is pulled to minimize
- * the critical section.
- */
- if (env->idle == CPU_NEWLY_IDLE && env->dst_rq->nr_running) {
- env->flags |= LBF_ABORT;
- break;
- }
-#endif
- } while (load_moved && max_load_move > total_load_moved);
-
- return total_load_moved > 0;
-}
-
/********** Helpers for find_busiest_group ************************/
/*
* sd_lb_stats - Structure to store the statistics of a sched_domain
@@ -4477,31 +4445,31 @@ redo:
* correctly treated as an imbalance.
*/
env.flags |= LBF_ALL_PINNED;
- env.max_load_move = imbalance;
+ env.load_move = imbalance;
env.src_cpu = busiest->cpu;
env.src_rq = busiest;
env.loop_max = busiest->nr_running;
+more_balance:
local_irq_save(flags);
double_rq_lock(this_rq, busiest);
- ld_moved = move_tasks(&env);
+ if (!env.loop)
+ update_h_load(env.src_cpu);
+ ld_moved += move_tasks(&env);
double_rq_unlock(this_rq, busiest);
local_irq_restore(flags);
+ if (env.flags & LBF_NEED_BREAK) {
+ env.flags &= ~LBF_NEED_BREAK;
+ goto more_balance;
+ }
+
/*
* some other cpu did the load balance for us.
*/
if (ld_moved && this_cpu != smp_processor_id())
resched_cpu(this_cpu);
- if (env.flags & LBF_ABORT)
- goto out_balanced;
-
- if (env.flags & LBF_NEED_BREAK) {
- env.flags &= ~LBF_NEED_BREAK;
- goto redo;
- }
-
/* All tasks on this runqueue were pinned by CPU affinity */
if (unlikely(env.flags & LBF_ALL_PINNED)) {
cpumask_clear_cpu(cpu_of(busiest), cpus);
--
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