path: root/kernel
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authorKen Chen <kenchen@google.com>2011-04-08 12:20:16 -0700
committerIngo Molnar <mingo@elte.hu>2011-04-11 11:08:54 +0200
commitb30aef17f71cf9e24b10c11cbb5e5f0ebe8a85ab (patch)
tree0e5e0e0d1d93edf934f58b116ee0c4e81db01e72 /kernel
parentb0432d8f162c7d5d9537b4cb749d44076b76a783 (diff)
sched: Fix erroneous all_pinned logic
The scheduler load balancer has specific code to deal with cases of unbalanced system due to lots of unmovable tasks (for example because of hard CPU affinity). In those situation, it excludes the busiest CPU that has pinned tasks for load balance consideration such that it can perform second 2nd load balance pass on the rest of the system. This all works as designed if there is only one cgroup in the system. However, when we have multiple cgroups, this logic has false positives and triggers multiple load balance passes despite there are actually no pinned tasks at all. The reason it has false positives is that the all pinned logic is deep in the lowest function of can_migrate_task() and is too low level: load_balance_fair() iterates each task group and calls balance_tasks() to migrate target load. Along the way, balance_tasks() will also set a all_pinned variable. Given that task-groups are iterated, this all_pinned variable is essentially the status of last group in the scanning process. Task group can have number of reasons that no load being migrated, none due to cpu affinity. However, this status bit is being propagated back up to the higher level load_balance(), which incorrectly think that no tasks were moved. It kick off the all pinned logic and start multiple passes attempt to move load onto puller CPU. To fix this, move the all_pinned aggregation up at the iterator level. This ensures that the status is aggregated over all task-groups, not just last one in the list. Signed-off-by: Ken Chen <kenchen@google.com> Cc: stable@kernel.org Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/BANLkTi=ernzNawaR5tJZEsV_QVnfxqXmsQ@mail.gmail.com Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
1 files changed, 4 insertions, 7 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 60f9d407c5ec..6fa833ab2cb8 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2104,21 +2104,20 @@ balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
enum cpu_idle_type idle, int *all_pinned,
int *this_best_prio, struct cfs_rq *busiest_cfs_rq)
- int loops = 0, pulled = 0, pinned = 0;
+ int loops = 0, pulled = 0;
long rem_load_move = max_load_move;
struct task_struct *p, *n;
if (max_load_move == 0)
goto out;
- pinned = 1;
list_for_each_entry_safe(p, n, &busiest_cfs_rq->tasks, se.group_node) {
if (loops++ > sysctl_sched_nr_migrate)
if ((p->se.load.weight >> 1) > rem_load_move ||
- !can_migrate_task(p, busiest, this_cpu, sd, idle, &pinned))
+ !can_migrate_task(p, busiest, this_cpu, sd, idle,
+ all_pinned))
pull_task(busiest, p, this_rq, this_cpu);
@@ -2153,9 +2152,6 @@ out:
schedstat_add(sd, lb_gained[idle], pulled);
- if (all_pinned)
- *all_pinned = pinned;
return max_load_move - rem_load_move;
@@ -3341,6 +3337,7 @@ redo:
* still unbalanced. ld_moved simply stays zero, so it is
* correctly treated as an imbalance.
+ all_pinned = 1;
double_rq_lock(this_rq, busiest);
ld_moved = move_tasks(this_rq, this_cpu, busiest,

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