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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2011-09-22 15:30:18 +0200
committerIngo Molnar <mingo@elte.hu>2011-12-21 10:34:47 +0100
commita195f004e9496b4d99f471bb96e0a0c1af080909 (patch)
tree605f04617dc42458025cb4341e9e6407bed8b140 /kernel/sched
parent5b54b56be5b540a9cb12682c4d0df5454c098a38 (diff)
sched: Fix load-balance lock-breaking
The current lock break relies on contention on the rq locks, something which might never come because we've got IRQs disabled. Or will be very likely because on anything with more than 2 cpus a synchronized load-balance pass will very likely cause contention on the rq locks. Also the sched_nr_migrate thing fails when it gets trapped the loops of either the cgroup muck in load_balance_fair() or the move_tasks() load condition. Instead, use the new lb_flags field to propagate break/abort conditions for all these loops and create a new loop outside the irq disabled on the break being required. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/n/tip-tsceb6w61q0gakmsccix6xxi@git.kernel.org Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/fair.c32
1 files changed, 25 insertions, 7 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index be47ce6da2a5..cea2fa853274 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3132,6 +3132,8 @@ task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
}
#define LBF_ALL_PINNED 0x01
+#define LBF_NEED_BREAK 0x02
+#define LBF_ABORT 0x04
/*
* can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
@@ -3237,8 +3239,10 @@ balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
goto out;
list_for_each_entry_safe(p, n, &busiest_cfs_rq->tasks, se.group_node) {
- if (loops++ > sysctl_sched_nr_migrate)
+ if (loops++ > sysctl_sched_nr_migrate) {
+ *lb_flags |= LBF_NEED_BREAK;
break;
+ }
if ((p->se.load.weight >> 1) > rem_load_move ||
!can_migrate_task(p, busiest, this_cpu, sd, idle,
@@ -3255,8 +3259,10 @@ balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
* kernels will stop after the first task is pulled to minimize
* the critical section.
*/
- if (idle == CPU_NEWLY_IDLE)
+ if (idle == CPU_NEWLY_IDLE) {
+ *lb_flags |= LBF_ABORT;
break;
+ }
#endif
/*
@@ -3374,6 +3380,9 @@ load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
unsigned long busiest_weight = busiest_cfs_rq->load.weight;
u64 rem_load, moved_load;
+ if (*lb_flags & (LBF_NEED_BREAK|LBF_ABORT))
+ break;
+
/*
* empty group or part of a throttled hierarchy
*/
@@ -3440,18 +3449,19 @@ static int move_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
total_load_moved += load_moved;
+ if (*lb_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 (idle == CPU_NEWLY_IDLE && this_rq->nr_running)
- break;
-
- if (raw_spin_is_contended(&this_rq->lock) ||
- raw_spin_is_contended(&busiest->lock))
+ if (idle == CPU_NEWLY_IDLE && this_rq->nr_running) {
+ *lb_flags |= LBF_ABORT;
break;
+ }
#endif
} while (load_moved && max_load_move > total_load_moved);
@@ -4496,6 +4506,14 @@ redo:
if (ld_moved && this_cpu != smp_processor_id())
resched_cpu(this_cpu);
+ if (lb_flags & LBF_ABORT)
+ goto out_balanced;
+
+ if (lb_flags & LBF_NEED_BREAK) {
+ lb_flags &= ~LBF_NEED_BREAK;
+ goto redo;
+ }
+
/* All tasks on this runqueue were pinned by CPU affinity */
if (unlikely(lb_flags & LBF_ALL_PINNED)) {
cpumask_clear_cpu(cpu_of(busiest), cpus);