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author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2007-11-09 21:39:39 (GMT) |
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committer | Ingo Molnar <mingo@elte.hu> | 2007-11-09 21:39:39 (GMT) |
commit | b82d9fdd848abfbe7263a4ecd9bbb55e575100a6 (patch) | |
tree | 7d4c525cc4bd633c84abcfd8d934c84e5dc9ce7c /kernel/sched.c | |
parent | 3c90e6e99b08f01d5684a3a07cceae6a543e4fa8 (diff) | |
download | linux-fsl-qoriq-b82d9fdd848abfbe7263a4ecd9bbb55e575100a6.tar.xz |
sched: avoid large irq-latencies in smp-balancing
SMP balancing is done with IRQs disabled and can iterate the full rq.
When rqs are large this can cause large irq-latencies. Limit the nr of
iterations on each run.
This fixes a scheduling latency regression reported by the -rt folks.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r-- | kernel/sched.c | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index 2a107e4..e195a42 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -472,6 +472,12 @@ const_debug unsigned int sysctl_sched_features = #define sched_feat(x) (sysctl_sched_features & SCHED_FEAT_##x) /* + * Number of tasks to iterate in a single balance run. + * Limited because this is done with IRQs disabled. + */ +const_debug unsigned int sysctl_sched_nr_migrate = 32; + +/* * For kernel-internal use: high-speed (but slightly incorrect) per-cpu * clock constructed from sched_clock(): */ @@ -2235,7 +2241,7 @@ 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 rq_iterator *iterator) { - int pulled = 0, pinned = 0, skip_for_load; + int loops = 0, pulled = 0, pinned = 0, skip_for_load; struct task_struct *p; long rem_load_move = max_load_move; @@ -2249,10 +2255,10 @@ balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest, */ p = iterator->start(iterator->arg); next: - if (!p) + if (!p || loops++ > sysctl_sched_nr_migrate) goto out; /* - * To help distribute high priority tasks accross CPUs we don't + * To help distribute high priority tasks across CPUs we don't * skip a task if it will be the highest priority task (i.e. smallest * prio value) on its new queue regardless of its load weight */ @@ -2269,8 +2275,7 @@ next: rem_load_move -= p->se.load.weight; /* - * We only want to steal up to the prescribed number of tasks - * and the prescribed amount of weighted load. + * We only want to steal up to the prescribed amount of weighted load. */ if (rem_load_move > 0) { if (p->prio < *this_best_prio) |