Now that the group hierarchy can have an arbitrary depth the O(n^2) nature of RT task dequeues will really hurt. Optimize this by providing space to store the tree path, so we can walk it the other way. Signed-off-by: Peter Zijlstra --- include/linux/sched.h | 1 + kernel/sched_rt.c | 28 ++++++++++++---------------- 2 files changed, 13 insertions(+), 16 deletions(-) Index: linux-2.6-2/kernel/sched_rt.c =================================================================== --- linux-2.6-2.orig/kernel/sched_rt.c +++ linux-2.6-2/kernel/sched_rt.c @@ -479,26 +479,22 @@ static void dequeue_rt_entity(struct sch /* * Because the prio of an upper entry depends on the lower * entries, we must remove entries top - down. - * - * XXX: O(1/2 h^2) because we can only walk up, not down the chain. */ static void dequeue_rt_stack(struct task_struct *p) { - struct sched_rt_entity *rt_se, *top_se; + struct sched_rt_entity *rt_se, *back = NULL; - /* - * dequeue all, top - down. - */ - do { - rt_se = &p->rt; - top_se = NULL; - for_each_sched_rt_entity(rt_se) { - if (on_rt_rq(rt_se)) - top_se = rt_se; - } - if (top_se) - dequeue_rt_entity(top_se); - } while (top_se); + rt_se = &p->rt; + for_each_sched_rt_entity(rt_se) { + if (!on_rt_rq(rt_se)) + break; + + rt_se->back = back; + back = rt_se; + } + + for (rt_se = back; rt_se; rt_se = rt_se->back) + dequeue_rt_entity(rt_se); } /* Index: linux-2.6-2/include/linux/sched.h =================================================================== --- linux-2.6-2.orig/include/linux/sched.h +++ linux-2.6-2/include/linux/sched.h @@ -978,6 +978,7 @@ struct sched_rt_entity { unsigned long timeout; int nr_cpus_allowed; + struct sched_rt_entity *back; #ifdef CONFIG_RT_GROUP_SCHED struct sched_rt_entity *parent; /* rq on which this entity is (to be) queued: */ -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/