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Subject[tip:sched/urgent] sched/rt: Improve pick_next_highest_task_rt()
Commit-ID:  1b028abc779b67b699daff55e27d2432f8d92666
Author: Michael J Wang <>
AuthorDate: Mon, 19 Mar 2012 22:26:19 +0000
Committer: Ingo Molnar <>
CommitDate: Tue, 27 Mar 2012 14:52:12 +0200

sched/rt: Improve pick_next_highest_task_rt()

Avoid extra work by continuing on to the next rt_rq if the highest
prio task in current rt_rq is the same priority as our candidate

More detailed explanation: if next is not NULL, then we have found a
candidate task, and its priority is next->prio. Now we are looking
for an even higher priority task in the other rt_rq's. idx is the
highest priority in the current candidate rt_rq. In the current 3.3
code, if idx is equal to next->prio, we would start scanning the tasks
in that rt_rq and replace the current candidate task with a task from
that rt_rq. But the new task would only have a priority that is equal
to our previous candidate task, so we have not advanced our goal of
finding a higher prio task. So we should avoid the extra work by
continuing on to the next rt_rq if idx is equal to next->prio.

Signed-off-by: Michael J Wang <>
Acked-by: Steven Rostedt <>
Reviewed-by: Yong Zhang <>
Signed-off-by: Peter Zijlstra <>
Signed-off-by: Ingo Molnar <>
kernel/sched/rt.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index b60dad7..44af55e 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1428,7 +1428,7 @@ static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu)
if (idx >= MAX_RT_PRIO)
- if (next && next->prio < idx)
+ if (next && next->prio <= idx)
list_for_each_entry(rt_se, array->queue + idx, run_list) {
struct task_struct *p;

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