[PATCH 3.2 19/24] sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target
From: Ben Hutchings
Date: Tue Mar 03 2015 - 18:23:24 EST
3.2.68-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
commit 80e3d87b2c5582db0ab5e39610ce3707d97ba409 upstream.
This patch adds checks that prevens futile attempts to move rt tasks
to a CPU with active tasks of equal or higher priority.
This reduces run queue lock contention and improves the performance of
a well known OLTP benchmark by 0.7%.
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Shawn Bohrer <sbohrer@xxxxxxxxxxxxxxx>
Cc: Suruchi Kadu <suruchi.a.kadu@xxxxxxxxx>
Cc: Doug Nelson<doug.nelson@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1421430374.2399.27.camel@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
kernel/sched_rt.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1067,7 +1067,12 @@ select_task_rq_rt(struct task_struct *p,
(p->rt.nr_cpus_allowed > 1)) {
int target = find_lowest_rq(p);
- if (target != -1)
+ /*
+ * Don't bother moving it if the destination CPU is
+ * not running a lower priority task.
+ */
+ if (target != -1 &&
+ p->prio < cpu_rq(target)->rt.highest_prio.curr)
cpu = target;
}
rcu_read_unlock();
@@ -1346,6 +1351,16 @@ static struct rq *find_lock_lowest_rq(st
lowest_rq = cpu_rq(cpu);
+ if (lowest_rq->rt.highest_prio.curr <= task->prio) {
+ /*
+ * Target rq has tasks of equal or higher priority,
+ * retrying does not release any lock and is unlikely
+ * to yield a different result.
+ */
+ lowest_rq = NULL;
+ break;
+ }
+
/* if the prio of this runqueue changed, try again */
if (double_lock_balance(rq, lowest_rq)) {
/*
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/