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* [PATCH] Repost sched-rt: Reduce rq lock contention by eliminating locking of non-feasible target
@ 2015-01-06 19:01 Tim Chen
  2015-01-06 19:30 ` Peter Zijlstra
  2015-01-16  1:58 ` Steven Rostedt
  0 siblings, 2 replies; 10+ messages in thread
From: Tim Chen @ 2015-01-06 19:01 UTC (permalink / raw)
  To: Peter Zijlstra, Ingo Molnar
  Cc: Andi Kleen, Shawn Bohrer, Steven Rostedt, Suruchi Kadu,
	Doug Nelson, linux-kernel

Didn't get any response for this patch probably due to the holidays.
Reposting it as we will like to get it merged to help our database
workload.

This patch added checks that prevent futile attempts to move rt tasks
to 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@linux.intel.com>
---
 kernel/sched/rt.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index ee15f5a..0e4382e 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1337,7 +1337,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags)
 	     curr->prio <= p->prio)) {
 		int target = find_lowest_rq(p);
 
-		if (target != -1)
+		if (target != -1 &&
+		    p->prio < cpu_rq(target)->rt.highest_prio.curr)
 			cpu = target;
 	}
 	rcu_read_unlock();
@@ -1613,6 +1614,12 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
 			break;
 
 		lowest_rq = cpu_rq(cpu);
+		
+		if (lowest_rq->rt.highest_prio.curr <= task->prio) {
+		/* target rq has tasks of equal or higher priority, try again */
+			lowest_rq = NULL;
+			continue;
+		}
 
 		/* if the prio of this runqueue changed, try again */
 		if (double_lock_balance(rq, lowest_rq)) {
-- 
1.8.3.1



^ permalink raw reply related	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2015-04-09  1:19 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-01-06 19:01 [PATCH] Repost sched-rt: Reduce rq lock contention by eliminating locking of non-feasible target Tim Chen
2015-01-06 19:30 ` Peter Zijlstra
2015-01-15 17:13   ` Tim Chen
2015-01-16  1:58 ` Steven Rostedt
2015-01-16 17:46   ` Tim Chen
2015-01-22 17:48     ` Tim Chen
2015-02-01 17:52     ` [tip:sched/core] sched/rt: " tip-bot for Tim Chen
2015-02-24 16:12       ` Steven Rostedt
2015-03-03 21:12         ` Ben Hutchings
2015-04-09  1:17         ` Zefan Li

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