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authorTim Chen <tim.c.chen@linux.intel.com>2014-12-13 00:38:12 +0100
committerIngo Molnar <mingo@kernel.org>2015-01-30 19:38:49 +0100
commit80e3d87b2c5582db0ab5e39610ce3707d97ba409 (patch)
tree26ce03eb8edeebe4eca36d6be4de3c35e7494279 /kernel/sched
parentMerge branch 'sched/urgent' into sched/core (diff)
downloadlinux-80e3d87b2c5582db0ab5e39610ce3707d97ba409.tar.xz
linux-80e3d87b2c5582db0ab5e39610ce3707d97ba409.zip
sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target
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@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Shawn Bohrer <sbohrer@rgmadvisors.com> Cc: Suruchi Kadu <suruchi.a.kadu@intel.com> Cc: Doug Nelson<doug.nelson@intel.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1421430374.2399.27.camel@schen9-desk2.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/rt.c17
1 files changed, 16 insertions, 1 deletions
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 6725e3c49660..f4d4b077eba0 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1340,7 +1340,12 @@ 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)
+ /*
+ * 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();
@@ -1617,6 +1622,16 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
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)) {
/*