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authorTim Chen <tim.c.chen@linux.intel.com>2014-12-12 15:38:12 -0800
committerBen Hutchings <ben@decadent.org.uk>2015-03-06 00:39:19 +0000
commit985504f71bb0ca24ac647c72446cc621980aef9f (patch)
tree2cb7704ebe77dd284fa26690dd85a3ba89c0036f
parentc0a74eb2b093cd781f216306cc5a1e5825835d74 (diff)
downloadlinux-linaro-stable-985504f71bb0ca24ac647c72446cc621980aef9f.tar.gz
sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target
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@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> [bwh: Backported to 3.2: adjust filename] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
-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 f57fda7cbef0..bd4afa408686 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1067,7 +1067,12 @@ select_task_rq_rt(struct task_struct *p, int sd_flag, int flags)
(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(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)) {
/*