BACKPORT: 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%.
Bug: 37474896
(@joel: One of the hunks in this patch was already applied by Srinath in
commit [1], so dropping that hunk)
[1] commit 89288d853b2a ("sched/rt: Avoid moving rt task if destination
CPU does not run low priority task.")
Signed-off-by: Joel Fernandes <joelaf@google.com>
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>
Change-Id: I80da92afed2957537e1a64b90144293f74003969
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index f3c02a5..07dd76a 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1780,6 +1780,16 @@
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)) {
/*
