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 stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html