| From | Luis Henriques <> | Subject | [PATCH 3.16.y-ckt 181/183] sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target | Date | Fri, 6 Mar 2015 09:57:52 +0000 |
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3.16.7-ckt8 -stable review patch. If anyone has any objections, please let me know.
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From: Tim Chen <tim.c.chen@linux.intel.com>
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> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- kernel/sched/rt.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index a49083192c64..5d720ac96246 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1336,7 +1336,12 @@ 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(); @@ -1608,6 +1613,16 @@ 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)) { /*
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