From: Tim Chen <tim.c.c...@linux.intel.com> 3.4.107-rc1 review patch. If anyone has any objections, please let me know.
------------------ 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.c...@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Shawn Bohrer <sboh...@rgmadvisors.com> Cc: Suruchi Kadu <suruchi.a.k...@intel.com> Cc: Doug Nelson<doug.nel...@intel.com> Cc: Steven Rostedt <rost...@goodmis.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Link: http://lkml.kernel.org/r/1421430374.2399.27.ca...@schen9-desk2.jf.intel.com Signed-off-by: Ingo Molnar <mi...@kernel.org> Signed-off-by: Zefan Li <lize...@huawei.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 526c77d..71429db 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1293,7 +1293,12 @@ 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(); @@ -1570,6 +1575,16 @@ 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)) { /* -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
