linux-kernel - [PATCH] sched/rt: restore rt_runtime after disabling RT_RUNTIME

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Message-Id: <1531874815-39357-1-git-send-email-liu.hailong6@zte.com.cn>
Date:   Wed, 18 Jul 2018 08:46:55 +0800
From:   Hailong Liu <liu.hailong6@....com.cn>
To:     mingo@...hat.com, peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, jiang.biao2@....com.cn,
        zhong.weidong@....com.cn, Hailong Liu <liu.hailong6@....com.cn>
Subject: [PATCH] sched/rt: restore rt_runtime after disabling RT_RUNTIME_SHARE

NO_RT_RUNTIME_SHARE feature is used to prevent a CPU borrow enough
runtime with a spin-rt-task.

However, if RT_RUNTIME_SHARE feature is enabled and rt_rq has borrowd
enough rt_runtime at the beginning, rt_runtime can't be restored to
its initial bandwidth rt_runtime after we disable RT_RUNTIME_SHARE.

E.g. on my PC with 4 cores, procedure to reproduce:
1) Make sure  RT_RUNTIME_SHARE is enabled
 cat /sys/kernel/debug/sched_features
  GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY
  CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_DOUBLE_TICK
  LB_BIAS NONTASK_CAPACITY TTWU_QUEUE NO_SIS_AVG_CPU SIS_PROP
  NO_WARN_DOUBLE_CLOCK RT_PUSH_IPI RT_RUNTIME_SHARE NO_LB_MIN
  ATTACH_AGE_LOAD WA_IDLE WA_WEIGHT WA_BIAS
2) Start a spin-rt-task
 ./loop_rr &
3) set affinity to the last cpu
 taskset -p 8 $pid_of_loop_rr
4) Observe that last cpu have borrowed enough runtime.
 cat /proc/sched_debug | grep rt_runtime
  .rt_runtime                    : 950.000000
  .rt_runtime                    : 900.000000
  .rt_runtime                    : 950.000000
  .rt_runtime                    : 1000.000000
5) Disable RT_RUNTIME_SHARE
 echo NO_RT_RUNTIME_SHARE > /sys/kernel/debug/sched_features
6) Observe that rt_runtime can not been restored
 cat /proc/sched_debug | grep rt_runtime
  .rt_runtime                    : 950.000000
  .rt_runtime                    : 900.000000
  .rt_runtime                    : 950.000000
  .rt_runtime                    : 1000.000000

This patch help to restore rt_runtime after we disable 
RT_RUNTIME_SHARE.

Signed-off-by: Hailong Liu <liu.hailong6@....com.cn>
Signed-off-by: Jiang Biao <jiang.biao2@....com.cn>
---
 kernel/sched/rt.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 5725670..eaaec83 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -836,6 +836,8 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
 		 * can be time-consuming. Try to avoid it when possible.
 		 */
 		raw_spin_lock(&rt_rq->rt_runtime_lock);
+		if (!sched_feat(RT_RUNTIME_SHARE) && rt_rq->rt_runtime != RUNTIME_INF)
+			rt_rq->rt_runtime = rt_b->rt_runtime;
 		skip = !rt_rq->rt_time && !rt_rq->rt_nr_running;
 		raw_spin_unlock(&rt_rq->rt_runtime_lock);
 		if (skip)
-- 
2.7.4