[PATCH 1/2] sched: Rework migrate_tasks()

[PATCH 1/2] sched: Rework migrate_tasks()

[Kirill Tkhai]

Currently migrate_tasks() skips throttled tasks,
because they are not pickable by pick_next_task().

These tasks stay on dead cpu even after they
becomes unthrottled. They are not schedulable
till user manually changes their affinity or till
cpu becomes alive again.

But for user this looks completely untransparent:
task hangs, but it's not obvious what he has to do,
because kernel does not report any problem.

This situation may easily be triggered intentionally.
Playing with extremely small cpu.cfs_quota_us causes
it almost in 100% cases. In usual life it's very rare,
but still possible for some unhappy user.

This patch changes migrate_tasks() to iterate throw
all of the threads in the system under tasklist_lock
is locked. This may a little worsen the performance,
but:

1)it guarantees all of tasks will migrate;

2)migrate_tasks() is not performance critical,
  it just must do what it has to do.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c |   75 ++++++++++++++-------------------------------------
 1 file changed, 20 insertions(+), 55 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d0d1565..da7f4c5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4795,78 +4795,43 @@ static void calc_load_migrate(struct rq *rq)
 		atomic_long_add(delta, &calc_load_tasks);
 }
 
-static void put_prev_task_fake(struct rq *rq, struct task_struct *prev)
-{
-}
-
-static const struct sched_class fake_sched_class = {
-	.put_prev_task = put_prev_task_fake,
-};
-
-static struct task_struct fake_task = {
-	/*
-	 * Avoid pull_{rt,dl}_task()
-	 */
-	.prio = MAX_PRIO + 1,
-	.sched_class = &fake_sched_class,
-};
-
 /*
  * Migrate all tasks from the rq, sleeping tasks will be migrated by
  * try_to_wake_up()->select_task_rq().
  *
- * Called with rq->lock held even though we'er in stop_machine() and
- * there's no concurrency possible, we hold the required locks anyway
- * because of lock validation efforts.
+ * Called from stop_machine(), and there's no concurrency possible, but
+ * we hold the required locks anyway because of lock validation efforts.
  */
 static void migrate_tasks(unsigned int dead_cpu)
 {
 	struct rq *rq = cpu_rq(dead_cpu);
-	struct task_struct *next, *stop = rq->stop;
+	struct task_struct *g, *p;
 	int dest_cpu;
 
-	/*
-	 * Fudge the rq selection such that the below task selection loop
-	 * doesn't get stuck on the currently eligible stop task.
-	 *
-	 * We're currently inside stop_machine() and the rq is either stuck
-	 * in the stop_machine_cpu_stop() loop, or we're executing this code,
-	 * either way we should never end up calling schedule() until we're
-	 * done here.
-	 */
-	rq->stop = NULL;
-
-	/*
-	 * put_prev_task() and pick_next_task() sched
-	 * class method both need to have an up-to-date
-	 * value of rq->clock[_task]
-	 */
-	update_rq_clock(rq);
-
-	for ( ; ; ) {
+	read_lock(&tasklist_lock);
+	do_each_thread(g, p) {
 		/*
-		 * There's this thread running, bail when that's the only
-		 * remaining thread.
+		 * We're inside stop_machine() and nobody can manage tasks
+		 * in parallel. So, this unlocked check is correct.
 		 */
-		if (rq->nr_running == 1)
-			break;
+		if (!p->on_rq || task_cpu(p) != dead_cpu)
+			continue;
 
-		next = pick_next_task(rq, &fake_task);
-		BUG_ON(!next);
-		next->sched_class->put_prev_task(rq, next);
+		if (p == rq->stop)
+			continue;
 
 		/* Find suitable destination for @next, with force if needed. */
-		dest_cpu = select_fallback_rq(dead_cpu, next);
+		raw_spin_lock(&rq->lock);
+		dest_cpu = select_fallback_rq(dead_cpu, p);
 		raw_spin_unlock(&rq->lock);
 
-		__migrate_task(next, dead_cpu, dest_cpu);
+		WARN_ON(!__migrate_task(p, dead_cpu, dest_cpu));
 
-		raw_spin_lock(&rq->lock);
-	}
+	} while_each_thread(g, p);
+	read_unlock(&tasklist_lock);
 
-	rq->stop = stop;
+	BUG_ON(rq->nr_running != 1); /* the migration thread */
 }
-
 #endif /* CONFIG_HOTPLUG_CPU */
 
 #if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_SYSCTL)
@@ -5107,16 +5072,16 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
 
 #ifdef CONFIG_HOTPLUG_CPU
 	case CPU_DYING:
+		BUG_ON(current != rq->stop);
 		sched_ttwu_pending();
 		/* Update our root-domain */
-		raw_spin_lock_irqsave(&rq->lock, flags);
+		raw_spin_lock(&rq->lock);
 		if (rq->rd) {
 			BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
 			set_rq_offline(rq);
 		}
+		raw_spin_unlock(&rq->lock);
 		migrate_tasks(cpu);
-		BUG_ON(rq->nr_running != 1); /* the migration thread */
-		raw_spin_unlock_irqrestore(&rq->lock, flags);
 		break;
 
 	case CPU_DEAD:

Re: [PATCH 1/2] sched: Rework migrate_tasks()

[Peter Zijlstra]

[-- Attachment #1: Type: text/plain, Size: 804 bytes --]

On Wed, Jun 11, 2014 at 01:52:10PM +0400, Kirill Tkhai wrote:
> 
> Currently migrate_tasks() skips throttled tasks,
> because they are not pickable by pick_next_task().
> 
> These tasks stay on dead cpu even after they
> becomes unthrottled. They are not schedulable
> till user manually changes their affinity or till
> cpu becomes alive again.
> 
> But for user this looks completely untransparent:
> task hangs, but it's not obvious what he has to do,
> because kernel does not report any problem.
> 
> This situation may easily be triggered intentionally.
> Playing with extremely small cpu.cfs_quota_us causes
> it almost in 100% cases. In usual life it's very rare,
> but still possible for some unhappy user.
> 

How about fixing the unthrottle code to validate the affinity?

[-- Attachment #2: Type: application/pgp-signature, Size: 836 bytes --]

Re: [PATCH 1/2] sched: Rework migrate_tasks()

[Kirill Tkhai]

В Ср, 11/06/2014 в 12:57 +0200, Peter Zijlstra пишет:
> On Wed, Jun 11, 2014 at 01:52:10PM +0400, Kirill Tkhai wrote:
> > 
> > Currently migrate_tasks() skips throttled tasks,
> > because they are not pickable by pick_next_task().
> > 
> > These tasks stay on dead cpu even after they
> > becomes unthrottled. They are not schedulable
> > till user manually changes their affinity or till
> > cpu becomes alive again.
> > 
> > But for user this looks completely untransparent:
> > task hangs, but it's not obvious what he has to do,
> > because kernel does not report any problem.
> > 
> > This situation may easily be triggered intentionally.
> > Playing with extremely small cpu.cfs_quota_us causes
> > it almost in 100% cases. In usual life it's very rare,
> > but still possible for some unhappy user.
> > 
> 
> How about fixing the unthrottle code to validate the affinity?

I've begun that before, but found, it requires much more code
(three classes need this fix).

And this makes unthrottle code a little ugly (in my view).

	Kirill

Re: [PATCH 1/2] sched: Rework migrate_tasks()

[Srikar Dronamraju]

* Kirill Tkhai <ktkhai@parallels.com> [2014-06-11 13:52:10]:

> 
> Currently migrate_tasks() skips throttled tasks,
> because they are not pickable by pick_next_task().
> 

Before migrate_tasks() is called, we do call set_rq_offline(), in
migration_call().

Shouldnt this take care of unthrottling the tasks and making sure that
they can be picked by pick_next_task().

> These tasks stay on dead cpu even after they
> becomes unthrottled. They are not schedulable
> till user manually changes their affinity or till
> cpu becomes alive again.
> 

If we are still seeing tasks not being picked by pick_next_task(), then
can it probably mean that rq->rd was NULL?

-- 
Thanks and Regards
Srikar Dronamraju

Re: [PATCH 1/2] sched: Rework migrate_tasks()

[Kirill Tkhai]

11.06.2014, 15:24, "Srikar Dronamraju" <srikar@linux.vnet.ibm.com>:
> * Kirill Tkhai <ktkhai@parallels.com> [2014-06-11 13:52:10]:
>>  Currently migrate_tasks() skips throttled tasks,
>>  because they are not pickable by pick_next_task().
>
> Before migrate_tasks() is called, we do call set_rq_offline(), in
> migration_call().
>
> Shouldnt this take care of unthrottling the tasks and making sure that
> they can be picked by pick_next_task().

If we do this separate for every class, we'll have to do this 3 times.
Furthermore, deadline class does not have a list of throttled tasks.
So we'll have to the same as I did: to lock tasklist_lock and to iterate
throw all of the tasks in the system just to found deadline tasks.

>>  These tasks stay on dead cpu even after they
>>  becomes unthrottled. They are not schedulable
>>  till user manually changes their affinity or till
>>  cpu becomes alive again.
>
> If we are still seeing tasks not being picked by pick_next_task(), then
> can it probably mean that rq->rd was NULL?

Unthrottle functions dl_task_timer() and unthrottle_cfs_rq() put tasks and
queues back. They do not look at rq->rd.

do_sched_rt_period_timer() does not unthrottle dead queue at all (they
are excluded from rd).

Thanks,
Kirill

Re: [PATCH 1/2] sched: Rework migrate_tasks()

[Srikar Dronamraju]

> > * Kirill Tkhai <ktkhai@parallels.com> [2014-06-11 13:52:10]:
> >>  Currently migrate_tasks() skips throttled tasks,
> >>  because they are not pickable by pick_next_task().
> >
> > Before migrate_tasks() is called, we do call set_rq_offline(), in
> > migration_call().
> >
> > Shouldnt this take care of unthrottling the tasks and making sure that
> > they can be picked by pick_next_task().
>
> If we do this separate for every class, we'll have to do this 3 times.
> Furthermore, deadline class does not have a list of throttled tasks.
> So we'll have to the same as I did: to lock tasklist_lock and to iterate
> throw all of the tasks in the system just to found deadline tasks.
>

I think you misread my comment.

Currently migrate_task() gets called from migration_call() and in the
migration_call() before migrate_tasks(), set_rq_offline() should put
tasks back using unthrottle_cfs_rq().

So my question is: Why are these tasks not getting unthrottled
through we are calling set_rq_offline? To me set_rq_offline is
calling the actual sched class routines to do the needful.

I can understand about deadline tasks, because we don't have a deadline
But thats the only tasks that we need to fix.

> >>  These tasks stay on dead cpu even after they
> >>  becomes unthrottled. They are not schedulable
> >>  till user manually changes their affinity or till
> >>  cpu becomes alive again.
> >
> > If we are still seeing tasks not being picked by pick_next_task(), then
> > can it probably mean that rq->rd was NULL?
>
> Unthrottle functions dl_task_timer() and unthrottle_cfs_rq() put tasks and
> queues back. They do not look at rq->rd.

What I meant was only if rq->rd isn't set, then we don't call
set_rq_offline, which seems very reasonable.
--
Thanks and Regards
Srikar Dronamraju

Re: [PATCH 1/2] sched: Rework migrate_tasks()

[Kirill Tkhai]

11.06.2014, 17:15, "Srikar Dronamraju" <srikar@linux.vnet.ibm.com>:
>>>  * Kirill Tkhai <ktkhai@parallels.com> [2014-06-11 13:52:10]:
>>>>   Currently migrate_tasks() skips throttled tasks,
>>>>   because they are not pickable by pick_next_task().
>>>  Before migrate_tasks() is called, we do call set_rq_offline(), in
>>>  migration_call().
>>>
>>>  Shouldnt this take care of unthrottling the tasks and making sure that
>>>  they can be picked by pick_next_task().
>>  If we do this separate for every class, we'll have to do this 3 times.
>>  Furthermore, deadline class does not have a list of throttled tasks.
>>  So we'll have to the same as I did: to lock tasklist_lock and to iterate
>>  throw all of the tasks in the system just to found deadline tasks.
>
> I think you misread my comment.
>
> Currently migrate_task() gets called from migration_call() and in the
> migration_call() before migrate_tasks(), set_rq_offline() should put
> tasks back using unthrottle_cfs_rq().
>
> So my question is: Why are these tasks not getting unthrottled
> through we are calling set_rq_offline? To me set_rq_offline is
> calling the actual sched class routines to do the needful.
>
> I can understand about deadline tasks, because we don't have a deadline
> But thats the only tasks that we need to fix.

Hm, I tested that on fair class tasks. They used to disappear from
/proc/sched_debug and used to hang. I'll check all once again.

I'm agree with you, if set_rq_offline() already presents, we should use it.

/me went to clarify why it does not work in my test.

>>>>   These tasks stay on dead cpu even after they
>>>>   becomes unthrottled. They are not schedulable
>>>>   till user manually changes their affinity or till
>>>>   cpu becomes alive again.
>>>  If we are still seeing tasks not being picked by pick_next_task(), then
>>>  can it probably mean that rq->rd was NULL?
>>  Unthrottle functions dl_task_timer() and unthrottle_cfs_rq() put tasks and
>>  queues back. They do not look at rq->rd.
>
> What I meant was only if rq->rd isn't set, then we don't call
> set_rq_offline, which seems very reasonable.
> --
> Thanks and Regards
> Srikar Dronamraju

Re: [PATCH 1/2] sched: Rework migrate_tasks()

[Kirill Tkhai]

В Ср, 11/06/2014 в 17:43 +0400, Kirill Tkhai пишет:
> 
> 11.06.2014, 17:15, "Srikar Dronamraju" <srikar@linux.vnet.ibm.com>:
> >>>  * Kirill Tkhai <ktkhai@parallels.com> [2014-06-11 13:52:10]:
> >>>>   Currently migrate_tasks() skips throttled tasks,
> >>>>   because they are not pickable by pick_next_task().
> >>>  Before migrate_tasks() is called, we do call set_rq_offline(), in
> >>>  migration_call().
> >>>
> >>>  Shouldnt this take care of unthrottling the tasks and making sure that
> >>>  they can be picked by pick_next_task().
> >>  If we do this separate for every class, we'll have to do this 3 times.
> >>  Furthermore, deadline class does not have a list of throttled tasks.
> >>  So we'll have to the same as I did: to lock tasklist_lock and to iterate
> >>  throw all of the tasks in the system just to found deadline tasks.
> >
> > I think you misread my comment.
> >
> > Currently migrate_task() gets called from migration_call() and in the
> > migration_call() before migrate_tasks(), set_rq_offline() should put
> > tasks back using unthrottle_cfs_rq().
> >
> > So my question is: Why are these tasks not getting unthrottled
> > through we are calling set_rq_offline? To me set_rq_offline is
> > calling the actual sched class routines to do the needful.
> >
> > I can understand about deadline tasks, because we don't have a deadline
> > But thats the only tasks that we need to fix.
> 
> Hm, I tested that on fair class tasks. They used to disappear from
> /proc/sched_debug and used to hang. I'll check all once again.
> 
> I'm agree with you, if set_rq_offline() already presents, we should use it.
> 
> /me went to clarify why it does not work in my test.

Ok, it looks like the problem is that unthrottled cfs_rq may become throttled
again ;)

__migrate_task()->dequeue_task() calls update_rq_clock(), which throttles
just unthrottle cfs_rq after a first picked task is moved.

Hope, something like above helps, I'll check if there are no other problem
and write again.

---
 kernel/sched/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d0d1565..b5fd6f0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4843,6 +4843,12 @@ static void migrate_tasks(unsigned int dead_cpu)
 	 */
 	update_rq_clock(rq);
 
+	/*
+	 * Prevent rq->clock update from __migrate_task()->dequeue_task()
+	 * to do not throttle sched_class queues and tasks.
+	 */
+	rq->skip_clock_update = 1;
+
 	for ( ; ; ) {
 		/*
 		 * There's this thread running, bail when that's the only
@@ -4864,6 +4870,8 @@ static void migrate_tasks(unsigned int dead_cpu)
 		raw_spin_lock(&rq->lock);
 	}
 
+	rq->skip_clock_update = 0; /* Reset it back */
+
 	rq->stop = stop;
 }
 

Re: [PATCH 1/2] sched: Rework migrate_tasks()

[Mike Galbraith]

On Wed, 2014-06-11 at 23:33 +0400, Kirill Tkhai wrote: 
> В Ср, 11/06/2014 в 17:43 +0400, Kirill Tkhai пишет:
> > 
> > 11.06.2014, 17:15, "Srikar Dronamraju" <srikar@linux.vnet.ibm.com>:
> > >>>  * Kirill Tkhai <ktkhai@parallels.com> [2014-06-11 13:52:10]:
> > >>>>   Currently migrate_tasks() skips throttled tasks,
> > >>>>   because they are not pickable by pick_next_task().
> > >>>  Before migrate_tasks() is called, we do call set_rq_offline(), in
> > >>>  migration_call().
> > >>>
> > >>>  Shouldnt this take care of unthrottling the tasks and making sure that
> > >>>  they can be picked by pick_next_task().
> > >>  If we do this separate for every class, we'll have to do this 3 times.
> > >>  Furthermore, deadline class does not have a list of throttled tasks.
> > >>  So we'll have to the same as I did: to lock tasklist_lock and to iterate
> > >>  throw all of the tasks in the system just to found deadline tasks.
> > >
> > > I think you misread my comment.
> > >
> > > Currently migrate_task() gets called from migration_call() and in the
> > > migration_call() before migrate_tasks(), set_rq_offline() should put
> > > tasks back using unthrottle_cfs_rq().
> > >
> > > So my question is: Why are these tasks not getting unthrottled
> > > through we are calling set_rq_offline? To me set_rq_offline is
> > > calling the actual sched class routines to do the needful.
> > >
> > > I can understand about deadline tasks, because we don't have a deadline
> > > But thats the only tasks that we need to fix.
> > 
> > Hm, I tested that on fair class tasks. They used to disappear from
> > /proc/sched_debug and used to hang. I'll check all once again.
> > 
> > I'm agree with you, if set_rq_offline() already presents, we should use it.
> > 
> > /me went to clarify why it does not work in my test.
> 
> Ok, it looks like the problem is that unthrottled cfs_rq may become throttled
> again ;)

Dejavu.  You could try either of the below.

On Thu, Apr 03, 2014 at 10:02:18AM +0200, Mike Galbraith wrote:
> Prevent large wakeup latencies from being accounted to the wrong task.
> 
> Cc: <stable@vger.kernel.org>
> Signed-off-by: 	Mike Galbraith <umgwanakikbuti@gmail.com>
> ---
>  kernel/sched/core.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -118,7 +118,12 @@ void update_rq_clock(struct rq *rq)
>  {
>  	s64 delta;
>  
> -	if (rq->skip_clock_update > 0)
> +	/*
> +	 * Set during wakeup to indicate we are on the way to schedule().
> +	 * Decrement to ensure that a very large latency is not accounted
> +	 * to the wrong task.
> +	 */
> +	if (rq->skip_clock_update-- > 0)
>  		return;
>  
>  	delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;

OK; so as previously mentioned (Oct '13); I've entirely had it with
skip_clock_update bugs, so I got angry and did the below.

Its not something I can merge, not least because it uses trace_printk(),
but it should be usable to 1) demonstate the above actually helps and 2)
make damn sure we got it right this time :-)

I've not really stared at the output much yet; but when you select
function_graph tracer; we get lovely things like:

  8)               |                                          wake_up_process() {
  8)               |                                            try_to_wake_up() {
  8)   0.076 us    |                                              _raw_spin_lock_irqsave();
  8)   0.092 us    |                                              task_waking_fair();
  8)   0.106 us    |                                              select_task_rq_fair();
  8)   0.161 us    |                                              _raw_spin_lock();
  8)               |                                              ttwu_do_activate.constprop.103() {
  8)               |                                                activate_task() {
  8)               |                                                  enqueue_task() {
  8)               |                                                    update_rq_clock() {
  8)               |                                                      /* clock update: 420411 */
  8)   0.084 us    |                                                      sched_avg_update();
  8)   1.277 us    |                                                    }
  8)               |                                                    enqueue_task_fair() {
  8)               |                                                      enqueue_entity() {
  8)   0.083 us    |                                                        update_curr();
  8)   0.071 us    |                                                        __compute_runnable_contrib();
  8)   0.074 us    |                                                        __update_entity_load_avg_contrib();
  8)   0.121 us    |                                                        update_cfs_rq_blocked_load();
  8)   0.236 us    |                                                        account_entity_enqueue();
  8)   0.076 us    |                                                        update_cfs_shares();
  8)   0.075 us    |                                                        place_entity();
  8)   0.123 us    |                                                        __enqueue_entity();
  8)   5.260 us    |                                                      }
  8)   0.069 us    |                                                      __compute_runnable_contrib();
  8)   0.073 us    |                                                      hrtick_update();
  8)   7.146 us    |                                                    }
  8)   9.583 us    |                                                  }
  8) + 10.169 us   |                                                }
  8)               |                                                wq_worker_waking_up() {
  8)   0.071 us    |                                                  kthread_data();
  8)   0.682 us    |                                                }
  8)               |                                                ttwu_do_wakeup() {
  8)               |                                                  check_preempt_curr() {
  8)   0.077 us    |                                                    resched_task();
  8)               |                                                    /* skip_clock_update on cpu: 8 */
  8)   1.188 us    |                                                  }
  8)   1.914 us    |                                                }
  8) + 14.533 us   |                                              }
  8)   0.071 us    |                                              _raw_spin_unlock();
  8)   0.082 us    |                                              _raw_spin_unlock_irqrestore();
  8) + 18.874 us   |                                            }
  8) + 19.509 us   |                                          }

...

  8)               |                                          wake_up_process() {
  8)               |                                            try_to_wake_up() {
  8)   0.101 us    |                                              _raw_spin_lock_irqsave();
  8)   0.089 us    |                                              task_waking_fair();
  8)   0.071 us    |                                              select_task_rq_fair();
  8)   0.070 us    |                                              _raw_spin_lock();
  8)               |                                              ttwu_do_activate.constprop.103() {
  8)               |                                                activate_task() {
  8)               |                                                  enqueue_task() {
  8)               |                                                    update_rq_clock() {
  8)               |                                                      /* Invalid clock skip on cpu: 8 */
  8)               |                                                      /* clock update: 420413 */
  8)   0.942 us    |                                                    }
  8)               |                                                    enqueue_task_fair() {
  8)               |                                                      enqueue_entity() {
  8)   0.081 us    |                                                        update_curr();
  8)   0.074 us    |                                                        __compute_runnable_contrib();
  8)   0.069 us    |                                                        __update_entity_load_avg_contrib();
  8)   0.091 us    |                                                        update_cfs_rq_blocked_load();
  8)   0.108 us    |                                                        account_entity_enqueue();
  8)   0.081 us    |                                                        update_cfs_shares();
  8)   0.069 us    |                                                        place_entity();
  8)   0.107 us    |                                                        __enqueue_entity();
  8)   5.120 us    |                                                      }
  8)   0.068 us    |                                                      hrtick_update();
  8)   6.410 us    |                                                    }
  8)   8.484 us    |                                                  }
  8)   9.045 us    |                                                }
  8)               |                                                wq_worker_waking_up() {
  8)   0.074 us    |                                                  kthread_data();
  8)   0.669 us    |                                                }
  8)               |                                                ttwu_do_wakeup() {
  8)               |                                                  check_preempt_curr() {
  8)   0.091 us    |                                                    resched_task();
  8)               |                                                    /* skip_clock_update on cpu: 8 */
  8)   1.080 us    |                                                  }
  8)   1.709 us    |                                                }
  8) + 13.007 us   |                                              }
  8)   0.071 us    |                                              _raw_spin_unlock();
  8)   0.090 us    |                                              _raw_spin_unlock_irqrestore();
  8) + 17.105 us   |                                            }
  8) + 17.702 us   |                                          }

...

  8)               |  schedule_preempt_disabled() {
  8)               |    schedule() {
  8)               |    __schedule() {
  8)   0.105 us    |      rcu_note_context_switch();
  8)   0.078 us    |      _raw_spin_lock();
  8)               |      update_rq_clock() {
  8)               |        /* Invalid clock skip on cpu: 8 */
  8)               |        /* clock update: 420415 */
  8)   0.073 us    |        sched_avg_update();
  8)   1.630 us    |      }
  8)   0.080 us    |      pick_next_task_stop();
  8)   0.112 us    |      pick_next_task_dl();
  8)   0.088 us    |      pick_next_task_rt();
  8)               |      pick_next_task_fair() {
  8)               |        put_prev_task_idle() {
  8)   0.118 us    |          idle_exit_fair();
  8)   0.709 us    |        }
  8)               |        pick_next_entity() {
  8)   0.071 us    |          clear_buddies();
  8)   0.721 us    |        }
  8)               |        set_next_entity() {
  8)   0.139 us    |          __dequeue_entity();
  8)   0.732 us    |        }
  8)   3.804 us    |      }
 ------------------------------------------
  8)    <idle>-0    =>   <...>-220   
 ------------------------------------------

  8)               |      finish_task_switch() {
  8)   0.076 us    |        _raw_spin_unlock();
  8)   0.716 us    |      }
  8) ! 1876.643 us |    }
  8) ! 1877.297 us |  } /* schedule */

Also; did I say how much I hate that function_graph doesn't default to
latency-format ?

---
 kernel/sched/core.c      |  130 +++++++++++++++++++++++++++++------------------
 kernel/sched/deadline.c  |    6 +-
 kernel/sched/debug.c     |    7 +-
 kernel/sched/fair.c      |   50 ++++++++++--------
 kernel/sched/idle_task.c |    4 -
 kernel/sched/proc.c      |    4 -
 kernel/sched/rt.c        |    4 -
 kernel/sched/sched.h     |  105 ++++++++++++++++++++++---------------
 lib/Kconfig.debug        |    7 ++
 9 files changed, 195 insertions(+), 122 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -135,11 +135,31 @@ void update_rq_clock(struct rq *rq)
 {
 	s64 delta;
 
+#ifdef CONFIG_SCHED_DEBUG_CLOCK
+	if (rq->skip_clock_update > 0 && rq->clock_stamp != rq->clock_seq) {
+		rq->skip_clock_update = 0;
+		trace_printk("Invalid clock skip on cpu: %d\n", rq->cpu);
+		goto do_update;
+	}
+#endif
+
 	if (rq->skip_clock_update > 0)
 		return;
 
-	delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
-	rq->clock += delta;
+#ifdef CONFIG_SCHED_DEBUG_CLOCK
+	if (!(rq->clock_stamp & 1))
+		trace_printk("clock update outside of rq->lock\n");
+
+	if (rq->clock_stamp == rq->clock_seq)
+		trace_printk("superfluous clock update\n");
+
+do_update:
+	trace_printk("clock update: %u\n", rq->clock_seq);
+	rq->clock_stamp = rq->clock_seq;
+#endif
+
+	delta = sched_clock_cpu(cpu_of(rq)) - rq->__clock;
+	rq->__clock += delta;
 	update_rq_clock_task(rq, delta);
 }
 
@@ -325,10 +345,10 @@ static inline struct rq *__task_rq_lock(
 
 	for (;;) {
 		rq = task_rq(p);
-		raw_spin_lock(&rq->lock);
+		rq_lock(rq);
 		if (likely(rq == task_rq(p)))
 			return rq;
-		raw_spin_unlock(&rq->lock);
+		rq_unlock(rq);
 	}
 }
 
@@ -344,10 +364,10 @@ static struct rq *task_rq_lock(struct ta
 	for (;;) {
 		raw_spin_lock_irqsave(&p->pi_lock, *flags);
 		rq = task_rq(p);
-		raw_spin_lock(&rq->lock);
+		rq_lock(rq);
 		if (likely(rq == task_rq(p)))
 			return rq;
-		raw_spin_unlock(&rq->lock);
+		rq_unlock(rq);
 		raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
 	}
 }
@@ -355,7 +375,7 @@ static struct rq *task_rq_lock(struct ta
 static void __task_rq_unlock(struct rq *rq)
 	__releases(rq->lock)
 {
-	raw_spin_unlock(&rq->lock);
+	rq_unlock(rq);
 }
 
 static inline void
@@ -363,7 +383,7 @@ task_rq_unlock(struct rq *rq, struct tas
 	__releases(rq->lock)
 	__releases(p->pi_lock)
 {
-	raw_spin_unlock(&rq->lock);
+	rq_unlock(rq);
 	raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
 }
 
@@ -377,7 +397,7 @@ static struct rq *this_rq_lock(void)
 
 	local_irq_disable();
 	rq = this_rq();
-	raw_spin_lock(&rq->lock);
+	rq_lock(rq);
 
 	return rq;
 }
@@ -403,10 +423,10 @@ static enum hrtimer_restart hrtick(struc
 
 	WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
 
-	raw_spin_lock(&rq->lock);
+	rq_lock(rq);
 	update_rq_clock(rq);
 	rq->curr->sched_class->task_tick(rq, rq->curr, 1);
-	raw_spin_unlock(&rq->lock);
+	rq_unlock(rq);
 
 	return HRTIMER_NORESTART;
 }
@@ -428,10 +448,10 @@ static void __hrtick_start(void *arg)
 {
 	struct rq *rq = arg;
 
-	raw_spin_lock(&rq->lock);
+	rq_lock(rq);
 	__hrtick_restart(rq);
 	rq->hrtick_csd_pending = 0;
-	raw_spin_unlock(&rq->lock);
+	rq_unlock(rq);
 }
 
 /*
@@ -565,7 +585,7 @@ void resched_task(struct task_struct *p)
 {
 	int cpu;
 
-	lockdep_assert_held(&task_rq(p)->lock);
+	lockdep_assert_held(&task_rq(p)->__lock);
 
 	if (test_tsk_need_resched(p))
 		return;
@@ -587,10 +607,10 @@ void resched_cpu(int cpu)
 	struct rq *rq = cpu_rq(cpu);
 	unsigned long flags;
 
-	if (!raw_spin_trylock_irqsave(&rq->lock, flags))
+	if (!raw_spin_trylock_irqsave(&rq->__lock, flags))
 		return;
 	resched_task(cpu_curr(cpu));
-	raw_spin_unlock_irqrestore(&rq->lock, flags);
+	raw_spin_unlock_irqrestore(&rq->__lock, flags);
 }
 
 #ifdef CONFIG_SMP
@@ -893,7 +913,7 @@ static void update_rq_clock_task(struct
 	}
 #endif
 
-	rq->clock_task += delta;
+	rq->__clock_task += delta;
 
 #if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
 	if ((irq_delta + steal) && sched_feat(NONTASK_POWER))
@@ -1023,8 +1043,10 @@ void check_preempt_curr(struct rq *rq, s
 	 * A queue event has occurred, and we're going to schedule.  In
 	 * this case, we can save a useless back to back clock update.
 	 */
-	if (rq->curr->on_rq && test_tsk_need_resched(rq->curr))
+	if (rq->curr->on_rq && test_tsk_need_resched(rq->curr)) {
+		trace_printk("skip_clock_update on cpu: %d\n", rq->cpu);
 		rq->skip_clock_update = 1;
+	}
 }
 
 #ifdef CONFIG_SMP
@@ -1535,7 +1557,7 @@ static void sched_ttwu_pending(void)
 	struct llist_node *llist = llist_del_all(&rq->wake_list);
 	struct task_struct *p;
 
-	raw_spin_lock(&rq->lock);
+	rq_lock(rq);
 
 	while (llist) {
 		p = llist_entry(llist, struct task_struct, wake_entry);
@@ -1543,7 +1565,7 @@ static void sched_ttwu_pending(void)
 		ttwu_do_activate(rq, p, 0);
 	}
 
-	raw_spin_unlock(&rq->lock);
+	rq_unlock(rq);
 }
 
 void scheduler_ipi(void)
@@ -1611,9 +1633,9 @@ static void ttwu_queue(struct task_struc
 	}
 #endif
 
-	raw_spin_lock(&rq->lock);
+	rq_lock(rq);
 	ttwu_do_activate(rq, p, 0);
-	raw_spin_unlock(&rq->lock);
+	rq_unlock(rq);
 }
 
 /**
@@ -1704,12 +1726,12 @@ static void try_to_wake_up_local(struct
 	    WARN_ON_ONCE(p == current))
 		return;
 
-	lockdep_assert_held(&rq->lock);
+	lockdep_assert_held(&rq->__lock);
 
 	if (!raw_spin_trylock(&p->pi_lock)) {
-		raw_spin_unlock(&rq->lock);
+		raw_spin_unlock(&rq->__lock);
 		raw_spin_lock(&p->pi_lock);
-		raw_spin_lock(&rq->lock);
+		raw_spin_lock(&rq->__lock);
 	}
 
 	if (!(p->state & TASK_NORMAL))
@@ -2226,10 +2248,12 @@ static inline void post_schedule(struct
 	if (rq->post_schedule) {
 		unsigned long flags;
 
-		raw_spin_lock_irqsave(&rq->lock, flags);
+		local_irq_save(flags);
+		rq_lock(rq);
 		if (rq->curr->sched_class->post_schedule)
 			rq->curr->sched_class->post_schedule(rq);
-		raw_spin_unlock_irqrestore(&rq->lock, flags);
+		rq_unlock(rq);
+		local_irq_restore(flags);
 
 		rq->post_schedule = 0;
 	}
@@ -2479,11 +2503,11 @@ void scheduler_tick(void)
 
 	sched_clock_tick();
 
-	raw_spin_lock(&rq->lock);
+	rq_lock(rq);
 	update_rq_clock(rq);
 	curr->sched_class->task_tick(rq, curr, 0);
 	update_cpu_load_active(rq);
-	raw_spin_unlock(&rq->lock);
+	rq_unlock(rq);
 
 	perf_event_task_tick();
 
@@ -2732,7 +2756,8 @@ static void __sched __schedule(void)
 	 * done by the caller to avoid the race with signal_wake_up().
 	 */
 	smp_mb__before_spinlock();
-	raw_spin_lock_irq(&rq->lock);
+	local_irq_disable();
+	rq_lock(rq);
 
 	switch_count = &prev->nivcsw;
 	if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
@@ -2780,8 +2805,10 @@ static void __sched __schedule(void)
 		 */
 		cpu = smp_processor_id();
 		rq = cpu_rq(cpu);
-	} else
-		raw_spin_unlock_irq(&rq->lock);
+	} else {
+		rq_unlock(rq);
+		local_irq_enable();
+	}
 
 	post_schedule(rq);
 
@@ -4106,9 +4133,8 @@ SYSCALL_DEFINE0(sched_yield)
 	 * Since we are going to call schedule() anyway, there's
 	 * no need to preempt or enable interrupts:
 	 */
-	__release(rq->lock);
-	spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
-	do_raw_spin_unlock(&rq->lock);
+	preempt_disable();
+	rq_unlock(rq);
 	sched_preempt_enable_no_resched();
 
 	schedule();
@@ -4510,7 +4536,8 @@ void init_idle(struct task_struct *idle,
 	struct rq *rq = cpu_rq(cpu);
 	unsigned long flags;
 
-	raw_spin_lock_irqsave(&rq->lock, flags);
+	local_irq_save(flags);
+	rq_lock(rq);
 
 	__sched_fork(0, idle);
 	idle->state = TASK_RUNNING;
@@ -4536,7 +4563,8 @@ void init_idle(struct task_struct *idle,
 #if defined(CONFIG_SMP)
 	idle->on_cpu = 1;
 #endif
-	raw_spin_unlock_irqrestore(&rq->lock, flags);
+	rq_unlock(rq);
+	local_irq_restore(flags);
 
 	/* Set the preempt count _outside_ the spinlocks! */
 	init_idle_preempt_count(idle, cpu);
@@ -4835,11 +4863,11 @@ static void migrate_tasks(unsigned int d
 
 		/* Find suitable destination for @next, with force if needed. */
 		dest_cpu = select_fallback_rq(dead_cpu, next);
-		raw_spin_unlock(&rq->lock);
+		rq_unlock(rq);
 
 		__migrate_task(next, dead_cpu, dest_cpu);
 
-		raw_spin_lock(&rq->lock);
+		rq_lock(rq);
 	}
 
 	rq->stop = stop;
@@ -5100,27 +5128,31 @@ migration_call(struct notifier_block *nf
 
 	case CPU_ONLINE:
 		/* Update our root-domain */
-		raw_spin_lock_irqsave(&rq->lock, flags);
+		local_irq_save(flags);
+		rq_lock(rq);
 		if (rq->rd) {
 			BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
 
 			set_rq_online(rq);
 		}
-		raw_spin_unlock_irqrestore(&rq->lock, flags);
+		rq_unlock(rq);
+		local_irq_restore(flags);
 		break;
 
 #ifdef CONFIG_HOTPLUG_CPU
 	case CPU_DYING:
 		sched_ttwu_pending();
 		/* Update our root-domain */
-		raw_spin_lock_irqsave(&rq->lock, flags);
+		local_irq_save(flags);
+		rq_lock(rq);
 		if (rq->rd) {
 			BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
 			set_rq_offline(rq);
 		}
 		migrate_tasks(cpu);
 		BUG_ON(rq->nr_running != 1); /* the migration thread */
-		raw_spin_unlock_irqrestore(&rq->lock, flags);
+		rq_unlock(rq);
+		local_irq_restore(flags);
 		break;
 
 	case CPU_DEAD:
@@ -5427,7 +5459,8 @@ static void rq_attach_root(struct rq *rq
 	struct root_domain *old_rd = NULL;
 	unsigned long flags;
 
-	raw_spin_lock_irqsave(&rq->lock, flags);
+	local_irq_save(flags);
+	rq_lock(rq);
 
 	if (rq->rd) {
 		old_rd = rq->rd;
@@ -5453,7 +5486,8 @@ static void rq_attach_root(struct rq *rq
 	if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
 		set_rq_online(rq);
 
-	raw_spin_unlock_irqrestore(&rq->lock, flags);
+	rq_unlock(rq);
+	local_irq_restore(flags);
 
 	if (old_rd)
 		call_rcu_sched(&old_rd->rcu, free_rootdomain);
@@ -6931,7 +6965,7 @@ void __init sched_init(void)
 		struct rq *rq;
 
 		rq = cpu_rq(i);
-		raw_spin_lock_init(&rq->lock);
+		raw_spin_lock_init(&rq->__lock);
 		rq->nr_running = 0;
 		rq->calc_load_active = 0;
 		rq->calc_load_update = jiffies + LOAD_FREQ;
@@ -7842,13 +7876,13 @@ static int tg_set_cfs_bandwidth(struct t
 		struct cfs_rq *cfs_rq = tg->cfs_rq[i];
 		struct rq *rq = cfs_rq->rq;
 
-		raw_spin_lock_irq(&rq->lock);
+		raw_spin_lock_irq(&rq->__lock);
 		cfs_rq->runtime_enabled = runtime_enabled;
 		cfs_rq->runtime_remaining = 0;
 
 		if (cfs_rq->throttled)
 			unthrottle_cfs_rq(cfs_rq);
-		raw_spin_unlock_irq(&rq->lock);
+		raw_spin_unlock_irq(&rq->__lock);
 	}
 	if (runtime_was_enabled && !runtime_enabled)
 		cfs_bandwidth_usage_dec();
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -511,11 +511,11 @@ static enum hrtimer_restart dl_task_time
 	struct rq *rq;
 again:
 	rq = task_rq(p);
-	raw_spin_lock(&rq->lock);
+	rq_lock(rq);
 
 	if (rq != task_rq(p)) {
 		/* Task was moved, retrying. */
-		raw_spin_unlock(&rq->lock);
+		rq_unlock(rq);
 		goto again;
 	}
 
@@ -548,7 +548,7 @@ static enum hrtimer_restart dl_task_time
 #endif
 	}
 unlock:
-	raw_spin_unlock(&rq->lock);
+	rq_unlock(rq);
 
 	return HRTIMER_NORESTART;
 }
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -187,7 +187,7 @@ void print_cfs_rq(struct seq_file *m, in
 	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "exec_clock",
 			SPLIT_NS(cfs_rq->exec_clock));
 
-	raw_spin_lock_irqsave(&rq->lock, flags);
+	raw_spin_lock_irqsave(&rq->__lock, flags);
 	if (cfs_rq->rb_leftmost)
 		MIN_vruntime = (__pick_first_entity(cfs_rq))->vruntime;
 	last = __pick_last_entity(cfs_rq);
@@ -195,7 +195,7 @@ void print_cfs_rq(struct seq_file *m, in
 		max_vruntime = last->vruntime;
 	min_vruntime = cfs_rq->min_vruntime;
 	rq0_min_vruntime = cpu_rq(0)->cfs.min_vruntime;
-	raw_spin_unlock_irqrestore(&rq->lock, flags);
+	raw_spin_unlock_irqrestore(&rq->__lock, flags);
 	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "MIN_vruntime",
 			SPLIT_NS(MIN_vruntime));
 	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "min_vruntime",
@@ -301,7 +301,8 @@ do {									\
 	P(nr_uninterruptible);
 	PN(next_balance);
 	SEQ_printf(m, "  .%-30s: %ld\n", "curr->pid", (long)(task_pid_nr(rq->curr)));
-	PN(clock);
+	PN(__clock);
+	PN(__clock_task);
 	P(cpu_load[0]);
 	P(cpu_load[1]);
 	P(cpu_load[2]);
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3421,7 +3421,7 @@ static u64 distribute_cfs_runtime(struct
 				throttled_list) {
 		struct rq *rq = rq_of(cfs_rq);
 
-		raw_spin_lock(&rq->lock);
+		raw_spin_lock(&rq->__lock);
 		if (!cfs_rq_throttled(cfs_rq))
 			goto next;
 
@@ -3438,7 +3438,7 @@ static u64 distribute_cfs_runtime(struct
 			unthrottle_cfs_rq(cfs_rq);
 
 next:
-		raw_spin_unlock(&rq->lock);
+		raw_spin_unlock(&rq->__lock);
 
 		if (!remaining)
 			break;
@@ -4901,7 +4901,8 @@ static void yield_task_fair(struct rq *r
 		 * so we don't do microscopic update in schedule()
 		 * and double the fastpath cost.
 		 */
-		 rq->skip_clock_update = 1;
+		trace_printk("skip_clock_update on cpu: %d\n", rq->cpu);
+		rq->skip_clock_update = 1;
 	}
 
 	set_skip_buddy(se);
@@ -5446,7 +5447,8 @@ static void update_blocked_averages(int
 	struct cfs_rq *cfs_rq;
 	unsigned long flags;
 
-	raw_spin_lock_irqsave(&rq->lock, flags);
+	local_irq_save(flags);
+	rq_lock(rq);
 	update_rq_clock(rq);
 	/*
 	 * Iterates the task_group tree in a bottom up fashion, see
@@ -5461,7 +5463,8 @@ static void update_blocked_averages(int
 		__update_blocked_averages_cpu(cfs_rq->tg, rq->cpu);
 	}
 
-	raw_spin_unlock_irqrestore(&rq->lock, flags);
+	rq_unlock(rq);
+	local_irq_restore(flags);
 }
 
 /*
@@ -6641,7 +6644,7 @@ static int load_balance(int this_cpu, st
 			sd->nr_balance_failed++;
 
 		if (need_active_balance(&env)) {
-			raw_spin_lock_irqsave(&busiest->lock, flags);
+			raw_spin_lock_irqsave(&busiest->__lock, flags);
 
 			/* don't kick the active_load_balance_cpu_stop,
 			 * if the curr task on busiest cpu can't be
@@ -6649,7 +6652,7 @@ static int load_balance(int this_cpu, st
 			 */
 			if (!cpumask_test_cpu(this_cpu,
 					tsk_cpus_allowed(busiest->curr))) {
-				raw_spin_unlock_irqrestore(&busiest->lock,
+				raw_spin_unlock_irqrestore(&busiest->__lock,
 							    flags);
 				env.flags |= LBF_ALL_PINNED;
 				goto out_one_pinned;
@@ -6665,7 +6668,7 @@ static int load_balance(int this_cpu, st
 				busiest->push_cpu = this_cpu;
 				active_balance = 1;
 			}
-			raw_spin_unlock_irqrestore(&busiest->lock, flags);
+			raw_spin_unlock_irqrestore(&busiest->__lock, flags);
 
 			if (active_balance) {
 				stop_one_cpu_nowait(cpu_of(busiest),
@@ -6775,7 +6778,7 @@ static int idle_balance(struct rq *this_
 	/*
 	 * Drop the rq->lock, but keep IRQ/preempt disabled.
 	 */
-	raw_spin_unlock(&this_rq->lock);
+	raw_spin_unlock(&this_rq->__lock);
 
 	update_blocked_averages(this_cpu);
 	rcu_read_lock();
@@ -6816,7 +6819,7 @@ static int idle_balance(struct rq *this_
 	}
 	rcu_read_unlock();
 
-	raw_spin_lock(&this_rq->lock);
+	raw_spin_lock(&this_rq->__lock);
 
 	if (curr_cost > this_rq->max_idle_balance_cost)
 		this_rq->max_idle_balance_cost = curr_cost;
@@ -6860,7 +6863,7 @@ static int active_load_balance_cpu_stop(
 	struct rq *target_rq = cpu_rq(target_cpu);
 	struct sched_domain *sd;
 
-	raw_spin_lock_irq(&busiest_rq->lock);
+	raw_spin_lock_irq(&busiest_rq->__lock);
 
 	/* make sure the requested cpu hasn't gone down in the meantime */
 	if (unlikely(busiest_cpu != smp_processor_id() ||
@@ -6910,7 +6913,7 @@ static int active_load_balance_cpu_stop(
 	double_unlock_balance(busiest_rq, target_rq);
 out_unlock:
 	busiest_rq->active_balance = 0;
-	raw_spin_unlock_irq(&busiest_rq->lock);
+	raw_spin_unlock_irq(&busiest_rq->__lock);
 	return 0;
 }
 
@@ -7192,10 +7195,12 @@ static void nohz_idle_balance(struct rq
 
 		rq = cpu_rq(balance_cpu);
 
-		raw_spin_lock_irq(&rq->lock);
+		local_irq_disable();
+		rq_lock(rq);
 		update_rq_clock(rq);
 		update_idle_cpu_load(rq);
-		raw_spin_unlock_irq(&rq->lock);
+		rq_unlock(rq);
+		local_irq_enable();
 
 		rebalance_domains(rq, CPU_IDLE);
 
@@ -7359,7 +7364,8 @@ static void task_fork_fair(struct task_s
 	struct rq *rq = this_rq();
 	unsigned long flags;
 
-	raw_spin_lock_irqsave(&rq->lock, flags);
+	local_irq_save(flags);
+	rq_lock(rq);
 
 	update_rq_clock(rq);
 
@@ -7393,7 +7399,8 @@ static void task_fork_fair(struct task_s
 
 	se->vruntime -= cfs_rq->min_vruntime;
 
-	raw_spin_unlock_irqrestore(&rq->lock, flags);
+	rq_unlock(rq);
+	local_irq_restore(flags);
 }
 
 /*
@@ -7634,9 +7641,9 @@ void unregister_fair_sched_group(struct
 	if (!tg->cfs_rq[cpu]->on_list)
 		return;
 
-	raw_spin_lock_irqsave(&rq->lock, flags);
+	raw_spin_lock_irqsave(&rq->__lock, flags);
 	list_del_leaf_cfs_rq(tg->cfs_rq[cpu]);
-	raw_spin_unlock_irqrestore(&rq->lock, flags);
+	raw_spin_unlock_irqrestore(&rq->__lock, flags);
 }
 
 void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
@@ -7696,13 +7703,16 @@ int sched_group_set_shares(struct task_g
 
 		se = tg->se[i];
 		/* Propagate contribution to hierarchy */
-		raw_spin_lock_irqsave(&rq->lock, flags);
+		local_irq_save(flags);
+		rq_lock(rq);
 
 		/* Possible calls to update_curr() need rq clock */
 		update_rq_clock(rq);
 		for_each_sched_entity(se)
 			update_cfs_shares(group_cfs_rq(se));
-		raw_spin_unlock_irqrestore(&rq->lock, flags);
+
+		rq_unlock(rq);
+		local_irq_restore(flags);
 	}
 
 done:
--- a/kernel/sched/idle_task.c
+++ b/kernel/sched/idle_task.c
@@ -39,10 +39,10 @@ pick_next_task_idle(struct rq *rq, struc
 static void
 dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
 {
-	raw_spin_unlock_irq(&rq->lock);
+	raw_spin_unlock_irq(&rq->__lock);
 	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
 	dump_stack();
-	raw_spin_lock_irq(&rq->lock);
+	raw_spin_lock_irq(&rq->__lock);
 }
 
 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
--- a/kernel/sched/proc.c
+++ b/kernel/sched/proc.c
@@ -561,7 +561,7 @@ void update_cpu_load_nohz(void)
 	if (curr_jiffies == this_rq->last_load_update_tick)
 		return;
 
-	raw_spin_lock(&this_rq->lock);
+	raw_spin_lock(&this_rq->__lock);
 	pending_updates = curr_jiffies - this_rq->last_load_update_tick;
 	if (pending_updates) {
 		this_rq->last_load_update_tick = curr_jiffies;
@@ -571,7 +571,7 @@ void update_cpu_load_nohz(void)
 		 */
 		__update_cpu_load(this_rq, 0, pending_updates);
 	}
-	raw_spin_unlock(&this_rq->lock);
+	raw_spin_unlock(&this_rq->__lock);
 }
 #endif /* CONFIG_NO_HZ */
 
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -813,7 +813,7 @@ static int do_sched_rt_period_timer(stru
 		struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);
 		struct rq *rq = rq_of_rt_rq(rt_rq);
 
-		raw_spin_lock(&rq->lock);
+		rq_lock(rq);
 		if (rt_rq->rt_time) {
 			u64 runtime;
 
@@ -846,7 +846,7 @@ static int do_sched_rt_period_timer(stru
 
 		if (enqueue)
 			sched_rt_rq_enqueue(rt_rq);
-		raw_spin_unlock(&rq->lock);
+		rq_unlock(rq);
 	}
 
 	if (!throttled && (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF))
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -507,7 +507,7 @@ extern struct root_domain def_root_domai
  */
 struct rq {
 	/* runqueue lock: */
-	raw_spinlock_t lock;
+	raw_spinlock_t __lock;
 
 	/*
 	 * nr_running and cpu_load should be in the same cacheline because
@@ -528,7 +528,6 @@ struct rq {
 #ifdef CONFIG_NO_HZ_FULL
 	unsigned long last_sched_tick;
 #endif
-	int skip_clock_update;
 
 	/* capture load from *all* tasks on this cpu: */
 	struct load_weight load;
@@ -558,8 +557,11 @@ struct rq {
 	unsigned long next_balance;
 	struct mm_struct *prev_mm;
 
-	u64 clock;
-	u64 clock_task;
+	unsigned int clock_seq;
+	unsigned int clock_stamp;
+	int skip_clock_update;
+	u64 __clock;
+	u64 __clock_task;
 
 	atomic_t nr_iowait;
 
@@ -635,6 +637,24 @@ struct rq {
 #endif
 };
 
+static inline void rq_lock(struct rq *rq)
+{
+	raw_spin_lock(&rq->__lock);
+#ifdef CONFIG_SCHED_DEBUG_CLOCK
+	rq->clock_seq++;
+	barrier();
+#endif
+}
+
+static inline void rq_unlock(struct rq *rq)
+{
+#ifdef CONFIG_SCHED_DEBUG_CLOCK
+	barrier();
+	rq->clock_seq++;
+#endif
+	raw_spin_unlock(&rq->__lock);
+}
+
 static inline int cpu_of(struct rq *rq)
 {
 #ifdef CONFIG_SMP
@@ -654,12 +674,26 @@ DECLARE_PER_CPU(struct rq, runqueues);
 
 static inline u64 rq_clock(struct rq *rq)
 {
-	return rq->clock;
+#ifdef CONFIG_SCHED_DEBUG_CLOCK
+	if (rq->clock_stamp != rq->clock_seq) {
+		trace_printk("reading invalid rq->clock: %u != %u\n",
+				rq->clock_stamp, rq->clock_seq);
+	}
+#endif
+
+	return rq->__clock;
 }
 
 static inline u64 rq_clock_task(struct rq *rq)
 {
-	return rq->clock_task;
+#ifdef CONFIG_SCHED_DEBUG_CLOCK
+	if (rq->clock_stamp != rq->clock_seq) {
+		trace_printk("reading invalid rq->clock_task: %u != %u\n",
+				rq->clock_stamp, rq->clock_seq);
+	}
+#endif
+
+	return rq->__clock_task;
 }
 
 #ifdef CONFIG_NUMA_BALANCING
@@ -980,16 +1014,17 @@ static inline void finish_lock_switch(st
 #endif
 #ifdef CONFIG_DEBUG_SPINLOCK
 	/* this is a valid case when another task releases the spinlock */
-	rq->lock.owner = current;
+	rq->__lock.owner = current;
 #endif
 	/*
 	 * If we are tracking spinlock dependencies then we have to
 	 * fix up the runqueue lock - which gets 'carried over' from
 	 * prev into current:
 	 */
-	spin_acquire(&rq->lock.dep_map, 0, 0, _THIS_IP_);
+	spin_acquire(&rq->__lock.dep_map, 0, 0, _THIS_IP_);
 
-	raw_spin_unlock_irq(&rq->lock);
+	rq_unlock(rq);
+	local_irq_enable();
 }
 
 #else /* __ARCH_WANT_UNLOCKED_CTXSW */
@@ -1003,7 +1038,7 @@ static inline void prepare_lock_switch(s
 	 */
 	next->on_cpu = 1;
 #endif
-	raw_spin_unlock(&rq->lock);
+	rq_unlock(rq);
 }
 
 static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
@@ -1305,12 +1340,12 @@ static inline void double_rq_lock(struct
  * reduces latency compared to the unfair variant below.  However, it
  * also adds more overhead and therefore may reduce throughput.
  */
-static inline int _double_lock_balance(struct rq *this_rq, struct rq *busiest)
+static inline int double_lock_balance(struct rq *this_rq, struct rq *busiest)
 	__releases(this_rq->lock)
 	__acquires(busiest->lock)
 	__acquires(this_rq->lock)
 {
-	raw_spin_unlock(&this_rq->lock);
+	raw_spin_unlock(&this_rq->__lock);
 	double_rq_lock(this_rq, busiest);
 
 	return 1;
@@ -1324,22 +1359,22 @@ static inline int _double_lock_balance(s
  * grant the double lock to lower cpus over higher ids under contention,
  * regardless of entry order into the function.
  */
-static inline int _double_lock_balance(struct rq *this_rq, struct rq *busiest)
+static inline int double_lock_balance(struct rq *this_rq, struct rq *busiest)
 	__releases(this_rq->lock)
 	__acquires(busiest->lock)
 	__acquires(this_rq->lock)
 {
 	int ret = 0;
 
-	if (unlikely(!raw_spin_trylock(&busiest->lock))) {
+	if (unlikely(!raw_spin_trylock(&busiest->__lock))) {
 		if (busiest < this_rq) {
-			raw_spin_unlock(&this_rq->lock);
-			raw_spin_lock(&busiest->lock);
-			raw_spin_lock_nested(&this_rq->lock,
+			raw_spin_unlock(&this_rq->__lock);
+			raw_spin_lock(&busiest->__lock);
+			raw_spin_lock_nested(&this_rq->__lock,
 					      SINGLE_DEPTH_NESTING);
 			ret = 1;
 		} else
-			raw_spin_lock_nested(&busiest->lock,
+			raw_spin_lock_nested(&busiest->__lock,
 					      SINGLE_DEPTH_NESTING);
 	}
 	return ret;
@@ -1347,25 +1382,11 @@ static inline int _double_lock_balance(s
 
 #endif /* CONFIG_PREEMPT */
 
-/*
- * double_lock_balance - lock the busiest runqueue, this_rq is locked already.
- */
-static inline int double_lock_balance(struct rq *this_rq, struct rq *busiest)
-{
-	if (unlikely(!irqs_disabled())) {
-		/* printk() doesn't work good under rq->lock */
-		raw_spin_unlock(&this_rq->lock);
-		BUG_ON(1);
-	}
-
-	return _double_lock_balance(this_rq, busiest);
-}
-
 static inline void double_unlock_balance(struct rq *this_rq, struct rq *busiest)
 	__releases(busiest->lock)
 {
-	raw_spin_unlock(&busiest->lock);
-	lock_set_subclass(&this_rq->lock.dep_map, 0, _RET_IP_);
+	raw_spin_unlock(&busiest->__lock);
+	lock_set_subclass(&this_rq->__lock.dep_map, 0, _RET_IP_);
 }
 
 static inline void double_lock(spinlock_t *l1, spinlock_t *l2)
@@ -1407,15 +1428,15 @@ static inline void double_rq_lock(struct
 {
 	BUG_ON(!irqs_disabled());
 	if (rq1 == rq2) {
-		raw_spin_lock(&rq1->lock);
+		raw_spin_lock(&rq1->__lock);
 		__acquire(rq2->lock);	/* Fake it out ;) */
 	} else {
 		if (rq1 < rq2) {
-			raw_spin_lock(&rq1->lock);
-			raw_spin_lock_nested(&rq2->lock, SINGLE_DEPTH_NESTING);
+			raw_spin_lock(&rq1->__lock);
+			raw_spin_lock_nested(&rq2->__lock, SINGLE_DEPTH_NESTING);
 		} else {
-			raw_spin_lock(&rq2->lock);
-			raw_spin_lock_nested(&rq1->lock, SINGLE_DEPTH_NESTING);
+			raw_spin_lock(&rq2->__lock);
+			raw_spin_lock_nested(&rq1->__lock, SINGLE_DEPTH_NESTING);
 		}
 	}
 }
@@ -1430,9 +1451,9 @@ static inline void double_rq_unlock(stru
 	__releases(rq1->lock)
 	__releases(rq2->lock)
 {
-	raw_spin_unlock(&rq1->lock);
+	raw_spin_unlock(&rq1->__lock);
 	if (rq1 != rq2)
-		raw_spin_unlock(&rq2->lock);
+		raw_spin_unlock(&rq2->__lock);
 	else
 		__release(rq2->lock);
 }
@@ -1451,7 +1472,7 @@ static inline void double_rq_lock(struct
 {
 	BUG_ON(!irqs_disabled());
 	BUG_ON(rq1 != rq2);
-	raw_spin_lock(&rq1->lock);
+	raw_spin_lock(&rq1->__lock);
 	__acquire(rq2->lock);	/* Fake it out ;) */
 }
 
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -788,6 +788,13 @@ config SCHED_DEBUG
 	  that can help debug the scheduler. The runtime overhead of this
 	  option is minimal.
 
+config SCHED_DEBUG_CLOCK
+	bool "Debug rq clock"
+	depends on SCHED_DEBUG
+	default n
+	help
+	  If you say Y here the ftrace output contains debug muck for rq->clock
+
 config SCHEDSTATS
 	bool "Collect scheduler statistics"
 	depends on DEBUG_KERNEL && PROC_FS

Re: [PATCH 1/2] sched: Rework migrate_tasks()

[Kirill Tkhai]

Hi, Mike,

В Чт, 12/06/2014 в 04:05 +0200, Mike Galbraith пишет:
> On Wed, 2014-06-11 at 23:33 +0400, Kirill Tkhai wrote: 
> > В Ср, 11/06/2014 в 17:43 +0400, Kirill Tkhai пишет:
> > > 
> > > 11.06.2014, 17:15, "Srikar Dronamraju" <srikar@linux.vnet.ibm.com>:
> > > >>>  * Kirill Tkhai <ktkhai@parallels.com> [2014-06-11 13:52:10]:
> > > >>>>   Currently migrate_tasks() skips throttled tasks,
> > > >>>>   because they are not pickable by pick_next_task().
> > > >>>  Before migrate_tasks() is called, we do call set_rq_offline(), in
> > > >>>  migration_call().
> > > >>>
> > > >>>  Shouldnt this take care of unthrottling the tasks and making sure that
> > > >>>  they can be picked by pick_next_task().
> > > >>  If we do this separate for every class, we'll have to do this 3 times.
> > > >>  Furthermore, deadline class does not have a list of throttled tasks.
> > > >>  So we'll have to the same as I did: to lock tasklist_lock and to iterate
> > > >>  throw all of the tasks in the system just to found deadline tasks.
> > > >
> > > > I think you misread my comment.
> > > >
> > > > Currently migrate_task() gets called from migration_call() and in the
> > > > migration_call() before migrate_tasks(), set_rq_offline() should put
> > > > tasks back using unthrottle_cfs_rq().
> > > >
> > > > So my question is: Why are these tasks not getting unthrottled
> > > > through we are calling set_rq_offline? To me set_rq_offline is
> > > > calling the actual sched class routines to do the needful.
> > > >
> > > > I can understand about deadline tasks, because we don't have a deadline
> > > > But thats the only tasks that we need to fix.
> > > 
> > > Hm, I tested that on fair class tasks. They used to disappear from
> > > /proc/sched_debug and used to hang. I'll check all once again.
> > > 
> > > I'm agree with you, if set_rq_offline() already presents, we should use it.
> > > 
> > > /me went to clarify why it does not work in my test.
> > 
> > Ok, it looks like the problem is that unthrottled cfs_rq may become throttled
> > again ;)
> 
> Dejavu.  You could try either of the below.

thanks for your suggestion and very sorry for the delay in the reply.

This does not decide my problem. I found it's connected with different
thing. My initial assumption was wrong. If we freeze the clock, we should
keep it freezed for all _cpu_down() execution, and it's not good decidion.

I'll send one more series, which fixes individual class .rq_offline().

Regards,
	Kirill


> On Thu, Apr 03, 2014 at 10:02:18AM +0200, Mike Galbraith wrote:
> > Prevent large wakeup latencies from being accounted to the wrong task.
> > 
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: 	Mike Galbraith <umgwanakikbuti@gmail.com>
> > ---
> >  kernel/sched/core.c |    7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -118,7 +118,12 @@ void update_rq_clock(struct rq *rq)
> >  {
> >  	s64 delta;
> >  
> > -	if (rq->skip_clock_update > 0)
> > +	/*
> > +	 * Set during wakeup to indicate we are on the way to schedule().
> > +	 * Decrement to ensure that a very large latency is not accounted
> > +	 * to the wrong task.
> > +	 */
> > +	if (rq->skip_clock_update-- > 0)
> >  		return;
> >  
> >  	delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
> 
> OK; so as previously mentioned (Oct '13); I've entirely had it with
> skip_clock_update bugs, so I got angry and did the below.
> 
> Its not something I can merge, not least because it uses trace_printk(),
> but it should be usable to 1) demonstate the above actually helps and 2)
> make damn sure we got it right this time :-)
> 
> I've not really stared at the output much yet; but when you select
> function_graph tracer; we get lovely things like:
> 
>   8)               |                                          wake_up_process() {
>   8)               |                                            try_to_wake_up() {
>   8)   0.076 us    |                                              _raw_spin_lock_irqsave();
>   8)   0.092 us    |                                              task_waking_fair();
>   8)   0.106 us    |                                              select_task_rq_fair();
>   8)   0.161 us    |                                              _raw_spin_lock();
>   8)               |                                              ttwu_do_activate.constprop.103() {
>   8)               |                                                activate_task() {
>   8)               |                                                  enqueue_task() {
>   8)               |                                                    update_rq_clock() {
>   8)               |                                                      /* clock update: 420411 */
>   8)   0.084 us    |                                                      sched_avg_update();
>   8)   1.277 us    |                                                    }
>   8)               |                                                    enqueue_task_fair() {
>   8)               |                                                      enqueue_entity() {
>   8)   0.083 us    |                                                        update_curr();
>   8)   0.071 us    |                                                        __compute_runnable_contrib();
>   8)   0.074 us    |                                                        __update_entity_load_avg_contrib();
>   8)   0.121 us    |                                                        update_cfs_rq_blocked_load();
>   8)   0.236 us    |                                                        account_entity_enqueue();
>   8)   0.076 us    |                                                        update_cfs_shares();
>   8)   0.075 us    |                                                        place_entity();
>   8)   0.123 us    |                                                        __enqueue_entity();
>   8)   5.260 us    |                                                      }
>   8)   0.069 us    |                                                      __compute_runnable_contrib();
>   8)   0.073 us    |                                                      hrtick_update();
>   8)   7.146 us    |                                                    }
>   8)   9.583 us    |                                                  }
>   8) + 10.169 us   |                                                }
>   8)               |                                                wq_worker_waking_up() {
>   8)   0.071 us    |                                                  kthread_data();
>   8)   0.682 us    |                                                }
>   8)               |                                                ttwu_do_wakeup() {
>   8)               |                                                  check_preempt_curr() {
>   8)   0.077 us    |                                                    resched_task();
>   8)               |                                                    /* skip_clock_update on cpu: 8 */
>   8)   1.188 us    |                                                  }
>   8)   1.914 us    |                                                }
>   8) + 14.533 us   |                                              }
>   8)   0.071 us    |                                              _raw_spin_unlock();
>   8)   0.082 us    |                                              _raw_spin_unlock_irqrestore();
>   8) + 18.874 us   |                                            }
>   8) + 19.509 us   |                                          }
> 
> ...
> 
>   8)               |                                          wake_up_process() {
>   8)               |                                            try_to_wake_up() {
>   8)   0.101 us    |                                              _raw_spin_lock_irqsave();
>   8)   0.089 us    |                                              task_waking_fair();
>   8)   0.071 us    |                                              select_task_rq_fair();
>   8)   0.070 us    |                                              _raw_spin_lock();
>   8)               |                                              ttwu_do_activate.constprop.103() {
>   8)               |                                                activate_task() {
>   8)               |                                                  enqueue_task() {
>   8)               |                                                    update_rq_clock() {
>   8)               |                                                      /* Invalid clock skip on cpu: 8 */
>   8)               |                                                      /* clock update: 420413 */
>   8)   0.942 us    |                                                    }
>   8)               |                                                    enqueue_task_fair() {
>   8)               |                                                      enqueue_entity() {
>   8)   0.081 us    |                                                        update_curr();
>   8)   0.074 us    |                                                        __compute_runnable_contrib();
>   8)   0.069 us    |                                                        __update_entity_load_avg_contrib();
>   8)   0.091 us    |                                                        update_cfs_rq_blocked_load();
>   8)   0.108 us    |                                                        account_entity_enqueue();
>   8)   0.081 us    |                                                        update_cfs_shares();
>   8)   0.069 us    |                                                        place_entity();
>   8)   0.107 us    |                                                        __enqueue_entity();
>   8)   5.120 us    |                                                      }
>   8)   0.068 us    |                                                      hrtick_update();
>   8)   6.410 us    |                                                    }
>   8)   8.484 us    |                                                  }
>   8)   9.045 us    |                                                }
>   8)               |                                                wq_worker_waking_up() {
>   8)   0.074 us    |                                                  kthread_data();
>   8)   0.669 us    |                                                }
>   8)               |                                                ttwu_do_wakeup() {
>   8)               |                                                  check_preempt_curr() {
>   8)   0.091 us    |                                                    resched_task();
>   8)               |                                                    /* skip_clock_update on cpu: 8 */
>   8)   1.080 us    |                                                  }
>   8)   1.709 us    |                                                }
>   8) + 13.007 us   |                                              }
>   8)   0.071 us    |                                              _raw_spin_unlock();
>   8)   0.090 us    |                                              _raw_spin_unlock_irqrestore();
>   8) + 17.105 us   |                                            }
>   8) + 17.702 us   |                                          }
> 
> ...
> 
>   8)               |  schedule_preempt_disabled() {
>   8)               |    schedule() {
>   8)               |    __schedule() {
>   8)   0.105 us    |      rcu_note_context_switch();
>   8)   0.078 us    |      _raw_spin_lock();
>   8)               |      update_rq_clock() {
>   8)               |        /* Invalid clock skip on cpu: 8 */
>   8)               |        /* clock update: 420415 */
>   8)   0.073 us    |        sched_avg_update();
>   8)   1.630 us    |      }
>   8)   0.080 us    |      pick_next_task_stop();
>   8)   0.112 us    |      pick_next_task_dl();
>   8)   0.088 us    |      pick_next_task_rt();
>   8)               |      pick_next_task_fair() {
>   8)               |        put_prev_task_idle() {
>   8)   0.118 us    |          idle_exit_fair();
>   8)   0.709 us    |        }
>   8)               |        pick_next_entity() {
>   8)   0.071 us    |          clear_buddies();
>   8)   0.721 us    |        }
>   8)               |        set_next_entity() {
>   8)   0.139 us    |          __dequeue_entity();
>   8)   0.732 us    |        }
>   8)   3.804 us    |      }
>  ------------------------------------------
>   8)    <idle>-0    =>   <...>-220   
>  ------------------------------------------
> 
>   8)               |      finish_task_switch() {
>   8)   0.076 us    |        _raw_spin_unlock();
>   8)   0.716 us    |      }
>   8) ! 1876.643 us |    }
>   8) ! 1877.297 us |  } /* schedule */
> 
> Also; did I say how much I hate that function_graph doesn't default to
> latency-format ?
> 
> ---
>  kernel/sched/core.c      |  130 +++++++++++++++++++++++++++++------------------
>  kernel/sched/deadline.c  |    6 +-
>  kernel/sched/debug.c     |    7 +-
>  kernel/sched/fair.c      |   50 ++++++++++--------
>  kernel/sched/idle_task.c |    4 -
>  kernel/sched/proc.c      |    4 -
>  kernel/sched/rt.c        |    4 -
>  kernel/sched/sched.h     |  105 ++++++++++++++++++++++---------------
>  lib/Kconfig.debug        |    7 ++
>  9 files changed, 195 insertions(+), 122 deletions(-)
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -135,11 +135,31 @@ void update_rq_clock(struct rq *rq)
>  {
>  	s64 delta;
>  
> +#ifdef CONFIG_SCHED_DEBUG_CLOCK
> +	if (rq->skip_clock_update > 0 && rq->clock_stamp != rq->clock_seq) {
> +		rq->skip_clock_update = 0;
> +		trace_printk("Invalid clock skip on cpu: %d\n", rq->cpu);
> +		goto do_update;
> +	}
> +#endif
> +
>  	if (rq->skip_clock_update > 0)
>  		return;
>  
> -	delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
> -	rq->clock += delta;
> +#ifdef CONFIG_SCHED_DEBUG_CLOCK
> +	if (!(rq->clock_stamp & 1))
> +		trace_printk("clock update outside of rq->lock\n");
> +
> +	if (rq->clock_stamp == rq->clock_seq)
> +		trace_printk("superfluous clock update\n");
> +
> +do_update:
> +	trace_printk("clock update: %u\n", rq->clock_seq);
> +	rq->clock_stamp = rq->clock_seq;
> +#endif
> +
> +	delta = sched_clock_cpu(cpu_of(rq)) - rq->__clock;
> +	rq->__clock += delta;
>  	update_rq_clock_task(rq, delta);
>  }
>  
> @@ -325,10 +345,10 @@ static inline struct rq *__task_rq_lock(
>  
>  	for (;;) {
>  		rq = task_rq(p);
> -		raw_spin_lock(&rq->lock);
> +		rq_lock(rq);
>  		if (likely(rq == task_rq(p)))
>  			return rq;
> -		raw_spin_unlock(&rq->lock);
> +		rq_unlock(rq);
>  	}
>  }
>  
> @@ -344,10 +364,10 @@ static struct rq *task_rq_lock(struct ta
>  	for (;;) {
>  		raw_spin_lock_irqsave(&p->pi_lock, *flags);
>  		rq = task_rq(p);
> -		raw_spin_lock(&rq->lock);
> +		rq_lock(rq);
>  		if (likely(rq == task_rq(p)))
>  			return rq;
> -		raw_spin_unlock(&rq->lock);
> +		rq_unlock(rq);
>  		raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
>  	}
>  }
> @@ -355,7 +375,7 @@ static struct rq *task_rq_lock(struct ta
>  static void __task_rq_unlock(struct rq *rq)
>  	__releases(rq->lock)
>  {
> -	raw_spin_unlock(&rq->lock);
> +	rq_unlock(rq);
>  }
>  
>  static inline void
> @@ -363,7 +383,7 @@ task_rq_unlock(struct rq *rq, struct tas
>  	__releases(rq->lock)
>  	__releases(p->pi_lock)
>  {
> -	raw_spin_unlock(&rq->lock);
> +	rq_unlock(rq);
>  	raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
>  }
>  
> @@ -377,7 +397,7 @@ static struct rq *this_rq_lock(void)
>  
>  	local_irq_disable();
>  	rq = this_rq();
> -	raw_spin_lock(&rq->lock);
> +	rq_lock(rq);
>  
>  	return rq;
>  }
> @@ -403,10 +423,10 @@ static enum hrtimer_restart hrtick(struc
>  
>  	WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
>  
> -	raw_spin_lock(&rq->lock);
> +	rq_lock(rq);
>  	update_rq_clock(rq);
>  	rq->curr->sched_class->task_tick(rq, rq->curr, 1);
> -	raw_spin_unlock(&rq->lock);
> +	rq_unlock(rq);
>  
>  	return HRTIMER_NORESTART;
>  }
> @@ -428,10 +448,10 @@ static void __hrtick_start(void *arg)
>  {
>  	struct rq *rq = arg;
>  
> -	raw_spin_lock(&rq->lock);
> +	rq_lock(rq);
>  	__hrtick_restart(rq);
>  	rq->hrtick_csd_pending = 0;
> -	raw_spin_unlock(&rq->lock);
> +	rq_unlock(rq);
>  }
>  
>  /*
> @@ -565,7 +585,7 @@ void resched_task(struct task_struct *p)
>  {
>  	int cpu;
>  
> -	lockdep_assert_held(&task_rq(p)->lock);
> +	lockdep_assert_held(&task_rq(p)->__lock);
>  
>  	if (test_tsk_need_resched(p))
>  		return;
> @@ -587,10 +607,10 @@ void resched_cpu(int cpu)
>  	struct rq *rq = cpu_rq(cpu);
>  	unsigned long flags;
>  
> -	if (!raw_spin_trylock_irqsave(&rq->lock, flags))
> +	if (!raw_spin_trylock_irqsave(&rq->__lock, flags))
>  		return;
>  	resched_task(cpu_curr(cpu));
> -	raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	raw_spin_unlock_irqrestore(&rq->__lock, flags);
>  }
>  
>  #ifdef CONFIG_SMP
> @@ -893,7 +913,7 @@ static void update_rq_clock_task(struct
>  	}
>  #endif
>  
> -	rq->clock_task += delta;
> +	rq->__clock_task += delta;
>  
>  #if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
>  	if ((irq_delta + steal) && sched_feat(NONTASK_POWER))
> @@ -1023,8 +1043,10 @@ void check_preempt_curr(struct rq *rq, s
>  	 * A queue event has occurred, and we're going to schedule.  In
>  	 * this case, we can save a useless back to back clock update.
>  	 */
> -	if (rq->curr->on_rq && test_tsk_need_resched(rq->curr))
> +	if (rq->curr->on_rq && test_tsk_need_resched(rq->curr)) {
> +		trace_printk("skip_clock_update on cpu: %d\n", rq->cpu);
>  		rq->skip_clock_update = 1;
> +	}
>  }
>  
>  #ifdef CONFIG_SMP
> @@ -1535,7 +1557,7 @@ static void sched_ttwu_pending(void)
>  	struct llist_node *llist = llist_del_all(&rq->wake_list);
>  	struct task_struct *p;
>  
> -	raw_spin_lock(&rq->lock);
> +	rq_lock(rq);
>  
>  	while (llist) {
>  		p = llist_entry(llist, struct task_struct, wake_entry);
> @@ -1543,7 +1565,7 @@ static void sched_ttwu_pending(void)
>  		ttwu_do_activate(rq, p, 0);
>  	}
>  
> -	raw_spin_unlock(&rq->lock);
> +	rq_unlock(rq);
>  }
>  
>  void scheduler_ipi(void)
> @@ -1611,9 +1633,9 @@ static void ttwu_queue(struct task_struc
>  	}
>  #endif
>  
> -	raw_spin_lock(&rq->lock);
> +	rq_lock(rq);
>  	ttwu_do_activate(rq, p, 0);
> -	raw_spin_unlock(&rq->lock);
> +	rq_unlock(rq);
>  }
>  
>  /**
> @@ -1704,12 +1726,12 @@ static void try_to_wake_up_local(struct
>  	    WARN_ON_ONCE(p == current))
>  		return;
>  
> -	lockdep_assert_held(&rq->lock);
> +	lockdep_assert_held(&rq->__lock);
>  
>  	if (!raw_spin_trylock(&p->pi_lock)) {
> -		raw_spin_unlock(&rq->lock);
> +		raw_spin_unlock(&rq->__lock);
>  		raw_spin_lock(&p->pi_lock);
> -		raw_spin_lock(&rq->lock);
> +		raw_spin_lock(&rq->__lock);
>  	}
>  
>  	if (!(p->state & TASK_NORMAL))
> @@ -2226,10 +2248,12 @@ static inline void post_schedule(struct
>  	if (rq->post_schedule) {
>  		unsigned long flags;
>  
> -		raw_spin_lock_irqsave(&rq->lock, flags);
> +		local_irq_save(flags);
> +		rq_lock(rq);
>  		if (rq->curr->sched_class->post_schedule)
>  			rq->curr->sched_class->post_schedule(rq);
> -		raw_spin_unlock_irqrestore(&rq->lock, flags);
> +		rq_unlock(rq);
> +		local_irq_restore(flags);
>  
>  		rq->post_schedule = 0;
>  	}
> @@ -2479,11 +2503,11 @@ void scheduler_tick(void)
>  
>  	sched_clock_tick();
>  
> -	raw_spin_lock(&rq->lock);
> +	rq_lock(rq);
>  	update_rq_clock(rq);
>  	curr->sched_class->task_tick(rq, curr, 0);
>  	update_cpu_load_active(rq);
> -	raw_spin_unlock(&rq->lock);
> +	rq_unlock(rq);
>  
>  	perf_event_task_tick();
>  
> @@ -2732,7 +2756,8 @@ static void __sched __schedule(void)
>  	 * done by the caller to avoid the race with signal_wake_up().
>  	 */
>  	smp_mb__before_spinlock();
> -	raw_spin_lock_irq(&rq->lock);
> +	local_irq_disable();
> +	rq_lock(rq);
>  
>  	switch_count = &prev->nivcsw;
>  	if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
> @@ -2780,8 +2805,10 @@ static void __sched __schedule(void)
>  		 */
>  		cpu = smp_processor_id();
>  		rq = cpu_rq(cpu);
> -	} else
> -		raw_spin_unlock_irq(&rq->lock);
> +	} else {
> +		rq_unlock(rq);
> +		local_irq_enable();
> +	}
>  
>  	post_schedule(rq);
>  
> @@ -4106,9 +4133,8 @@ SYSCALL_DEFINE0(sched_yield)
>  	 * Since we are going to call schedule() anyway, there's
>  	 * no need to preempt or enable interrupts:
>  	 */
> -	__release(rq->lock);
> -	spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
> -	do_raw_spin_unlock(&rq->lock);
> +	preempt_disable();
> +	rq_unlock(rq);
>  	sched_preempt_enable_no_resched();
>  
>  	schedule();
> @@ -4510,7 +4536,8 @@ void init_idle(struct task_struct *idle,
>  	struct rq *rq = cpu_rq(cpu);
>  	unsigned long flags;
>  
> -	raw_spin_lock_irqsave(&rq->lock, flags);
> +	local_irq_save(flags);
> +	rq_lock(rq);
>  
>  	__sched_fork(0, idle);
>  	idle->state = TASK_RUNNING;
> @@ -4536,7 +4563,8 @@ void init_idle(struct task_struct *idle,
>  #if defined(CONFIG_SMP)
>  	idle->on_cpu = 1;
>  #endif
> -	raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	rq_unlock(rq);
> +	local_irq_restore(flags);
>  
>  	/* Set the preempt count _outside_ the spinlocks! */
>  	init_idle_preempt_count(idle, cpu);
> @@ -4835,11 +4863,11 @@ static void migrate_tasks(unsigned int d
>  
>  		/* Find suitable destination for @next, with force if needed. */
>  		dest_cpu = select_fallback_rq(dead_cpu, next);
> -		raw_spin_unlock(&rq->lock);
> +		rq_unlock(rq);
>  
>  		__migrate_task(next, dead_cpu, dest_cpu);
>  
> -		raw_spin_lock(&rq->lock);
> +		rq_lock(rq);
>  	}
>  
>  	rq->stop = stop;
> @@ -5100,27 +5128,31 @@ migration_call(struct notifier_block *nf
>  
>  	case CPU_ONLINE:
>  		/* Update our root-domain */
> -		raw_spin_lock_irqsave(&rq->lock, flags);
> +		local_irq_save(flags);
> +		rq_lock(rq);
>  		if (rq->rd) {
>  			BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
>  
>  			set_rq_online(rq);
>  		}
> -		raw_spin_unlock_irqrestore(&rq->lock, flags);
> +		rq_unlock(rq);
> +		local_irq_restore(flags);
>  		break;
>  
>  #ifdef CONFIG_HOTPLUG_CPU
>  	case CPU_DYING:
>  		sched_ttwu_pending();
>  		/* Update our root-domain */
> -		raw_spin_lock_irqsave(&rq->lock, flags);
> +		local_irq_save(flags);
> +		rq_lock(rq);
>  		if (rq->rd) {
>  			BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
>  			set_rq_offline(rq);
>  		}
>  		migrate_tasks(cpu);
>  		BUG_ON(rq->nr_running != 1); /* the migration thread */
> -		raw_spin_unlock_irqrestore(&rq->lock, flags);
> +		rq_unlock(rq);
> +		local_irq_restore(flags);
>  		break;
>  
>  	case CPU_DEAD:
> @@ -5427,7 +5459,8 @@ static void rq_attach_root(struct rq *rq
>  	struct root_domain *old_rd = NULL;
>  	unsigned long flags;
>  
> -	raw_spin_lock_irqsave(&rq->lock, flags);
> +	local_irq_save(flags);
> +	rq_lock(rq);
>  
>  	if (rq->rd) {
>  		old_rd = rq->rd;
> @@ -5453,7 +5486,8 @@ static void rq_attach_root(struct rq *rq
>  	if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
>  		set_rq_online(rq);
>  
> -	raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	rq_unlock(rq);
> +	local_irq_restore(flags);
>  
>  	if (old_rd)
>  		call_rcu_sched(&old_rd->rcu, free_rootdomain);
> @@ -6931,7 +6965,7 @@ void __init sched_init(void)
>  		struct rq *rq;
>  
>  		rq = cpu_rq(i);
> -		raw_spin_lock_init(&rq->lock);
> +		raw_spin_lock_init(&rq->__lock);
>  		rq->nr_running = 0;
>  		rq->calc_load_active = 0;
>  		rq->calc_load_update = jiffies + LOAD_FREQ;
> @@ -7842,13 +7876,13 @@ static int tg_set_cfs_bandwidth(struct t
>  		struct cfs_rq *cfs_rq = tg->cfs_rq[i];
>  		struct rq *rq = cfs_rq->rq;
>  
> -		raw_spin_lock_irq(&rq->lock);
> +		raw_spin_lock_irq(&rq->__lock);
>  		cfs_rq->runtime_enabled = runtime_enabled;
>  		cfs_rq->runtime_remaining = 0;
>  
>  		if (cfs_rq->throttled)
>  			unthrottle_cfs_rq(cfs_rq);
> -		raw_spin_unlock_irq(&rq->lock);
> +		raw_spin_unlock_irq(&rq->__lock);
>  	}
>  	if (runtime_was_enabled && !runtime_enabled)
>  		cfs_bandwidth_usage_dec();
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -511,11 +511,11 @@ static enum hrtimer_restart dl_task_time
>  	struct rq *rq;
>  again:
>  	rq = task_rq(p);
> -	raw_spin_lock(&rq->lock);
> +	rq_lock(rq);
>  
>  	if (rq != task_rq(p)) {
>  		/* Task was moved, retrying. */
> -		raw_spin_unlock(&rq->lock);
> +		rq_unlock(rq);
>  		goto again;
>  	}
>  
> @@ -548,7 +548,7 @@ static enum hrtimer_restart dl_task_time
>  #endif
>  	}
>  unlock:
> -	raw_spin_unlock(&rq->lock);
> +	rq_unlock(rq);
>  
>  	return HRTIMER_NORESTART;
>  }
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -187,7 +187,7 @@ void print_cfs_rq(struct seq_file *m, in
>  	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "exec_clock",
>  			SPLIT_NS(cfs_rq->exec_clock));
>  
> -	raw_spin_lock_irqsave(&rq->lock, flags);
> +	raw_spin_lock_irqsave(&rq->__lock, flags);
>  	if (cfs_rq->rb_leftmost)
>  		MIN_vruntime = (__pick_first_entity(cfs_rq))->vruntime;
>  	last = __pick_last_entity(cfs_rq);
> @@ -195,7 +195,7 @@ void print_cfs_rq(struct seq_file *m, in
>  		max_vruntime = last->vruntime;
>  	min_vruntime = cfs_rq->min_vruntime;
>  	rq0_min_vruntime = cpu_rq(0)->cfs.min_vruntime;
> -	raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	raw_spin_unlock_irqrestore(&rq->__lock, flags);
>  	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "MIN_vruntime",
>  			SPLIT_NS(MIN_vruntime));
>  	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "min_vruntime",
> @@ -301,7 +301,8 @@ do {									\
>  	P(nr_uninterruptible);
>  	PN(next_balance);
>  	SEQ_printf(m, "  .%-30s: %ld\n", "curr->pid", (long)(task_pid_nr(rq->curr)));
> -	PN(clock);
> +	PN(__clock);
> +	PN(__clock_task);
>  	P(cpu_load[0]);
>  	P(cpu_load[1]);
>  	P(cpu_load[2]);
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3421,7 +3421,7 @@ static u64 distribute_cfs_runtime(struct
>  				throttled_list) {
>  		struct rq *rq = rq_of(cfs_rq);
>  
> -		raw_spin_lock(&rq->lock);
> +		raw_spin_lock(&rq->__lock);
>  		if (!cfs_rq_throttled(cfs_rq))
>  			goto next;
>  
> @@ -3438,7 +3438,7 @@ static u64 distribute_cfs_runtime(struct
>  			unthrottle_cfs_rq(cfs_rq);
>  
>  next:
> -		raw_spin_unlock(&rq->lock);
> +		raw_spin_unlock(&rq->__lock);
>  
>  		if (!remaining)
>  			break;
> @@ -4901,7 +4901,8 @@ static void yield_task_fair(struct rq *r
>  		 * so we don't do microscopic update in schedule()
>  		 * and double the fastpath cost.
>  		 */
> -		 rq->skip_clock_update = 1;
> +		trace_printk("skip_clock_update on cpu: %d\n", rq->cpu);
> +		rq->skip_clock_update = 1;
>  	}
>  
>  	set_skip_buddy(se);
> @@ -5446,7 +5447,8 @@ static void update_blocked_averages(int
>  	struct cfs_rq *cfs_rq;
>  	unsigned long flags;
>  
> -	raw_spin_lock_irqsave(&rq->lock, flags);
> +	local_irq_save(flags);
> +	rq_lock(rq);
>  	update_rq_clock(rq);
>  	/*
>  	 * Iterates the task_group tree in a bottom up fashion, see
> @@ -5461,7 +5463,8 @@ static void update_blocked_averages(int
>  		__update_blocked_averages_cpu(cfs_rq->tg, rq->cpu);
>  	}
>  
> -	raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	rq_unlock(rq);
> +	local_irq_restore(flags);
>  }
>  
>  /*
> @@ -6641,7 +6644,7 @@ static int load_balance(int this_cpu, st
>  			sd->nr_balance_failed++;
>  
>  		if (need_active_balance(&env)) {
> -			raw_spin_lock_irqsave(&busiest->lock, flags);
> +			raw_spin_lock_irqsave(&busiest->__lock, flags);
>  
>  			/* don't kick the active_load_balance_cpu_stop,
>  			 * if the curr task on busiest cpu can't be
> @@ -6649,7 +6652,7 @@ static int load_balance(int this_cpu, st
>  			 */
>  			if (!cpumask_test_cpu(this_cpu,
>  					tsk_cpus_allowed(busiest->curr))) {
> -				raw_spin_unlock_irqrestore(&busiest->lock,
> +				raw_spin_unlock_irqrestore(&busiest->__lock,
>  							    flags);
>  				env.flags |= LBF_ALL_PINNED;
>  				goto out_one_pinned;
> @@ -6665,7 +6668,7 @@ static int load_balance(int this_cpu, st
>  				busiest->push_cpu = this_cpu;
>  				active_balance = 1;
>  			}
> -			raw_spin_unlock_irqrestore(&busiest->lock, flags);
> +			raw_spin_unlock_irqrestore(&busiest->__lock, flags);
>  
>  			if (active_balance) {
>  				stop_one_cpu_nowait(cpu_of(busiest),
> @@ -6775,7 +6778,7 @@ static int idle_balance(struct rq *this_
>  	/*
>  	 * Drop the rq->lock, but keep IRQ/preempt disabled.
>  	 */
> -	raw_spin_unlock(&this_rq->lock);
> +	raw_spin_unlock(&this_rq->__lock);
>  
>  	update_blocked_averages(this_cpu);
>  	rcu_read_lock();
> @@ -6816,7 +6819,7 @@ static int idle_balance(struct rq *this_
>  	}
>  	rcu_read_unlock();
>  
> -	raw_spin_lock(&this_rq->lock);
> +	raw_spin_lock(&this_rq->__lock);
>  
>  	if (curr_cost > this_rq->max_idle_balance_cost)
>  		this_rq->max_idle_balance_cost = curr_cost;
> @@ -6860,7 +6863,7 @@ static int active_load_balance_cpu_stop(
>  	struct rq *target_rq = cpu_rq(target_cpu);
>  	struct sched_domain *sd;
>  
> -	raw_spin_lock_irq(&busiest_rq->lock);
> +	raw_spin_lock_irq(&busiest_rq->__lock);
>  
>  	/* make sure the requested cpu hasn't gone down in the meantime */
>  	if (unlikely(busiest_cpu != smp_processor_id() ||
> @@ -6910,7 +6913,7 @@ static int active_load_balance_cpu_stop(
>  	double_unlock_balance(busiest_rq, target_rq);
>  out_unlock:
>  	busiest_rq->active_balance = 0;
> -	raw_spin_unlock_irq(&busiest_rq->lock);
> +	raw_spin_unlock_irq(&busiest_rq->__lock);
>  	return 0;
>  }
>  
> @@ -7192,10 +7195,12 @@ static void nohz_idle_balance(struct rq
>  
>  		rq = cpu_rq(balance_cpu);
>  
> -		raw_spin_lock_irq(&rq->lock);
> +		local_irq_disable();
> +		rq_lock(rq);
>  		update_rq_clock(rq);
>  		update_idle_cpu_load(rq);
> -		raw_spin_unlock_irq(&rq->lock);
> +		rq_unlock(rq);
> +		local_irq_enable();
>  
>  		rebalance_domains(rq, CPU_IDLE);
>  
> @@ -7359,7 +7364,8 @@ static void task_fork_fair(struct task_s
>  	struct rq *rq = this_rq();
>  	unsigned long flags;
>  
> -	raw_spin_lock_irqsave(&rq->lock, flags);
> +	local_irq_save(flags);
> +	rq_lock(rq);
>  
>  	update_rq_clock(rq);
>  
> @@ -7393,7 +7399,8 @@ static void task_fork_fair(struct task_s
>  
>  	se->vruntime -= cfs_rq->min_vruntime;
>  
> -	raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	rq_unlock(rq);
> +	local_irq_restore(flags);
>  }
>  
>  /*
> @@ -7634,9 +7641,9 @@ void unregister_fair_sched_group(struct
>  	if (!tg->cfs_rq[cpu]->on_list)
>  		return;
>  
> -	raw_spin_lock_irqsave(&rq->lock, flags);
> +	raw_spin_lock_irqsave(&rq->__lock, flags);
>  	list_del_leaf_cfs_rq(tg->cfs_rq[cpu]);
> -	raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	raw_spin_unlock_irqrestore(&rq->__lock, flags);
>  }
>  
>  void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
> @@ -7696,13 +7703,16 @@ int sched_group_set_shares(struct task_g
>  
>  		se = tg->se[i];
>  		/* Propagate contribution to hierarchy */
> -		raw_spin_lock_irqsave(&rq->lock, flags);
> +		local_irq_save(flags);
> +		rq_lock(rq);
>  
>  		/* Possible calls to update_curr() need rq clock */
>  		update_rq_clock(rq);
>  		for_each_sched_entity(se)
>  			update_cfs_shares(group_cfs_rq(se));
> -		raw_spin_unlock_irqrestore(&rq->lock, flags);
> +
> +		rq_unlock(rq);
> +		local_irq_restore(flags);
>  	}
>  
>  done:
> --- a/kernel/sched/idle_task.c
> +++ b/kernel/sched/idle_task.c
> @@ -39,10 +39,10 @@ pick_next_task_idle(struct rq *rq, struc
>  static void
>  dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
>  {
> -	raw_spin_unlock_irq(&rq->lock);
> +	raw_spin_unlock_irq(&rq->__lock);
>  	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
>  	dump_stack();
> -	raw_spin_lock_irq(&rq->lock);
> +	raw_spin_lock_irq(&rq->__lock);
>  }
>  
>  static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
> --- a/kernel/sched/proc.c
> +++ b/kernel/sched/proc.c
> @@ -561,7 +561,7 @@ void update_cpu_load_nohz(void)
>  	if (curr_jiffies == this_rq->last_load_update_tick)
>  		return;
>  
> -	raw_spin_lock(&this_rq->lock);
> +	raw_spin_lock(&this_rq->__lock);
>  	pending_updates = curr_jiffies - this_rq->last_load_update_tick;
>  	if (pending_updates) {
>  		this_rq->last_load_update_tick = curr_jiffies;
> @@ -571,7 +571,7 @@ void update_cpu_load_nohz(void)
>  		 */
>  		__update_cpu_load(this_rq, 0, pending_updates);
>  	}
> -	raw_spin_unlock(&this_rq->lock);
> +	raw_spin_unlock(&this_rq->__lock);
>  }
>  #endif /* CONFIG_NO_HZ */
>  
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -813,7 +813,7 @@ static int do_sched_rt_period_timer(stru
>  		struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);
>  		struct rq *rq = rq_of_rt_rq(rt_rq);
>  
> -		raw_spin_lock(&rq->lock);
> +		rq_lock(rq);
>  		if (rt_rq->rt_time) {
>  			u64 runtime;
>  
> @@ -846,7 +846,7 @@ static int do_sched_rt_period_timer(stru
>  
>  		if (enqueue)
>  			sched_rt_rq_enqueue(rt_rq);
> -		raw_spin_unlock(&rq->lock);
> +		rq_unlock(rq);
>  	}
>  
>  	if (!throttled && (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF))
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -507,7 +507,7 @@ extern struct root_domain def_root_domai
>   */
>  struct rq {
>  	/* runqueue lock: */
> -	raw_spinlock_t lock;
> +	raw_spinlock_t __lock;
>  
>  	/*
>  	 * nr_running and cpu_load should be in the same cacheline because
> @@ -528,7 +528,6 @@ struct rq {
>  #ifdef CONFIG_NO_HZ_FULL
>  	unsigned long last_sched_tick;
>  #endif
> -	int skip_clock_update;
>  
>  	/* capture load from *all* tasks on this cpu: */
>  	struct load_weight load;
> @@ -558,8 +557,11 @@ struct rq {
>  	unsigned long next_balance;
>  	struct mm_struct *prev_mm;
>  
> -	u64 clock;
> -	u64 clock_task;
> +	unsigned int clock_seq;
> +	unsigned int clock_stamp;
> +	int skip_clock_update;
> +	u64 __clock;
> +	u64 __clock_task;
>  
>  	atomic_t nr_iowait;
>  
> @@ -635,6 +637,24 @@ struct rq {
>  #endif
>  };
>  
> +static inline void rq_lock(struct rq *rq)
> +{
> +	raw_spin_lock(&rq->__lock);
> +#ifdef CONFIG_SCHED_DEBUG_CLOCK
> +	rq->clock_seq++;
> +	barrier();
> +#endif
> +}
> +
> +static inline void rq_unlock(struct rq *rq)
> +{
> +#ifdef CONFIG_SCHED_DEBUG_CLOCK
> +	barrier();
> +	rq->clock_seq++;
> +#endif
> +	raw_spin_unlock(&rq->__lock);
> +}
> +
>  static inline int cpu_of(struct rq *rq)
>  {
>  #ifdef CONFIG_SMP
> @@ -654,12 +674,26 @@ DECLARE_PER_CPU(struct rq, runqueues);
>  
>  static inline u64 rq_clock(struct rq *rq)
>  {
> -	return rq->clock;
> +#ifdef CONFIG_SCHED_DEBUG_CLOCK
> +	if (rq->clock_stamp != rq->clock_seq) {
> +		trace_printk("reading invalid rq->clock: %u != %u\n",
> +				rq->clock_stamp, rq->clock_seq);
> +	}
> +#endif
> +
> +	return rq->__clock;
>  }
>  
>  static inline u64 rq_clock_task(struct rq *rq)
>  {
> -	return rq->clock_task;
> +#ifdef CONFIG_SCHED_DEBUG_CLOCK
> +	if (rq->clock_stamp != rq->clock_seq) {
> +		trace_printk("reading invalid rq->clock_task: %u != %u\n",
> +				rq->clock_stamp, rq->clock_seq);
> +	}
> +#endif
> +
> +	return rq->__clock_task;
>  }
>  
>  #ifdef CONFIG_NUMA_BALANCING
> @@ -980,16 +1014,17 @@ static inline void finish_lock_switch(st
>  #endif
>  #ifdef CONFIG_DEBUG_SPINLOCK
>  	/* this is a valid case when another task releases the spinlock */
> -	rq->lock.owner = current;
> +	rq->__lock.owner = current;
>  #endif
>  	/*
>  	 * If we are tracking spinlock dependencies then we have to
>  	 * fix up the runqueue lock - which gets 'carried over' from
>  	 * prev into current:
>  	 */
> -	spin_acquire(&rq->lock.dep_map, 0, 0, _THIS_IP_);
> +	spin_acquire(&rq->__lock.dep_map, 0, 0, _THIS_IP_);
>  
> -	raw_spin_unlock_irq(&rq->lock);
> +	rq_unlock(rq);
> +	local_irq_enable();
>  }
>  
>  #else /* __ARCH_WANT_UNLOCKED_CTXSW */
> @@ -1003,7 +1038,7 @@ static inline void prepare_lock_switch(s
>  	 */
>  	next->on_cpu = 1;
>  #endif
> -	raw_spin_unlock(&rq->lock);
> +	rq_unlock(rq);
>  }
>  
>  static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
> @@ -1305,12 +1340,12 @@ static inline void double_rq_lock(struct
>   * reduces latency compared to the unfair variant below.  However, it
>   * also adds more overhead and therefore may reduce throughput.
>   */
> -static inline int _double_lock_balance(struct rq *this_rq, struct rq *busiest)
> +static inline int double_lock_balance(struct rq *this_rq, struct rq *busiest)
>  	__releases(this_rq->lock)
>  	__acquires(busiest->lock)
>  	__acquires(this_rq->lock)
>  {
> -	raw_spin_unlock(&this_rq->lock);
> +	raw_spin_unlock(&this_rq->__lock);
>  	double_rq_lock(this_rq, busiest);
>  
>  	return 1;
> @@ -1324,22 +1359,22 @@ static inline int _double_lock_balance(s
>   * grant the double lock to lower cpus over higher ids under contention,
>   * regardless of entry order into the function.
>   */
> -static inline int _double_lock_balance(struct rq *this_rq, struct rq *busiest)
> +static inline int double_lock_balance(struct rq *this_rq, struct rq *busiest)
>  	__releases(this_rq->lock)
>  	__acquires(busiest->lock)
>  	__acquires(this_rq->lock)
>  {
>  	int ret = 0;
>  
> -	if (unlikely(!raw_spin_trylock(&busiest->lock))) {
> +	if (unlikely(!raw_spin_trylock(&busiest->__lock))) {
>  		if (busiest < this_rq) {
> -			raw_spin_unlock(&this_rq->lock);
> -			raw_spin_lock(&busiest->lock);
> -			raw_spin_lock_nested(&this_rq->lock,
> +			raw_spin_unlock(&this_rq->__lock);
> +			raw_spin_lock(&busiest->__lock);
> +			raw_spin_lock_nested(&this_rq->__lock,
>  					      SINGLE_DEPTH_NESTING);
>  			ret = 1;
>  		} else
> -			raw_spin_lock_nested(&busiest->lock,
> +			raw_spin_lock_nested(&busiest->__lock,
>  					      SINGLE_DEPTH_NESTING);
>  	}
>  	return ret;
> @@ -1347,25 +1382,11 @@ static inline int _double_lock_balance(s
>  
>  #endif /* CONFIG_PREEMPT */
>  
> -/*
> - * double_lock_balance - lock the busiest runqueue, this_rq is locked already.
> - */
> -static inline int double_lock_balance(struct rq *this_rq, struct rq *busiest)
> -{
> -	if (unlikely(!irqs_disabled())) {
> -		/* printk() doesn't work good under rq->lock */
> -		raw_spin_unlock(&this_rq->lock);
> -		BUG_ON(1);
> -	}
> -
> -	return _double_lock_balance(this_rq, busiest);
> -}
> -
>  static inline void double_unlock_balance(struct rq *this_rq, struct rq *busiest)
>  	__releases(busiest->lock)
>  {
> -	raw_spin_unlock(&busiest->lock);
> -	lock_set_subclass(&this_rq->lock.dep_map, 0, _RET_IP_);
> +	raw_spin_unlock(&busiest->__lock);
> +	lock_set_subclass(&this_rq->__lock.dep_map, 0, _RET_IP_);
>  }
>  
>  static inline void double_lock(spinlock_t *l1, spinlock_t *l2)
> @@ -1407,15 +1428,15 @@ static inline void double_rq_lock(struct
>  {
>  	BUG_ON(!irqs_disabled());
>  	if (rq1 == rq2) {
> -		raw_spin_lock(&rq1->lock);
> +		raw_spin_lock(&rq1->__lock);
>  		__acquire(rq2->lock);	/* Fake it out ;) */
>  	} else {
>  		if (rq1 < rq2) {
> -			raw_spin_lock(&rq1->lock);
> -			raw_spin_lock_nested(&rq2->lock, SINGLE_DEPTH_NESTING);
> +			raw_spin_lock(&rq1->__lock);
> +			raw_spin_lock_nested(&rq2->__lock, SINGLE_DEPTH_NESTING);
>  		} else {
> -			raw_spin_lock(&rq2->lock);
> -			raw_spin_lock_nested(&rq1->lock, SINGLE_DEPTH_NESTING);
> +			raw_spin_lock(&rq2->__lock);
> +			raw_spin_lock_nested(&rq1->__lock, SINGLE_DEPTH_NESTING);
>  		}
>  	}
>  }
> @@ -1430,9 +1451,9 @@ static inline void double_rq_unlock(stru
>  	__releases(rq1->lock)
>  	__releases(rq2->lock)
>  {
> -	raw_spin_unlock(&rq1->lock);
> +	raw_spin_unlock(&rq1->__lock);
>  	if (rq1 != rq2)
> -		raw_spin_unlock(&rq2->lock);
> +		raw_spin_unlock(&rq2->__lock);
>  	else
>  		__release(rq2->lock);
>  }
> @@ -1451,7 +1472,7 @@ static inline void double_rq_lock(struct
>  {
>  	BUG_ON(!irqs_disabled());
>  	BUG_ON(rq1 != rq2);
> -	raw_spin_lock(&rq1->lock);
> +	raw_spin_lock(&rq1->__lock);
>  	__acquire(rq2->lock);	/* Fake it out ;) */
>  }
>  
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -788,6 +788,13 @@ config SCHED_DEBUG
>  	  that can help debug the scheduler. The runtime overhead of this
>  	  option is minimal.
>  
> +config SCHED_DEBUG_CLOCK
> +	bool "Debug rq clock"
> +	depends on SCHED_DEBUG
> +	default n
> +	help
> +	  If you say Y here the ftrace output contains debug muck for rq->clock
> +
>  config SCHEDSTATS
>  	bool "Collect scheduler statistics"
>  	depends on DEBUG_KERNEL && PROC_FS
> 
> 

[PATCH 2/2] sched: Rework check_for_tasks()

[Kirill Tkhai]

1)Iterate throw all of threads in the system.
  Check for all threads, not only for group leaders.

2)Check for p->on_rq instead of p->state and cputime.
  Preempted task in !TASK_RUNNING state  OR just
  created task may be queued, that we want to be
  reported too.

3)Use read_lock() instead of write_lock().
  This function does not change any structures, and
  read_lock() is enough.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@kernel.org>
---
 kernel/cpu.c |   33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index acf791c..c72ba84 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -273,21 +273,28 @@ void clear_tasks_mm_cpumask(int cpu)
 	rcu_read_unlock();
 }
 
-static inline void check_for_tasks(int cpu)
+static inline void check_for_tasks(int dead_cpu)
 {
-	struct task_struct *p;
-	cputime_t utime, stime;
+	struct task_struct *g, *p;
 
-	write_lock_irq(&tasklist_lock);
-	for_each_process(p) {
-		task_cputime(p, &utime, &stime);
-		if (task_cpu(p) == cpu && p->state == TASK_RUNNING &&
-		    (utime || stime))
-			pr_warn("Task %s (pid = %d) is on cpu %d (state = %ld, flags = %x)\n",
-				p->comm, task_pid_nr(p), cpu,
-				p->state, p->flags);
-	}
-	write_unlock_irq(&tasklist_lock);
+	read_lock_irq(&tasklist_lock);
+	do_each_thread(g, p) {
+		if (!p->on_rq)
+			continue;
+		/*
+		 * We do the check with unlocked task_rq(p)->lock.
+		 * Order the reading to do not warn about a task,
+		 * which was running on this cpu in the past, and
+		 * it's just been woken on another cpu.
+		 */
+		rmb();
+		if (task_cpu(p) != dead_cpu)
+			continue;
+
+		pr_warn("Task %s (pid=%d) is on cpu %d (state=%ld, flags=%x)\n",
+			p->comm, task_pid_nr(p), dead_cpu, p->state, p->flags);
+	} while_each_thread(g, p);
+	read_unlock_irq(&tasklist_lock);
 }
 
 struct take_cpu_down_param {