Re: [PATCH] sched: update_rq_clock() must skip ONE update

From: Peter Zijlstra
Date: Tue Apr 08 2014 - 11:53:37 EST

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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@xxxxxxxxxxxxxxx>
> Signed-off-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
> ---
> 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 | 5 +-
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(+), 121 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9cae286824bb..0e5c3dc6ed29 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -118,11 +118,31 @@ 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);
}

@@ -308,10 +328,10 @@ static inline struct rq *__task_rq_lock(struct task_struct *p)

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);
}
}

@@ -327,10 +347,10 @@ static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
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);
}
}
@@ -338,7 +358,7 @@ static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
static void __task_rq_unlock(struct rq *rq)
__releases(rq->lock)
{
- raw_spin_unlock(&rq->lock);
+ rq_unlock(rq);
}

static inline void
@@ -346,7 +366,7 @@ task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
__releases(rq->lock)
__releases(p->pi_lock)
{
- raw_spin_unlock(&rq->lock);
+ rq_unlock(rq);
raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
}

@@ -360,7 +380,7 @@ static struct rq *this_rq_lock(void)

local_irq_disable();
rq = this_rq();
- raw_spin_lock(&rq->lock);
+ rq_lock(rq);

return rq;
}
@@ -386,10 +406,10 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)

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;
}
@@ -411,10 +431,10 @@ 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);
}

/*
@@ -515,7 +535,7 @@ 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;
@@ -539,10 +559,10 @@ 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
@@ -837,7 +857,7 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
}
#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))
@@ -967,8 +987,10 @@ void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
* 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
@@ -1479,7 +1501,7 @@ 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);
@@ -1487,7 +1509,7 @@ static void sched_ttwu_pending(void)
ttwu_do_activate(rq, p, 0);
}

- raw_spin_unlock(&rq->lock);
+ rq_unlock(rq);
}

void scheduler_ipi(void)
@@ -1555,9 +1577,9 @@ static void ttwu_queue(struct task_struct *p, int cpu)
}
#endif

- raw_spin_lock(&rq->lock);
+ rq_lock(rq);
ttwu_do_activate(rq, p, 0);
- raw_spin_unlock(&rq->lock);
+ rq_unlock(rq);
}

/**
@@ -1648,12 +1670,12 @@ static void try_to_wake_up_local(struct task_struct *p)
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))
@@ -2170,10 +2192,12 @@ static inline void post_schedule(struct rq *rq)
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;
}
@@ -2423,11 +2447,11 @@ 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();

@@ -2670,7 +2694,8 @@ 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)) {
@@ -2718,8 +2743,10 @@ 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);

@@ -4077,9 +4104,8 @@ 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();
@@ -4476,7 +4502,8 @@ void init_idle(struct task_struct *idle, int cpu)
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;
@@ -4502,7 +4529,8 @@ void init_idle(struct task_struct *idle, int cpu)
#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);
@@ -4801,11 +4829,11 @@ static void migrate_tasks(unsigned int dead_cpu)

/* 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;
@@ -5040,27 +5068,31 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)

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:
@@ -5356,7 +5388,8 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd)
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;
@@ -5382,7 +5415,8 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd)
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);
@@ -6860,7 +6894,7 @@ 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;
@@ -7771,13 +7805,13 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
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();
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 27ef40925525..4682acb7976a 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -514,7 +514,8 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
dl_timer);
struct task_struct *p = dl_task_of(dl_se);
struct rq *rq = task_rq(p);
- raw_spin_lock(&rq->lock);
+
+ rq_lock(rq);

/*
* We need to take care of a possible races here. In fact, the
@@ -544,7 +545,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
#endif
}
unlock:
- raw_spin_unlock(&rq->lock);
+ rq_unlock(rq);

return HRTIMER_NORESTART;
}
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index f3344c31632a..9a12ea15469f 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -188,7 +188,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
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);
@@ -196,7 +196,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
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",
@@ -302,7 +302,8 @@ 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]);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7e9bd0b1fa9e..60db6c533873 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3369,7 +3369,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
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;

@@ -3386,7 +3386,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
unthrottle_cfs_rq(cfs_rq);

next:
- raw_spin_unlock(&rq->lock);
+ raw_spin_unlock(&rq->__lock);

if (!remaining)
break;
@@ -4846,7 +4846,8 @@ static void yield_task_fair(struct rq *rq)
* 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);
@@ -5375,7 +5376,8 @@ static void update_blocked_averages(int cpu)
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
@@ -5390,7 +5392,8 @@ static void update_blocked_averages(int cpu)
__update_blocked_averages_cpu(cfs_rq->tg, rq->cpu);
}

- raw_spin_unlock_irqrestore(&rq->lock, flags);
+ rq_unlock(rq);
+ local_irq_restore(flags);
}

/*
@@ -6565,7 +6568,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
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
@@ -6573,7 +6576,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
*/
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;
@@ -6589,7 +6592,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
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),
@@ -6664,7 +6667,7 @@ static int idle_balance(struct rq *this_rq)
/*
* 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();
@@ -6702,7 +6705,7 @@ static int idle_balance(struct rq *this_rq)
}
rcu_read_unlock();

- raw_spin_lock(&this_rq->lock);
+ raw_spin_lock(&this_rq->__lock);

/*
* While browsing the domains, we released the rq lock.
@@ -6753,7 +6756,7 @@ static int active_load_balance_cpu_stop(void *data)
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() ||
@@ -6803,7 +6806,7 @@ static int active_load_balance_cpu_stop(void *data)
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;
}

@@ -7091,10 +7094,12 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)

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);

@@ -7258,7 +7263,8 @@ static void task_fork_fair(struct task_struct *p)
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);

@@ -7292,7 +7298,8 @@ static void task_fork_fair(struct task_struct *p)

se->vruntime -= cfs_rq->min_vruntime;

- raw_spin_unlock_irqrestore(&rq->lock, flags);
+ rq_unlock(rq);
+ local_irq_restore(flags);
}

/*
@@ -7533,9 +7540,9 @@ void unregister_fair_sched_group(struct task_group *tg, int cpu)
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,
@@ -7595,13 +7602,16 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares)

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:
diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c
index 879f2b75266a..91cee2d0bf18 100644
--- a/kernel/sched/idle_task.c
+++ b/kernel/sched/idle_task.c
@@ -39,10 +39,10 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev)
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)
diff --git a/kernel/sched/proc.c b/kernel/sched/proc.c
index 16f5a30f9c88..d08b4f715189 100644
--- 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 */

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index d8cdf1618551..2845c9d172f0 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -774,7 +774,7 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
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;

@@ -807,7 +807,7 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)

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))
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c9007f28d3a2..7a20e203c057 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -517,7 +517,7 @@ extern struct root_domain def_root_domain;
*/
struct rq {
/* runqueue lock: */
- raw_spinlock_t lock;
+ raw_spinlock_t __lock;

/*
* nr_running and cpu_load should be in the same cacheline because
@@ -538,7 +538,6 @@ 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;
@@ -568,8 +567,11 @@ 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;

@@ -645,6 +647,24 @@ 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
@@ -664,12 +684,26 @@ 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
@@ -990,16 +1024,17 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
#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 */
@@ -1013,7 +1048,7 @@ static inline void prepare_lock_switch(struct rq *rq, struct task_struct *next)
*/
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)
@@ -1313,12 +1348,12 @@ static inline void double_rq_lock(struct rq *rq1, struct rq *rq2);
* 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;
@@ -1332,22 +1367,22 @@ static inline int _double_lock_balance(struct rq *this_rq, struct rq *busiest)
* 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;
@@ -1355,25 +1390,11 @@ static inline int _double_lock_balance(struct rq *this_rq, struct rq *busiest)

#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)
@@ -1406,15 +1427,15 @@ static inline void double_rq_lock(struct rq *rq1, struct rq *rq2)
{
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);
}
}
}
@@ -1429,9 +1450,9 @@ static inline void double_rq_unlock(struct rq *rq1, struct rq *rq2)
__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);
}
@@ -1450,7 +1471,7 @@ static inline void double_rq_lock(struct rq *rq1, struct rq *rq2)
{
BUG_ON(!irqs_disabled());
BUG_ON(rq1 != rq2);
- raw_spin_lock(&rq1->lock);
+ raw_spin_lock(&rq1->__lock);
__acquire(rq2->lock); /* Fake it out ;) */
}

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index dd7f8858188a..d8222df9f839 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -779,6 +779,13 @@ 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
--
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