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sched: Introduce the 'trace_sched_waking' tracepoint
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Mathieu reported that since 317f394 ("sched: Move the second half
of ttwu() to the remote cpu") trace_sched_wakeup() can happen out of
context of the waker.

This is a problem when you want to analyse wakeup paths because it is
now very hard to correlate the wakeup event to whoever issued the
wakeup.

OTOH trace_sched_wakeup() is issued at the point where we set
p->state = TASK_RUNNING, which is right were we hand the task off to
the scheduler, so this is an important point when looking at
scheduling behaviour, up to here its been the wakeup path everything
hereafter is due to scheduler policy.

To bridge this gap, introduce a second tracepoint: trace_sched_waking.
It is guaranteed to be called in the waker context.

Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Francis Giraldeau <francis.giraldeau@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150609091336.GQ3644@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Peter Zijlstra authored and Ingo Molnar committed Aug 3, 2015
1 parent 9d7fb04 commit fbd705a
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Showing 4 changed files with 30 additions and 14 deletions.
30 changes: 21 additions & 9 deletions include/trace/events/sched.h
Original file line number Diff line number Diff line change
Expand Up @@ -55,9 +55,9 @@ TRACE_EVENT(sched_kthread_stop_ret,
*/
DECLARE_EVENT_CLASS(sched_wakeup_template,

TP_PROTO(struct task_struct *p, int success),
TP_PROTO(struct task_struct *p),

TP_ARGS(__perf_task(p), success),
TP_ARGS(__perf_task(p)),

TP_STRUCT__entry(
__array( char, comm, TASK_COMM_LEN )
Expand All @@ -71,25 +71,37 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,
memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
__entry->pid = p->pid;
__entry->prio = p->prio;
__entry->success = success;
__entry->success = 1; /* rudiment, kill when possible */
__entry->target_cpu = task_cpu(p);
),

TP_printk("comm=%s pid=%d prio=%d success=%d target_cpu=%03d",
TP_printk("comm=%s pid=%d prio=%d target_cpu=%03d",
__entry->comm, __entry->pid, __entry->prio,
__entry->success, __entry->target_cpu)
__entry->target_cpu)
);

/*
* Tracepoint called when waking a task; this tracepoint is guaranteed to be
* called from the waking context.
*/
DEFINE_EVENT(sched_wakeup_template, sched_waking,
TP_PROTO(struct task_struct *p),
TP_ARGS(p));

/*
* Tracepoint called when the task is actually woken; p->state == TASK_RUNNNG.
* It it not always called from the waking context.
*/
DEFINE_EVENT(sched_wakeup_template, sched_wakeup,
TP_PROTO(struct task_struct *p, int success),
TP_ARGS(p, success));
TP_PROTO(struct task_struct *p),
TP_ARGS(p));

/*
* Tracepoint for waking up a new task:
*/
DEFINE_EVENT(sched_wakeup_template, sched_wakeup_new,
TP_PROTO(struct task_struct *p, int success),
TP_ARGS(p, success));
TP_PROTO(struct task_struct *p),
TP_ARGS(p));

#ifdef CREATE_TRACE_POINTS
static inline long __trace_sched_switch_state(struct task_struct *p)
Expand Down
10 changes: 7 additions & 3 deletions kernel/sched/core.c
Original file line number Diff line number Diff line change
Expand Up @@ -1654,9 +1654,9 @@ static void
ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
{
check_preempt_curr(rq, p, wake_flags);
trace_sched_wakeup(p, true);

p->state = TASK_RUNNING;
trace_sched_wakeup(p);

#ifdef CONFIG_SMP
if (p->sched_class->task_woken) {
/*
Expand Down Expand Up @@ -1874,6 +1874,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
if (!(p->state & state))
goto out;

trace_sched_waking(p);

success = 1; /* we're going to change ->state */
cpu = task_cpu(p);

Expand Down Expand Up @@ -1949,6 +1951,8 @@ static void try_to_wake_up_local(struct task_struct *p)
if (!(p->state & TASK_NORMAL))
goto out;

trace_sched_waking(p);

if (!task_on_rq_queued(p))
ttwu_activate(rq, p, ENQUEUE_WAKEUP);

Expand Down Expand Up @@ -2307,7 +2311,7 @@ void wake_up_new_task(struct task_struct *p)
rq = __task_rq_lock(p);
activate_task(rq, p, 0);
p->on_rq = TASK_ON_RQ_QUEUED;
trace_sched_wakeup_new(p, true);
trace_sched_wakeup_new(p);
check_preempt_curr(rq, p, WF_FORK);
#ifdef CONFIG_SMP
if (p->sched_class->task_woken)
Expand Down
2 changes: 1 addition & 1 deletion kernel/trace/trace_sched_switch.c
Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ probe_sched_switch(void *ignore, struct task_struct *prev, struct task_struct *n
}

static void
probe_sched_wakeup(void *ignore, struct task_struct *wakee, int success)
probe_sched_wakeup(void *ignore, struct task_struct *wakee)
{
if (unlikely(!sched_ref))
return;
Expand Down
2 changes: 1 addition & 1 deletion kernel/trace/trace_sched_wakeup.c
Original file line number Diff line number Diff line change
Expand Up @@ -514,7 +514,7 @@ static void wakeup_reset(struct trace_array *tr)
}

static void
probe_wakeup(void *ignore, struct task_struct *p, int success)
probe_wakeup(void *ignore, struct task_struct *p)
{
struct trace_array_cpu *data;
int cpu = smp_processor_id();
Expand Down

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