trace_sched_wakeup.c

/*
 * trace task wakeup timings
 *
 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
 * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
 *
 * Based on code from the latency_tracer, that is:
 *
 *  Copyright (C) 2004-2006 Ingo Molnar
 *  Copyright (C) 2004 William Lee Irwin III
 */
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/debugfs.h>
#include <linux/kallsyms.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>

#include "trace.h"

static struct trace_array	*wakeup_trace;
static int __read_mostly	tracer_enabled;

static struct task_struct	*wakeup_task;
static int			wakeup_cpu;
static unsigned			wakeup_prio = -1;

static DEFINE_SPINLOCK(wakeup_lock);

static void notrace __wakeup_reset(struct trace_array *tr);

/*
 * Should this new latency be reported/recorded?
 */
static int notrace report_latency(cycle_t delta)
{
	if (tracing_thresh) {
		if (delta < tracing_thresh)
			return 0;
	} else {
		if (delta <= tracing_max_latency)
			return 0;
	}
	return 1;
}

void notrace
wakeup_sched_switch(struct task_struct *prev, struct task_struct *next)
{
	unsigned long latency = 0, t0 = 0, t1 = 0;
	struct trace_array *tr = wakeup_trace;
	struct trace_array_cpu *data;
	cycle_t T0, T1, delta;
	unsigned long flags;
	long disabled;
	int cpu;

	if (unlikely(!tracer_enabled))
		return;

	/*
	 * When we start a new trace, we set wakeup_task to NULL
	 * and then set tracer_enabled = 1. We want to make sure
	 * that another CPU does not see the tracer_enabled = 1
	 * and the wakeup_task with an older task, that might
	 * actually be the same as next.
	 */
	smp_rmb();

	if (next != wakeup_task)
		return;

	/* The task we are waitng for is waking up */
	data = tr->data[wakeup_cpu];

	/* disable local data, not wakeup_cpu data */
	cpu = raw_smp_processor_id();
	disabled = atomic_inc_return(&tr->data[cpu]->disabled);
	if (likely(disabled != 1))
		goto out;

	spin_lock_irqsave(&wakeup_lock, flags);

	/* We could race with grabbing wakeup_lock */
	if (unlikely(!tracer_enabled || next != wakeup_task))
		goto out_unlock;

	ftrace(tr, data, CALLER_ADDR1, CALLER_ADDR2, flags);

	/*
	 * usecs conversion is slow so we try to delay the conversion
	 * as long as possible:
	 */
	T0 = data->preempt_timestamp;
	T1 = ftrace_now(cpu);
	delta = T1-T0;

	if (!report_latency(delta))
		goto out_unlock;

	latency = nsecs_to_usecs(delta);

	tracing_max_latency = delta;
	t0 = nsecs_to_usecs(T0);
	t1 = nsecs_to_usecs(T1);

	update_max_tr(tr, wakeup_task, wakeup_cpu);

	if (tracing_thresh) {
		printk(KERN_INFO "(%16s-%-5d|#%d):"
			" %lu us wakeup latency violates %lu us threshold.\n",
				wakeup_task->comm, wakeup_task->pid,
				raw_smp_processor_id(),
				latency, nsecs_to_usecs(tracing_thresh));
	} else {
		printk(KERN_INFO "(%16s-%-5d|#%d):"
			" new %lu us maximum wakeup latency.\n",
				wakeup_task->comm, wakeup_task->pid,
				cpu, latency);
	}

out_unlock:
	__wakeup_reset(tr);
	spin_unlock_irqrestore(&wakeup_lock, flags);
out:
	atomic_dec(&tr->data[cpu]->disabled);
}

static void notrace __wakeup_reset(struct trace_array *tr)
{
	struct trace_array_cpu *data;
	int cpu;

	assert_spin_locked(&wakeup_lock);

	for_each_possible_cpu(cpu) {
		data = tr->data[cpu];
		tracing_reset(data);
	}

	wakeup_cpu = -1;
	wakeup_prio = -1;

	if (wakeup_task)
		put_task_struct(wakeup_task);

	wakeup_task = NULL;
}

static void notrace wakeup_reset(struct trace_array *tr)
{
	unsigned long flags;

	spin_lock_irqsave(&wakeup_lock, flags);
	__wakeup_reset(tr);
	spin_unlock_irqrestore(&wakeup_lock, flags);
}

static notrace void
wakeup_check_start(struct trace_array *tr, struct task_struct *p,
		   struct task_struct *curr)
{
	int cpu = smp_processor_id();
	unsigned long flags;
	long disabled;

	if (likely(!rt_task(p)) ||
			p->prio >= wakeup_prio ||
			p->prio >= curr->prio)
		return;

	disabled = atomic_inc_return(&tr->data[cpu]->disabled);
	if (unlikely(disabled != 1))
		goto out;

	/* interrupts should be off from try_to_wake_up */
	spin_lock(&wakeup_lock);

	/* check for races. */
	if (!tracer_enabled || p->prio >= wakeup_prio)
		goto out_locked;

	/* reset the trace */
	__wakeup_reset(tr);

	wakeup_cpu = task_cpu(p);
	wakeup_prio = p->prio;

	wakeup_task = p;
	get_task_struct(wakeup_task);

	local_save_flags(flags);

	tr->data[wakeup_cpu]->preempt_timestamp = ftrace_now(cpu);
	ftrace(tr, tr->data[wakeup_cpu], CALLER_ADDR1, CALLER_ADDR2, flags);

out_locked:
	spin_unlock(&wakeup_lock);
out:
	atomic_dec(&tr->data[cpu]->disabled);
}

notrace void
ftrace_wake_up_task(struct task_struct *wakee, struct task_struct *curr)
{
	if (likely(!tracer_enabled))
		return;

	wakeup_check_start(wakeup_trace, wakee, curr);
}

notrace void
ftrace_wake_up_new_task(struct task_struct *wakee, struct task_struct *curr)
{
	if (likely(!tracer_enabled))
		return;

	wakeup_check_start(wakeup_trace, wakee, curr);
}

static notrace void start_wakeup_tracer(struct trace_array *tr)
{
	wakeup_reset(tr);

	/*
	 * Don't let the tracer_enabled = 1 show up before
	 * the wakeup_task is reset. This may be overkill since
	 * wakeup_reset does a spin_unlock after setting the
	 * wakeup_task to NULL, but I want to be safe.
	 * This is a slow path anyway.
	 */
	smp_wmb();

	tracer_enabled = 1;

	return;
}

static notrace void stop_wakeup_tracer(struct trace_array *tr)
{
	tracer_enabled = 0;
}

static notrace void wakeup_tracer_init(struct trace_array *tr)
{
	wakeup_trace = tr;

	if (tr->ctrl)
		start_wakeup_tracer(tr);
}

static notrace void wakeup_tracer_reset(struct trace_array *tr)
{
	if (tr->ctrl) {
		stop_wakeup_tracer(tr);
		/* make sure we put back any tasks we are tracing */
		wakeup_reset(tr);
	}
}

static void wakeup_tracer_ctrl_update(struct trace_array *tr)
{
	if (tr->ctrl)
		start_wakeup_tracer(tr);
	else
		stop_wakeup_tracer(tr);
}

static void notrace wakeup_tracer_open(struct trace_iterator *iter)
{
	/* stop the trace while dumping */
	if (iter->tr->ctrl)
		stop_wakeup_tracer(iter->tr);
}

static void notrace wakeup_tracer_close(struct trace_iterator *iter)
{
	/* forget about any processes we were recording */
	if (iter->tr->ctrl)
		start_wakeup_tracer(iter->tr);
}

static struct tracer wakeup_tracer __read_mostly =
{
	.name		= "wakeup",
	.init		= wakeup_tracer_init,
	.reset		= wakeup_tracer_reset,
	.open		= wakeup_tracer_open,
	.close		= wakeup_tracer_close,
	.ctrl_update	= wakeup_tracer_ctrl_update,
	.print_max	= 1,
#ifdef CONFIG_FTRACE_SELFTEST
	.selftest    = trace_selftest_startup_wakeup,
#endif
};

__init static int init_wakeup_tracer(void)
{
	int ret;

	ret = register_tracer(&wakeup_tracer);
	if (ret)
		return ret;

	return 0;
}
device_initcall(init_wakeup_tracer);