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   1 /*
   2  * trace task wakeup timings
   3  *
   4  * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
   5  * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
   6  *
   7  * Based on code from the latency_tracer, that is:
   8  *
   9  *  Copyright (C) 2004-2006 Ingo Molnar
  10  *  Copyright (C) 2004 William Lee Irwin III
  11  */
  12 #include <linux/module.h>
  13 #include <linux/fs.h>
  14 #include <linux/debugfs.h>
  15 #include <linux/kallsyms.h>
  16 #include <linux/uaccess.h>
  17 #include <linux/ftrace.h>
  18
  19 #include "trace.h"
  20
  21 static struct trace_array       *wakeup_trace;
  22 static int __read_mostly        tracer_enabled;
  23
  24 static struct task_struct       *wakeup_task;
  25 static int                      wakeup_cpu;
  26 static unsigned                 wakeup_prio = -1;
  27
  28 static DEFINE_SPINLOCK(wakeup_lock);
  29
  30 static void __wakeup_reset(struct trace_array *tr);
  31
  32 /*
  33  * Should this new latency be reported/recorded?
  34  */
  35 static int report_latency(cycle_t delta)
  36 {
  37         if (tracing_thresh) {
  38                 if (delta < tracing_thresh)
  39                         return 0;
  40         } else {
  41                 if (delta <= tracing_max_latency)
  42                         return 0;
  43         }
  44         return 1;
  45 }
  46
  47 void
  48 wakeup_sched_switch(struct task_struct *prev, struct task_struct *next)
  49 {
  50         unsigned long latency = 0, t0 = 0, t1 = 0;
  51         struct trace_array *tr = wakeup_trace;
  52         struct trace_array_cpu *data;
  53         cycle_t T0, T1, delta;
  54         unsigned long flags;
  55         long disabled;
  56         int cpu;
  57
  58         if (unlikely(!tracer_enabled))
  59                 return;
  60
  61         /*
  62          * When we start a new trace, we set wakeup_task to NULL
  63          * and then set tracer_enabled = 1. We want to make sure
  64          * that another CPU does not see the tracer_enabled = 1
  65          * and the wakeup_task with an older task, that might
  66          * actually be the same as next.
  67          */
  68         smp_rmb();
  69
  70         if (next != wakeup_task)
  71                 return;
  72
  73         /* The task we are waitng for is waking up */
  74         data = tr->data[wakeup_cpu];
  75
  76         /* disable local data, not wakeup_cpu data */
  77         cpu = raw_smp_processor_id();
  78         disabled = atomic_inc_return(&tr->data[cpu]->disabled);
  79         if (likely(disabled != 1))
  80                 goto out;
  81
  82         spin_lock_irqsave(&wakeup_lock, flags);
  83
  84         /* We could race with grabbing wakeup_lock */
  85         if (unlikely(!tracer_enabled || next != wakeup_task))
  86                 goto out_unlock;
  87
  88         trace_function(tr, data, CALLER_ADDR1, CALLER_ADDR2, flags);
  89
  90         /*
  91          * usecs conversion is slow so we try to delay the conversion
  92          * as long as possible:
  93          */
  94         T0 = data->preempt_timestamp;
  95         T1 = ftrace_now(cpu);
  96         delta = T1-T0;
  97
  98         if (!report_latency(delta))
  99                 goto out_unlock;
 100
 101         latency = nsecs_to_usecs(delta);
 102
 103         tracing_max_latency = delta;
 104         t0 = nsecs_to_usecs(T0);
 105         t1 = nsecs_to_usecs(T1);
 106
 107         update_max_tr(tr, wakeup_task, wakeup_cpu);
 108
 109 out_unlock:
 110         __wakeup_reset(tr);
 111         spin_unlock_irqrestore(&wakeup_lock, flags);
 112 out:
 113         atomic_dec(&tr->data[cpu]->disabled);
 114 }
 115
 116 static void __wakeup_reset(struct trace_array *tr)
 117 {
 118         struct trace_array_cpu *data;
 119         int cpu;
 120
 121         assert_spin_locked(&wakeup_lock);
 122
 123         for_each_possible_cpu(cpu) {
 124                 data = tr->data[cpu];
 125                 tracing_reset(data);
 126         }
 127
 128         wakeup_cpu = -1;
 129         wakeup_prio = -1;
 130
 131         if (wakeup_task)
 132                 put_task_struct(wakeup_task);
 133
 134         wakeup_task = NULL;
 135 }
 136
 137 static void wakeup_reset(struct trace_array *tr)
 138 {
 139         unsigned long flags;
 140
 141         spin_lock_irqsave(&wakeup_lock, flags);
 142         __wakeup_reset(tr);
 143         spin_unlock_irqrestore(&wakeup_lock, flags);
 144 }
 145
 146 static void
 147 wakeup_check_start(struct trace_array *tr, struct task_struct *p,
 148                    struct task_struct *curr)
 149 {
 150         int cpu = smp_processor_id();
 151         unsigned long flags;
 152         long disabled;
 153
 154         if (likely(!rt_task(p)) ||
 155                         p->prio >= wakeup_prio ||
 156                         p->prio >= curr->prio)
 157                 return;
 158
 159         disabled = atomic_inc_return(&tr->data[cpu]->disabled);
 160         if (unlikely(disabled != 1))
 161                 goto out;
 162
 163         /* interrupts should be off from try_to_wake_up */
 164         spin_lock(&wakeup_lock);
 165
 166         /* check for races. */
 167         if (!tracer_enabled || p->prio >= wakeup_prio)
 168                 goto out_locked;
 169
 170         /* reset the trace */
 171         __wakeup_reset(tr);
 172
 173         wakeup_cpu = task_cpu(p);
 174         wakeup_prio = p->prio;
 175
 176         wakeup_task = p;
 177         get_task_struct(wakeup_task);
 178
 179         local_save_flags(flags);
 180
 181         tr->data[wakeup_cpu]->preempt_timestamp = ftrace_now(cpu);
 182         trace_function(tr, tr->data[wakeup_cpu],
 183                        CALLER_ADDR1, CALLER_ADDR2, flags);
 184
 185 out_locked:
 186         spin_unlock(&wakeup_lock);
 187 out:
 188         atomic_dec(&tr->data[cpu]->disabled);
 189 }
 190
 191 void wakeup_sched_wakeup(struct task_struct *wakee, struct task_struct *curr)
 192 {
 193         if (likely(!tracer_enabled))
 194                 return;
 195
 196         tracing_record_cmdline(curr);
 197         tracing_record_cmdline(wakee);
 198
 199         wakeup_check_start(wakeup_trace, wakee, curr);
 200 }
 201
 202 static void start_wakeup_tracer(struct trace_array *tr)
 203 {
 204         wakeup_reset(tr);
 205
 206         /*
 207          * Don't let the tracer_enabled = 1 show up before
 208          * the wakeup_task is reset. This may be overkill since
 209          * wakeup_reset does a spin_unlock after setting the
 210          * wakeup_task to NULL, but I want to be safe.
 211          * This is a slow path anyway.
 212          */
 213         smp_wmb();
 214
 215         tracer_enabled = 1;
 216
 217         return;
 218 }
 219
 220 static void stop_wakeup_tracer(struct trace_array *tr)
 221 {
 222         tracer_enabled = 0;
 223 }
 224
 225 static void wakeup_tracer_init(struct trace_array *tr)
 226 {
 227         wakeup_trace = tr;
 228
 229         if (tr->ctrl)
 230                 start_wakeup_tracer(tr);
 231 }
 232
 233 static void wakeup_tracer_reset(struct trace_array *tr)
 234 {
 235         if (tr->ctrl) {
 236                 stop_wakeup_tracer(tr);
 237                 /* make sure we put back any tasks we are tracing */
 238                 wakeup_reset(tr);
 239         }
 240 }
 241
 242 static void wakeup_tracer_ctrl_update(struct trace_array *tr)
 243 {
 244         if (tr->ctrl)
 245                 start_wakeup_tracer(tr);
 246         else
 247                 stop_wakeup_tracer(tr);
 248 }
 249
 250 static void wakeup_tracer_open(struct trace_iterator *iter)
 251 {
 252         /* stop the trace while dumping */
 253         if (iter->tr->ctrl)
 254                 stop_wakeup_tracer(iter->tr);
 255 }
 256
 257 static void wakeup_tracer_close(struct trace_iterator *iter)
 258 {
 259         /* forget about any processes we were recording */
 260         if (iter->tr->ctrl)
 261                 start_wakeup_tracer(iter->tr);
 262 }
 263
 264 static struct tracer wakeup_tracer __read_mostly =
 265 {
 266         .name           = "wakeup",
 267         .init           = wakeup_tracer_init,
 268         .reset          = wakeup_tracer_reset,
 269         .open           = wakeup_tracer_open,
 270         .close          = wakeup_tracer_close,
 271         .ctrl_update    = wakeup_tracer_ctrl_update,
 272         .print_max      = 1,
 273 #ifdef CONFIG_FTRACE_SELFTEST
 274         .selftest    = trace_selftest_startup_wakeup,
 275 #endif
 276 };
 277
 278 __init static int init_wakeup_tracer(void)
 279 {
 280         int ret;
 281
 282         ret = register_tracer(&wakeup_tracer);
 283         if (ret)
 284                 return ret;
 285
 286         return 0;
 287 }
 288 device_initcall(init_wakeup_tracer);