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 #include <trace/sched.h> 19 20 #include "trace.h" 21 22 static struct trace_array *wakeup_trace; 23 static int __read_mostly tracer_enabled; 24 25 static struct task_struct *wakeup_task; 26 static int wakeup_cpu; 27 static unsigned wakeup_prio = -1; 28 29 static raw_spinlock_t wakeup_lock = 30 (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED; 31 32 static void __wakeup_reset(struct trace_array *tr); 33 34 #ifdef CONFIG_FUNCTION_TRACER 35 /* 36 * irqsoff uses its own tracer function to keep the overhead down: 37 */ 38 static void 39 wakeup_tracer_call(unsigned long ip, unsigned long parent_ip) 40 { 41 struct trace_array *tr = wakeup_trace; 42 struct trace_array_cpu *data; 43 unsigned long flags; 44 long disabled; 45 int resched; 46 int cpu; 47 int pc; 48 49 if (likely(!wakeup_task)) 50 return; 51 52 pc = preempt_count(); 53 resched = need_resched(); 54 preempt_disable_notrace(); 55 56 cpu = raw_smp_processor_id(); 57 data = tr->data[cpu]; 58 disabled = atomic_inc_return(&data->disabled); 59 if (unlikely(disabled != 1)) 60 goto out; 61 62 local_irq_save(flags); 63 __raw_spin_lock(&wakeup_lock); 64 65 if (unlikely(!wakeup_task)) 66 goto unlock; 67 68 /* 69 * The task can't disappear because it needs to 70 * wake up first, and we have the wakeup_lock. 71 */ 72 if (task_cpu(wakeup_task) != cpu) 73 goto unlock; 74 75 trace_function(tr, data, ip, parent_ip, flags, pc); 76 77 unlock: 78 __raw_spin_unlock(&wakeup_lock); 79 local_irq_restore(flags); 80 81 out: 82 atomic_dec(&data->disabled); 83 84 /* 85 * To prevent recursion from the scheduler, if the 86 * resched flag was set before we entered, then 87 * don't reschedule. 88 */ 89 if (resched) 90 preempt_enable_no_resched_notrace(); 91 else 92 preempt_enable_notrace(); 93 } 94 95 static struct ftrace_ops trace_ops __read_mostly = 96 { 97 .func = wakeup_tracer_call, 98 }; 99 #endif /* CONFIG_FUNCTION_TRACER */ 100 101 /* 102 * Should this new latency be reported/recorded? 103 */ 104 static int report_latency(cycle_t delta) 105 { 106 if (tracing_thresh) { 107 if (delta < tracing_thresh) 108 return 0; 109 } else { 110 if (delta <= tracing_max_latency) 111 return 0; 112 } 113 return 1; 114 } 115 116 static void notrace 117 probe_wakeup_sched_switch(struct rq *rq, struct task_struct *prev, 118 struct task_struct *next) 119 { 120 unsigned long latency = 0, t0 = 0, t1 = 0; 121 struct trace_array_cpu *data; 122 cycle_t T0, T1, delta; 123 unsigned long flags; 124 long disabled; 125 int cpu; 126 int pc; 127 128 tracing_record_cmdline(prev); 129 130 if (unlikely(!tracer_enabled)) 131 return; 132 133 /* 134 * When we start a new trace, we set wakeup_task to NULL 135 * and then set tracer_enabled = 1. We want to make sure 136 * that another CPU does not see the tracer_enabled = 1 137 * and the wakeup_task with an older task, that might 138 * actually be the same as next. 139 */ 140 smp_rmb(); 141 142 if (next != wakeup_task) 143 return; 144 145 pc = preempt_count(); 146 147 /* The task we are waiting for is waking up */ 148 data = wakeup_trace->data[wakeup_cpu]; 149 150 /* disable local data, not wakeup_cpu data */ 151 cpu = raw_smp_processor_id(); 152 disabled = atomic_inc_return(&wakeup_trace->data[cpu]->disabled); 153 if (likely(disabled != 1)) 154 goto out; 155 156 local_irq_save(flags); 157 __raw_spin_lock(&wakeup_lock); 158 159 /* We could race with grabbing wakeup_lock */ 160 if (unlikely(!tracer_enabled || next != wakeup_task)) 161 goto out_unlock; 162 163 trace_function(wakeup_trace, data, CALLER_ADDR1, CALLER_ADDR2, flags, pc); 164 165 /* 166 * usecs conversion is slow so we try to delay the conversion 167 * as long as possible: 168 */ 169 T0 = data->preempt_timestamp; 170 T1 = ftrace_now(cpu); 171 delta = T1-T0; 172 173 if (!report_latency(delta)) 174 goto out_unlock; 175 176 latency = nsecs_to_usecs(delta); 177 178 tracing_max_latency = delta; 179 t0 = nsecs_to_usecs(T0); 180 t1 = nsecs_to_usecs(T1); 181 182 update_max_tr(wakeup_trace, wakeup_task, wakeup_cpu); 183 184 out_unlock: 185 __wakeup_reset(wakeup_trace); 186 __raw_spin_unlock(&wakeup_lock); 187 local_irq_restore(flags); 188 out: 189 atomic_dec(&wakeup_trace->data[cpu]->disabled); 190 } 191 192 static void __wakeup_reset(struct trace_array *tr) 193 { 194 struct trace_array_cpu *data; 195 int cpu; 196 197 for_each_possible_cpu(cpu) { 198 data = tr->data[cpu]; 199 tracing_reset(tr, cpu); 200 } 201 202 wakeup_cpu = -1; 203 wakeup_prio = -1; 204 205 if (wakeup_task) 206 put_task_struct(wakeup_task); 207 208 wakeup_task = NULL; 209 } 210 211 static void wakeup_reset(struct trace_array *tr) 212 { 213 unsigned long flags; 214 215 local_irq_save(flags); 216 __raw_spin_lock(&wakeup_lock); 217 __wakeup_reset(tr); 218 __raw_spin_unlock(&wakeup_lock); 219 local_irq_restore(flags); 220 } 221 222 static void 223 probe_wakeup(struct rq *rq, struct task_struct *p) 224 { 225 int cpu = smp_processor_id(); 226 unsigned long flags; 227 long disabled; 228 int pc; 229 230 if (likely(!tracer_enabled)) 231 return; 232 233 tracing_record_cmdline(p); 234 tracing_record_cmdline(current); 235 236 if (likely(!rt_task(p)) || 237 p->prio >= wakeup_prio || 238 p->prio >= current->prio) 239 return; 240 241 pc = preempt_count(); 242 disabled = atomic_inc_return(&wakeup_trace->data[cpu]->disabled); 243 if (unlikely(disabled != 1)) 244 goto out; 245 246 /* interrupts should be off from try_to_wake_up */ 247 __raw_spin_lock(&wakeup_lock); 248 249 /* check for races. */ 250 if (!tracer_enabled || p->prio >= wakeup_prio) 251 goto out_locked; 252 253 /* reset the trace */ 254 __wakeup_reset(wakeup_trace); 255 256 wakeup_cpu = task_cpu(p); 257 wakeup_prio = p->prio; 258 259 wakeup_task = p; 260 get_task_struct(wakeup_task); 261 262 local_save_flags(flags); 263 264 wakeup_trace->data[wakeup_cpu]->preempt_timestamp = ftrace_now(cpu); 265 trace_function(wakeup_trace, wakeup_trace->data[wakeup_cpu], 266 CALLER_ADDR1, CALLER_ADDR2, flags, pc); 267 268 out_locked: 269 __raw_spin_unlock(&wakeup_lock); 270 out: 271 atomic_dec(&wakeup_trace->data[cpu]->disabled); 272 } 273 274 static void start_wakeup_tracer(struct trace_array *tr) 275 { 276 int ret; 277 278 ret = register_trace_sched_wakeup(probe_wakeup); 279 if (ret) { 280 pr_info("wakeup trace: Couldn't activate tracepoint" 281 " probe to kernel_sched_wakeup\n"); 282 return; 283 } 284 285 ret = register_trace_sched_wakeup_new(probe_wakeup); 286 if (ret) { 287 pr_info("wakeup trace: Couldn't activate tracepoint" 288 " probe to kernel_sched_wakeup_new\n"); 289 goto fail_deprobe; 290 } 291 292 ret = register_trace_sched_switch(probe_wakeup_sched_switch); 293 if (ret) { 294 pr_info("sched trace: Couldn't activate tracepoint" 295 " probe to kernel_sched_schedule\n"); 296 goto fail_deprobe_wake_new; 297 } 298 299 wakeup_reset(tr); 300 301 /* 302 * Don't let the tracer_enabled = 1 show up before 303 * the wakeup_task is reset. This may be overkill since 304 * wakeup_reset does a spin_unlock after setting the 305 * wakeup_task to NULL, but I want to be safe. 306 * This is a slow path anyway. 307 */ 308 smp_wmb(); 309 310 register_ftrace_function(&trace_ops); 311 312 tracer_enabled = 1; 313 314 return; 315 fail_deprobe_wake_new: 316 unregister_trace_sched_wakeup_new(probe_wakeup); 317 fail_deprobe: 318 unregister_trace_sched_wakeup(probe_wakeup); 319 } 320 321 static void stop_wakeup_tracer(struct trace_array *tr) 322 { 323 tracer_enabled = 0; 324 unregister_ftrace_function(&trace_ops); 325 unregister_trace_sched_switch(probe_wakeup_sched_switch); 326 unregister_trace_sched_wakeup_new(probe_wakeup); 327 unregister_trace_sched_wakeup(probe_wakeup); 328 } 329 330 static void wakeup_tracer_init(struct trace_array *tr) 331 { 332 wakeup_trace = tr; 333 334 if (tr->ctrl) 335 start_wakeup_tracer(tr); 336 } 337 338 static void wakeup_tracer_reset(struct trace_array *tr) 339 { 340 if (tr->ctrl) { 341 stop_wakeup_tracer(tr); 342 /* make sure we put back any tasks we are tracing */ 343 wakeup_reset(tr); 344 } 345 } 346 347 static void wakeup_tracer_ctrl_update(struct trace_array *tr) 348 { 349 if (tr->ctrl) 350 start_wakeup_tracer(tr); 351 else 352 stop_wakeup_tracer(tr); 353 } 354 355 static void wakeup_tracer_open(struct trace_iterator *iter) 356 { 357 /* stop the trace while dumping */ 358 if (iter->tr->ctrl) 359 stop_wakeup_tracer(iter->tr); 360 } 361 362 static void wakeup_tracer_close(struct trace_iterator *iter) 363 { 364 /* forget about any processes we were recording */ 365 if (iter->tr->ctrl) 366 start_wakeup_tracer(iter->tr); 367 } 368 369 static struct tracer wakeup_tracer __read_mostly = 370 { 371 .name = "wakeup", 372 .init = wakeup_tracer_init, 373 .reset = wakeup_tracer_reset, 374 .open = wakeup_tracer_open, 375 .close = wakeup_tracer_close, 376 .ctrl_update = wakeup_tracer_ctrl_update, 377 .print_max = 1, 378 #ifdef CONFIG_FTRACE_SELFTEST 379 .selftest = trace_selftest_startup_wakeup, 380 #endif 381 }; 382 383 __init static int init_wakeup_tracer(void) 384 { 385 int ret; 386 387 ret = register_tracer(&wakeup_tracer); 388 if (ret) 389 return ret; 390 391 return 0; 392 } 393 device_initcall(init_wakeup_tracer); 394