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 = ftrace_preempt_disable(); 54 55 cpu = raw_smp_processor_id(); 56 data = tr->data[cpu]; 57 disabled = atomic_inc_return(&data->disabled); 58 if (unlikely(disabled != 1)) 59 goto out; 60 61 local_irq_save(flags); 62 __raw_spin_lock(&wakeup_lock); 63 64 if (unlikely(!wakeup_task)) 65 goto unlock; 66 67 /* 68 * The task can't disappear because it needs to 69 * wake up first, and we have the wakeup_lock. 70 */ 71 if (task_cpu(wakeup_task) != cpu) 72 goto unlock; 73 74 trace_function(tr, data, ip, parent_ip, flags, pc); 75 76 unlock: 77 __raw_spin_unlock(&wakeup_lock); 78 local_irq_restore(flags); 79 80 out: 81 atomic_dec(&data->disabled); 82 83 ftrace_preempt_enable(resched); 84 } 85 86 static struct ftrace_ops trace_ops __read_mostly = 87 { 88 .func = wakeup_tracer_call, 89 }; 90 #endif /* CONFIG_FUNCTION_TRACER */ 91 92 /* 93 * Should this new latency be reported/recorded? 94 */ 95 static int report_latency(cycle_t delta) 96 { 97 if (tracing_thresh) { 98 if (delta < tracing_thresh) 99 return 0; 100 } else { 101 if (delta <= tracing_max_latency) 102 return 0; 103 } 104 return 1; 105 } 106 107 static void notrace 108 probe_wakeup_sched_switch(struct rq *rq, struct task_struct *prev, 109 struct task_struct *next) 110 { 111 unsigned long latency = 0, t0 = 0, t1 = 0; 112 struct trace_array_cpu *data; 113 cycle_t T0, T1, delta; 114 unsigned long flags; 115 long disabled; 116 int cpu; 117 int pc; 118 119 tracing_record_cmdline(prev); 120 121 if (unlikely(!tracer_enabled)) 122 return; 123 124 /* 125 * When we start a new trace, we set wakeup_task to NULL 126 * and then set tracer_enabled = 1. We want to make sure 127 * that another CPU does not see the tracer_enabled = 1 128 * and the wakeup_task with an older task, that might 129 * actually be the same as next. 130 */ 131 smp_rmb(); 132 133 if (next != wakeup_task) 134 return; 135 136 pc = preempt_count(); 137 138 /* The task we are waiting for is waking up */ 139 data = wakeup_trace->data[wakeup_cpu]; 140 141 /* disable local data, not wakeup_cpu data */ 142 cpu = raw_smp_processor_id(); 143 disabled = atomic_inc_return(&wakeup_trace->data[cpu]->disabled); 144 if (likely(disabled != 1)) 145 goto out; 146 147 local_irq_save(flags); 148 __raw_spin_lock(&wakeup_lock); 149 150 /* We could race with grabbing wakeup_lock */ 151 if (unlikely(!tracer_enabled || next != wakeup_task)) 152 goto out_unlock; 153 154 trace_function(wakeup_trace, data, CALLER_ADDR1, CALLER_ADDR2, flags, pc); 155 156 /* 157 * usecs conversion is slow so we try to delay the conversion 158 * as long as possible: 159 */ 160 T0 = data->preempt_timestamp; 161 T1 = ftrace_now(cpu); 162 delta = T1-T0; 163 164 if (!report_latency(delta)) 165 goto out_unlock; 166 167 latency = nsecs_to_usecs(delta); 168 169 tracing_max_latency = delta; 170 t0 = nsecs_to_usecs(T0); 171 t1 = nsecs_to_usecs(T1); 172 173 update_max_tr(wakeup_trace, wakeup_task, wakeup_cpu); 174 175 out_unlock: 176 __wakeup_reset(wakeup_trace); 177 __raw_spin_unlock(&wakeup_lock); 178 local_irq_restore(flags); 179 out: 180 atomic_dec(&wakeup_trace->data[cpu]->disabled); 181 } 182 183 static void __wakeup_reset(struct trace_array *tr) 184 { 185 struct trace_array_cpu *data; 186 int cpu; 187 188 for_each_possible_cpu(cpu) { 189 data = tr->data[cpu]; 190 tracing_reset(tr, cpu); 191 } 192 193 wakeup_cpu = -1; 194 wakeup_prio = -1; 195 196 if (wakeup_task) 197 put_task_struct(wakeup_task); 198 199 wakeup_task = NULL; 200 } 201 202 static void wakeup_reset(struct trace_array *tr) 203 { 204 unsigned long flags; 205 206 local_irq_save(flags); 207 __raw_spin_lock(&wakeup_lock); 208 __wakeup_reset(tr); 209 __raw_spin_unlock(&wakeup_lock); 210 local_irq_restore(flags); 211 } 212 213 static void 214 probe_wakeup(struct rq *rq, struct task_struct *p, int success) 215 { 216 int cpu = smp_processor_id(); 217 unsigned long flags; 218 long disabled; 219 int pc; 220 221 if (likely(!tracer_enabled)) 222 return; 223 224 tracing_record_cmdline(p); 225 tracing_record_cmdline(current); 226 227 if (likely(!rt_task(p)) || 228 p->prio >= wakeup_prio || 229 p->prio >= current->prio) 230 return; 231 232 pc = preempt_count(); 233 disabled = atomic_inc_return(&wakeup_trace->data[cpu]->disabled); 234 if (unlikely(disabled != 1)) 235 goto out; 236 237 /* interrupts should be off from try_to_wake_up */ 238 __raw_spin_lock(&wakeup_lock); 239 240 /* check for races. */ 241 if (!tracer_enabled || p->prio >= wakeup_prio) 242 goto out_locked; 243 244 /* reset the trace */ 245 __wakeup_reset(wakeup_trace); 246 247 wakeup_cpu = task_cpu(p); 248 wakeup_prio = p->prio; 249 250 wakeup_task = p; 251 get_task_struct(wakeup_task); 252 253 local_save_flags(flags); 254 255 wakeup_trace->data[wakeup_cpu]->preempt_timestamp = ftrace_now(cpu); 256 trace_function(wakeup_trace, wakeup_trace->data[wakeup_cpu], 257 CALLER_ADDR1, CALLER_ADDR2, flags, pc); 258 259 out_locked: 260 __raw_spin_unlock(&wakeup_lock); 261 out: 262 atomic_dec(&wakeup_trace->data[cpu]->disabled); 263 } 264 265 /* 266 * save_tracer_enabled is used to save the state of the tracer_enabled 267 * variable when we disable it when we open a trace output file. 268 */ 269 static int save_tracer_enabled; 270 271 static void start_wakeup_tracer(struct trace_array *tr) 272 { 273 int ret; 274 275 ret = register_trace_sched_wakeup(probe_wakeup); 276 if (ret) { 277 pr_info("wakeup trace: Couldn't activate tracepoint" 278 " probe to kernel_sched_wakeup\n"); 279 return; 280 } 281 282 ret = register_trace_sched_wakeup_new(probe_wakeup); 283 if (ret) { 284 pr_info("wakeup trace: Couldn't activate tracepoint" 285 " probe to kernel_sched_wakeup_new\n"); 286 goto fail_deprobe; 287 } 288 289 ret = register_trace_sched_switch(probe_wakeup_sched_switch); 290 if (ret) { 291 pr_info("sched trace: Couldn't activate tracepoint" 292 " probe to kernel_sched_schedule\n"); 293 goto fail_deprobe_wake_new; 294 } 295 296 wakeup_reset(tr); 297 298 /* 299 * Don't let the tracer_enabled = 1 show up before 300 * the wakeup_task is reset. This may be overkill since 301 * wakeup_reset does a spin_unlock after setting the 302 * wakeup_task to NULL, but I want to be safe. 303 * This is a slow path anyway. 304 */ 305 smp_wmb(); 306 307 register_ftrace_function(&trace_ops); 308 309 if (tracing_is_enabled()) { 310 tracer_enabled = 1; 311 save_tracer_enabled = 1; 312 } else { 313 tracer_enabled = 0; 314 save_tracer_enabled = 0; 315 } 316 317 return; 318 fail_deprobe_wake_new: 319 unregister_trace_sched_wakeup_new(probe_wakeup); 320 fail_deprobe: 321 unregister_trace_sched_wakeup(probe_wakeup); 322 } 323 324 static void stop_wakeup_tracer(struct trace_array *tr) 325 { 326 tracer_enabled = 0; 327 save_tracer_enabled = 0; 328 unregister_ftrace_function(&trace_ops); 329 unregister_trace_sched_switch(probe_wakeup_sched_switch); 330 unregister_trace_sched_wakeup_new(probe_wakeup); 331 unregister_trace_sched_wakeup(probe_wakeup); 332 } 333 334 static int wakeup_tracer_init(struct trace_array *tr) 335 { 336 tracing_max_latency = 0; 337 wakeup_trace = tr; 338 start_wakeup_tracer(tr); 339 return 0; 340 } 341 342 static void wakeup_tracer_reset(struct trace_array *tr) 343 { 344 stop_wakeup_tracer(tr); 345 /* make sure we put back any tasks we are tracing */ 346 wakeup_reset(tr); 347 } 348 349 static void wakeup_tracer_start(struct trace_array *tr) 350 { 351 wakeup_reset(tr); 352 tracer_enabled = 1; 353 save_tracer_enabled = 1; 354 } 355 356 static void wakeup_tracer_stop(struct trace_array *tr) 357 { 358 tracer_enabled = 0; 359 save_tracer_enabled = 0; 360 } 361 362 static void wakeup_tracer_open(struct trace_iterator *iter) 363 { 364 /* stop the trace while dumping */ 365 tracer_enabled = 0; 366 } 367 368 static void wakeup_tracer_close(struct trace_iterator *iter) 369 { 370 /* forget about any processes we were recording */ 371 if (save_tracer_enabled) { 372 wakeup_reset(iter->tr); 373 tracer_enabled = 1; 374 } 375 } 376 377 static struct tracer wakeup_tracer __read_mostly = 378 { 379 .name = "wakeup", 380 .init = wakeup_tracer_init, 381 .reset = wakeup_tracer_reset, 382 .start = wakeup_tracer_start, 383 .stop = wakeup_tracer_stop, 384 .open = wakeup_tracer_open, 385 .close = wakeup_tracer_close, 386 .print_max = 1, 387 #ifdef CONFIG_FTRACE_SELFTEST 388 .selftest = trace_selftest_startup_wakeup, 389 #endif 390 }; 391 392 __init static int init_wakeup_tracer(void) 393 { 394 int ret; 395 396 ret = register_tracer(&wakeup_tracer); 397 if (ret) 398 return ret; 399 400 return 0; 401 } 402 device_initcall(init_wakeup_tracer); 403