kernel/trace/trace_irqsoff.c

   1 /*
   2  * trace irqs off critical timings
   3  *
   4  * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
   5  * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
   6  *
   7  * From code in 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/kallsyms.h>
  13 #include <linux/debugfs.h>
  14 #include <linux/uaccess.h>
  15 #include <linux/module.h>
  16 #include <linux/ftrace.h>
  17 #include <linux/fs.h>
  18
  19 #include "trace.h"
  20
  21 static struct trace_array               *irqsoff_trace __read_mostly;
  22 static int                              tracer_enabled __read_mostly;
  23
  24 static DEFINE_PER_CPU(int, tracing_cpu);
  25
  26 static DEFINE_SPINLOCK(max_trace_lock);
  27
  28 enum {
  29         TRACER_IRQS_OFF         = (1 << 1),
  30         TRACER_PREEMPT_OFF      = (1 << 2),
  31 };
  32
  33 static int trace_type __read_mostly;
  34
  35 static int save_lat_flag;
  36
  37 static void stop_irqsoff_tracer(struct trace_array *tr, int graph);
  38 static int start_irqsoff_tracer(struct trace_array *tr, int graph);
  39
  40 #ifdef CONFIG_PREEMPT_TRACER
  41 static inline int
  42 preempt_trace(void)
  43 {
  44         return ((trace_type & TRACER_PREEMPT_OFF) && preempt_count());
  45 }
  46 #else
  47 # define preempt_trace() (0)
  48 #endif
  49
  50 #ifdef CONFIG_IRQSOFF_TRACER
  51 static inline int
  52 irq_trace(void)
  53 {
  54         return ((trace_type & TRACER_IRQS_OFF) &&
  55                 irqs_disabled());
  56 }
  57 #else
  58 # define irq_trace() (0)
  59 #endif
  60
  61 #define TRACE_DISPLAY_GRAPH     1
  62
  63 static struct tracer_opt trace_opts[] = {
  64 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
  65         /* display latency trace as call graph */
  66         { TRACER_OPT(display-graph, TRACE_DISPLAY_GRAPH) },
  67 #endif
  68         { } /* Empty entry */
  69 };
  70
  71 static struct tracer_flags tracer_flags = {
  72         .val  = 0,
  73         .opts = trace_opts,
  74 };
  75
  76 #define is_graph() (tracer_flags.val & TRACE_DISPLAY_GRAPH)
  77
  78 /*
  79  * Sequence count - we record it when starting a measurement and
  80  * skip the latency if the sequence has changed - some other section
  81  * did a maximum and could disturb our measurement with serial console
  82  * printouts, etc. Truly coinciding maximum latencies should be rare
  83  * and what happens together happens separately as well, so this doesnt
  84  * decrease the validity of the maximum found:
  85  */
  86 static __cacheline_aligned_in_smp       unsigned long max_sequence;
  87
  88 #ifdef CONFIG_FUNCTION_TRACER
  89 /*
  90  * irqsoff uses its own tracer function to keep the overhead down:
  91  */
  92 static void
  93 irqsoff_tracer_call(unsigned long ip, unsigned long parent_ip)
  94 {
  95         struct trace_array *tr = irqsoff_trace;
  96         struct trace_array_cpu *data;
  97         unsigned long flags;
  98         long disabled;
  99         int cpu;
 100
 101         /*
 102          * Does not matter if we preempt. We test the flags
 103          * afterward, to see if irqs are disabled or not.
 104          * If we preempt and get a false positive, the flags
 105          * test will fail.
 106          */
 107         cpu = raw_smp_processor_id();
 108         if (likely(!per_cpu(tracing_cpu, cpu)))
 109                 return;
 110
 111         local_save_flags(flags);
 112         /* slight chance to get a false positive on tracing_cpu */
 113         if (!irqs_disabled_flags(flags))
 114                 return;
 115
 116         data = tr->data[cpu];
 117         disabled = atomic_inc_return(&data->disabled);
 118
 119         if (likely(disabled == 1))
 120                 trace_function(tr, ip, parent_ip, flags, preempt_count());
 121
 122         atomic_dec(&data->disabled);
 123 }
 124
 125 static struct ftrace_ops trace_ops __read_mostly =
 126 {
 127         .func = irqsoff_tracer_call,
 128 };
 129 #endif /* CONFIG_FUNCTION_TRACER */
 130
 131 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 132 static int irqsoff_set_flag(u32 old_flags, u32 bit, int set)
 133 {
 134         int cpu;
 135
 136         if (!(bit & TRACE_DISPLAY_GRAPH))
 137                 return -EINVAL;
 138
 139         if (!(is_graph() ^ set))
 140                 return 0;
 141
 142         stop_irqsoff_tracer(irqsoff_trace, !set);
 143
 144         for_each_possible_cpu(cpu)
 145                 per_cpu(tracing_cpu, cpu) = 0;
 146
 147         tracing_max_latency = 0;
 148         tracing_reset_online_cpus(irqsoff_trace);
 149
 150         return start_irqsoff_tracer(irqsoff_trace, set);
 151 }
 152
 153 static int irqsoff_graph_entry(struct ftrace_graph_ent *trace)
 154 {
 155         struct trace_array *tr = irqsoff_trace;
 156         struct trace_array_cpu *data;
 157         unsigned long flags;
 158         long disabled;
 159         int ret;
 160         int cpu;
 161         int pc;
 162
 163         cpu = raw_smp_processor_id();
 164         if (likely(!per_cpu(tracing_cpu, cpu)))
 165                 return 0;
 166
 167         local_save_flags(flags);
 168         /* slight chance to get a false positive on tracing_cpu */
 169         if (!irqs_disabled_flags(flags))
 170                 return 0;
 171
 172         data = tr->data[cpu];
 173         disabled = atomic_inc_return(&data->disabled);
 174
 175         if (likely(disabled == 1)) {
 176                 pc = preempt_count();
 177                 ret = __trace_graph_entry(tr, trace, flags, pc);
 178         } else
 179                 ret = 0;
 180
 181         atomic_dec(&data->disabled);
 182         return ret;
 183 }
 184
 185 static void irqsoff_graph_return(struct ftrace_graph_ret *trace)
 186 {
 187         struct trace_array *tr = irqsoff_trace;
 188         struct trace_array_cpu *data;
 189         unsigned long flags;
 190         long disabled;
 191         int cpu;
 192         int pc;
 193
 194         cpu = raw_smp_processor_id();
 195         if (likely(!per_cpu(tracing_cpu, cpu)))
 196                 return;
 197
 198         local_save_flags(flags);
 199         /* slight chance to get a false positive on tracing_cpu */
 200         if (!irqs_disabled_flags(flags))
 201                 return;
 202
 203         data = tr->data[cpu];
 204         disabled = atomic_inc_return(&data->disabled);
 205
 206         if (likely(disabled == 1)) {
 207                 pc = preempt_count();
 208                 __trace_graph_return(tr, trace, flags, pc);
 209         }
 210
 211         atomic_dec(&data->disabled);
 212 }
 213
 214 static void irqsoff_trace_open(struct trace_iterator *iter)
 215 {
 216         if (is_graph())
 217                 graph_trace_open(iter);
 218
 219 }
 220
 221 static void irqsoff_trace_close(struct trace_iterator *iter)
 222 {
 223         if (iter->private)
 224                 graph_trace_close(iter);
 225 }
 226
 227 #define GRAPH_TRACER_FLAGS (TRACE_GRAPH_PRINT_CPU | \
 228                             TRACE_GRAPH_PRINT_PROC)
 229
 230 static enum print_line_t irqsoff_print_line(struct trace_iterator *iter)
 231 {
 232         u32 flags = GRAPH_TRACER_FLAGS;
 233
 234         if (trace_flags & TRACE_ITER_LATENCY_FMT)
 235                 flags |= TRACE_GRAPH_PRINT_DURATION;
 236         else
 237                 flags |= TRACE_GRAPH_PRINT_ABS_TIME;
 238
 239         /*
 240          * In graph mode call the graph tracer output function,
 241          * otherwise go with the TRACE_FN event handler
 242          */
 243         if (is_graph())
 244                 return print_graph_function_flags(iter, flags);
 245
 246         return TRACE_TYPE_UNHANDLED;
 247 }
 248
 249 static void irqsoff_print_header(struct seq_file *s)
 250 {
 251         if (is_graph()) {
 252                 struct trace_iterator *iter = s->private;
 253                 u32 flags = GRAPH_TRACER_FLAGS;
 254
 255                 if (trace_flags & TRACE_ITER_LATENCY_FMT) {
 256                         /* print nothing if the buffers are empty */
 257                         if (trace_empty(iter))
 258                                 return;
 259
 260                         print_trace_header(s, iter);
 261                         flags |= TRACE_GRAPH_PRINT_DURATION;
 262                 } else
 263                         flags |= TRACE_GRAPH_PRINT_ABS_TIME;
 264
 265                 print_graph_headers_flags(s, flags);
 266         } else
 267                 trace_default_header(s);
 268 }
 269
 270 static void
 271 trace_graph_function(struct trace_array *tr,
 272                  unsigned long ip, unsigned long flags, int pc)
 273 {
 274         u64 time = trace_clock_local();
 275         struct ftrace_graph_ent ent = {
 276                 .func  = ip,
 277                 .depth = 0,
 278         };
 279         struct ftrace_graph_ret ret = {
 280                 .func     = ip,
 281                 .depth    = 0,
 282                 .calltime = time,
 283                 .rettime  = time,
 284         };
 285
 286         __trace_graph_entry(tr, &ent, flags, pc);
 287         __trace_graph_return(tr, &ret, flags, pc);
 288 }
 289
 290 static void
 291 __trace_function(struct trace_array *tr,
 292                  unsigned long ip, unsigned long parent_ip,
 293                  unsigned long flags, int pc)
 294 {
 295         if (!is_graph())
 296                 trace_function(tr, ip, parent_ip, flags, pc);
 297         else {
 298                 trace_graph_function(tr, parent_ip, flags, pc);
 299                 trace_graph_function(tr, ip, flags, pc);
 300         }
 301 }
 302
 303 #else
 304 #define __trace_function trace_function
 305
 306 static int irqsoff_set_flag(u32 old_flags, u32 bit, int set)
 307 {
 308         return -EINVAL;
 309 }
 310
 311 static int irqsoff_graph_entry(struct ftrace_graph_ent *trace)
 312 {
 313         return -1;
 314 }
 315
 316 static enum print_line_t irqsoff_print_line(struct trace_iterator *iter)
 317 {
 318         return TRACE_TYPE_UNHANDLED;
 319 }
 320
 321 static void irqsoff_graph_return(struct ftrace_graph_ret *trace) { }
 322 static void irqsoff_print_header(struct seq_file *s) { }
 323 static void irqsoff_trace_open(struct trace_iterator *iter) { }
 324 static void irqsoff_trace_close(struct trace_iterator *iter) { }
 325 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 326
 327 /*
 328  * Should this new latency be reported/recorded?
 329  */
 330 static int report_latency(cycle_t delta)
 331 {
 332         if (tracing_thresh) {
 333                 if (delta < tracing_thresh)
 334                         return 0;
 335         } else {
 336                 if (delta <= tracing_max_latency)
 337                         return 0;
 338         }
 339         return 1;
 340 }
 341
 342 static void
 343 check_critical_timing(struct trace_array *tr,
 344                       struct trace_array_cpu *data,
 345                       unsigned long parent_ip,
 346                       int cpu)
 347 {
 348         cycle_t T0, T1, delta;
 349         unsigned long flags;
 350         int pc;
 351
 352         T0 = data->preempt_timestamp;
 353         T1 = ftrace_now(cpu);
 354         delta = T1-T0;
 355
 356         local_save_flags(flags);
 357
 358         pc = preempt_count();
 359
 360         if (!report_latency(delta))
 361                 goto out;
 362
 363         spin_lock_irqsave(&max_trace_lock, flags);
 364
 365         /* check if we are still the max latency */
 366         if (!report_latency(delta))
 367                 goto out_unlock;
 368
 369         __trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
 370         /* Skip 5 functions to get to the irq/preempt enable function */
 371         __trace_stack(tr, flags, 5, pc);
 372
 373         if (data->critical_sequence != max_sequence)
 374                 goto out_unlock;
 375
 376         data->critical_end = parent_ip;
 377
 378         if (likely(!is_tracing_stopped())) {
 379                 tracing_max_latency = delta;
 380                 update_max_tr_single(tr, current, cpu);
 381         }
 382
 383         max_sequence++;
 384
 385 out_unlock:
 386         spin_unlock_irqrestore(&max_trace_lock, flags);
 387
 388 out:
 389         data->critical_sequence = max_sequence;
 390         data->preempt_timestamp = ftrace_now(cpu);
 391         __trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
 392 }
 393
 394 static inline void
 395 start_critical_timing(unsigned long ip, unsigned long parent_ip)
 396 {
 397         int cpu;
 398         struct trace_array *tr = irqsoff_trace;
 399         struct trace_array_cpu *data;
 400         unsigned long flags;
 401
 402         if (likely(!tracer_enabled))
 403                 return;
 404
 405         cpu = raw_smp_processor_id();
 406
 407         if (per_cpu(tracing_cpu, cpu))
 408                 return;
 409
 410         data = tr->data[cpu];
 411
 412         if (unlikely(!data) || atomic_read(&data->disabled))
 413                 return;
 414
 415         atomic_inc(&data->disabled);
 416
 417         data->critical_sequence = max_sequence;
 418         data->preempt_timestamp = ftrace_now(cpu);
 419         data->critical_start = parent_ip ? : ip;
 420
 421         local_save_flags(flags);
 422
 423         __trace_function(tr, ip, parent_ip, flags, preempt_count());
 424
 425         per_cpu(tracing_cpu, cpu) = 1;
 426
 427         atomic_dec(&data->disabled);
 428 }
 429
 430 static inline void
 431 stop_critical_timing(unsigned long ip, unsigned long parent_ip)
 432 {
 433         int cpu;
 434         struct trace_array *tr = irqsoff_trace;
 435         struct trace_array_cpu *data;
 436         unsigned long flags;
 437
 438         cpu = raw_smp_processor_id();
 439         /* Always clear the tracing cpu on stopping the trace */
 440         if (unlikely(per_cpu(tracing_cpu, cpu)))
 441                 per_cpu(tracing_cpu, cpu) = 0;
 442         else
 443                 return;
 444
 445         if (!tracer_enabled)
 446                 return;
 447
 448         data = tr->data[cpu];
 449
 450         if (unlikely(!data) ||
 451             !data->critical_start || atomic_read(&data->disabled))
 452                 return;
 453
 454         atomic_inc(&data->disabled);
 455
 456         local_save_flags(flags);
 457         __trace_function(tr, ip, parent_ip, flags, preempt_count());
 458         check_critical_timing(tr, data, parent_ip ? : ip, cpu);
 459         data->critical_start = 0;
 460         atomic_dec(&data->disabled);
 461 }
 462
 463 /* start and stop critical timings used to for stoppage (in idle) */
 464 void start_critical_timings(void)
 465 {
 466         if (preempt_trace() || irq_trace())
 467                 start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
 468 }
 469 EXPORT_SYMBOL_GPL(start_critical_timings);
 470
 471 void stop_critical_timings(void)
 472 {
 473         if (preempt_trace() || irq_trace())
 474                 stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
 475 }
 476 EXPORT_SYMBOL_GPL(stop_critical_timings);
 477
 478 #ifdef CONFIG_IRQSOFF_TRACER
 479 #ifdef CONFIG_PROVE_LOCKING
 480 void time_hardirqs_on(unsigned long a0, unsigned long a1)
 481 {
 482         if (!preempt_trace() && irq_trace())
 483                 stop_critical_timing(a0, a1);
 484 }
 485
 486 void time_hardirqs_off(unsigned long a0, unsigned long a1)
 487 {
 488         if (!preempt_trace() && irq_trace())
 489                 start_critical_timing(a0, a1);
 490 }
 491
 492 #else /* !CONFIG_PROVE_LOCKING */
 493
 494 /*
 495  * Stubs:
 496  */
 497
 498 void early_boot_irqs_off(void)
 499 {
 500 }
 501
 502 void early_boot_irqs_on(void)
 503 {
 504 }
 505
 506 void trace_softirqs_on(unsigned long ip)
 507 {
 508 }
 509
 510 void trace_softirqs_off(unsigned long ip)
 511 {
 512 }
 513
 514 inline void print_irqtrace_events(struct task_struct *curr)
 515 {
 516 }
 517
 518 /*
 519  * We are only interested in hardirq on/off events:
 520  */
 521 void trace_hardirqs_on(void)
 522 {
 523         if (!preempt_trace() && irq_trace())
 524                 stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
 525 }
 526 EXPORT_SYMBOL(trace_hardirqs_on);
 527
 528 void trace_hardirqs_off(void)
 529 {
 530         if (!preempt_trace() && irq_trace())
 531                 start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
 532 }
 533 EXPORT_SYMBOL(trace_hardirqs_off);
 534
 535 void trace_hardirqs_on_caller(unsigned long caller_addr)
 536 {
 537         if (!preempt_trace() && irq_trace())
 538                 stop_critical_timing(CALLER_ADDR0, caller_addr);
 539 }
 540 EXPORT_SYMBOL(trace_hardirqs_on_caller);
 541
 542 void trace_hardirqs_off_caller(unsigned long caller_addr)
 543 {
 544         if (!preempt_trace() && irq_trace())
 545                 start_critical_timing(CALLER_ADDR0, caller_addr);
 546 }
 547 EXPORT_SYMBOL(trace_hardirqs_off_caller);
 548
 549 #endif /* CONFIG_PROVE_LOCKING */
 550 #endif /*  CONFIG_IRQSOFF_TRACER */
 551
 552 #ifdef CONFIG_PREEMPT_TRACER
 553 void trace_preempt_on(unsigned long a0, unsigned long a1)
 554 {
 555         if (preempt_trace())
 556                 stop_critical_timing(a0, a1);
 557 }
 558
 559 void trace_preempt_off(unsigned long a0, unsigned long a1)
 560 {
 561         if (preempt_trace())
 562                 start_critical_timing(a0, a1);
 563 }
 564 #endif /* CONFIG_PREEMPT_TRACER */
 565
 566 static int start_irqsoff_tracer(struct trace_array *tr, int graph)
 567 {
 568         int ret = 0;
 569
 570         if (!graph)
 571                 ret = register_ftrace_function(&trace_ops);
 572         else
 573                 ret = register_ftrace_graph(&irqsoff_graph_return,
 574                                             &irqsoff_graph_entry);
 575
 576         if (!ret && tracing_is_enabled())
 577                 tracer_enabled = 1;
 578         else
 579                 tracer_enabled = 0;
 580
 581         return ret;
 582 }
 583
 584 static void stop_irqsoff_tracer(struct trace_array *tr, int graph)
 585 {
 586         tracer_enabled = 0;
 587
 588         if (!graph)
 589                 unregister_ftrace_function(&trace_ops);
 590         else
 591                 unregister_ftrace_graph();
 592 }
 593
 594 static void __irqsoff_tracer_init(struct trace_array *tr)
 595 {
 596         save_lat_flag = trace_flags & TRACE_ITER_LATENCY_FMT;
 597         trace_flags |= TRACE_ITER_LATENCY_FMT;
 598
 599         tracing_max_latency = 0;
 600         irqsoff_trace = tr;
 601         /* make sure that the tracer is visible */
 602         smp_wmb();
 603         tracing_reset_online_cpus(tr);
 604
 605         if (start_irqsoff_tracer(tr, is_graph()))
 606                 printk(KERN_ERR "failed to start irqsoff tracer\n");
 607 }
 608
 609 static void irqsoff_tracer_reset(struct trace_array *tr)
 610 {
 611         stop_irqsoff_tracer(tr, is_graph());
 612
 613         if (!save_lat_flag)
 614                 trace_flags &= ~TRACE_ITER_LATENCY_FMT;
 615 }
 616
 617 static void irqsoff_tracer_start(struct trace_array *tr)
 618 {
 619         tracer_enabled = 1;
 620 }
 621
 622 static void irqsoff_tracer_stop(struct trace_array *tr)
 623 {
 624         tracer_enabled = 0;
 625 }
 626
 627 #ifdef CONFIG_IRQSOFF_TRACER
 628 static int irqsoff_tracer_init(struct trace_array *tr)
 629 {
 630         trace_type = TRACER_IRQS_OFF;
 631
 632         __irqsoff_tracer_init(tr);
 633         return 0;
 634 }
 635 static struct tracer irqsoff_tracer __read_mostly =
 636 {
 637         .name           = "irqsoff",
 638         .init           = irqsoff_tracer_init,
 639         .reset          = irqsoff_tracer_reset,
 640         .start          = irqsoff_tracer_start,
 641         .stop           = irqsoff_tracer_stop,
 642         .print_max      = 1,
 643         .print_header   = irqsoff_print_header,
 644         .print_line     = irqsoff_print_line,
 645         .flags          = &tracer_flags,
 646         .set_flag       = irqsoff_set_flag,
 647 #ifdef CONFIG_FTRACE_SELFTEST
 648         .selftest    = trace_selftest_startup_irqsoff,
 649 #endif
 650         .open           = irqsoff_trace_open,
 651         .close          = irqsoff_trace_close,
 652 };
 653 # define register_irqsoff(trace) register_tracer(&trace)
 654 #else
 655 # define register_irqsoff(trace) do { } while (0)
 656 #endif
 657
 658 #ifdef CONFIG_PREEMPT_TRACER
 659 static int preemptoff_tracer_init(struct trace_array *tr)
 660 {
 661         trace_type = TRACER_PREEMPT_OFF;
 662
 663         __irqsoff_tracer_init(tr);
 664         return 0;
 665 }
 666
 667 static struct tracer preemptoff_tracer __read_mostly =
 668 {
 669         .name           = "preemptoff",
 670         .init           = preemptoff_tracer_init,
 671         .reset          = irqsoff_tracer_reset,
 672         .start          = irqsoff_tracer_start,
 673         .stop           = irqsoff_tracer_stop,
 674         .print_max      = 1,
 675         .print_header   = irqsoff_print_header,
 676         .print_line     = irqsoff_print_line,
 677         .flags          = &tracer_flags,
 678         .set_flag       = irqsoff_set_flag,
 679 #ifdef CONFIG_FTRACE_SELFTEST
 680         .selftest    = trace_selftest_startup_preemptoff,
 681 #endif
 682         .open           = irqsoff_trace_open,
 683         .close          = irqsoff_trace_close,
 684 };
 685 # define register_preemptoff(trace) register_tracer(&trace)
 686 #else
 687 # define register_preemptoff(trace) do { } while (0)
 688 #endif
 689
 690 #if defined(CONFIG_IRQSOFF_TRACER) && \
 691         defined(CONFIG_PREEMPT_TRACER)
 692
 693 static int preemptirqsoff_tracer_init(struct trace_array *tr)
 694 {
 695         trace_type = TRACER_IRQS_OFF | TRACER_PREEMPT_OFF;
 696
 697         __irqsoff_tracer_init(tr);
 698         return 0;
 699 }
 700
 701 static struct tracer preemptirqsoff_tracer __read_mostly =
 702 {
 703         .name           = "preemptirqsoff",
 704         .init           = preemptirqsoff_tracer_init,
 705         .reset          = irqsoff_tracer_reset,
 706         .start          = irqsoff_tracer_start,
 707         .stop           = irqsoff_tracer_stop,
 708         .print_max      = 1,
 709         .print_header   = irqsoff_print_header,
 710         .print_line     = irqsoff_print_line,
 711         .flags          = &tracer_flags,
 712         .set_flag       = irqsoff_set_flag,
 713 #ifdef CONFIG_FTRACE_SELFTEST
 714         .selftest    = trace_selftest_startup_preemptirqsoff,
 715 #endif
 716         .open           = irqsoff_trace_open,
 717         .close          = irqsoff_trace_close,
 718 };
 719
 720 # define register_preemptirqsoff(trace) register_tracer(&trace)
 721 #else
 722 # define register_preemptirqsoff(trace) do { } while (0)
 723 #endif
 724
 725 __init static int init_irqsoff_tracer(void)
 726 {
 727         register_irqsoff(irqsoff_tracer);
 728         register_preemptoff(preemptoff_tracer);
 729         register_preemptirqsoff(preemptirqsoff_tracer);
 730
 731         return 0;
 732 }
 733 device_initcall(init_irqsoff_tracer);