kernel/profile.c

   1 /*
   2  *  linux/kernel/profile.c
   3  *  Simple profiling. Manages a direct-mapped profile hit count buffer,
   4  *  with configurable resolution, support for restricting the cpus on
   5  *  which profiling is done, and switching between cpu time and
   6  *  schedule() calls via kernel command line parameters passed at boot.
   7  *
   8  *  Scheduler profiling support, Arjan van de Ven and Ingo Molnar,
   9  *      Red Hat, July 2004
  10  *  Consolidation of architecture support code for profiling,
  11  *      William Irwin, Oracle, July 2004
  12  *  Amortized hit count accounting via per-cpu open-addressed hashtables
  13  *      to resolve timer interrupt livelocks, William Irwin, Oracle, 2004
  14  */
  15
  16 #include <linux/module.h>
  17 #include <linux/profile.h>
  18 #include <linux/bootmem.h>
  19 #include <linux/notifier.h>
  20 #include <linux/mm.h>
  21 #include <linux/cpumask.h>
  22 #include <linux/cpu.h>
  23 #include <linux/highmem.h>
  24 #include <linux/mutex.h>
  25 #include <linux/slab.h>
  26 #include <linux/vmalloc.h>
  27 #include <asm/sections.h>
  28 #include <asm/irq_regs.h>
  29 #include <asm/ptrace.h>
  30
  31 struct profile_hit {
  32         u32 pc, hits;
  33 };
  34 #define PROFILE_GRPSHIFT        3
  35 #define PROFILE_GRPSZ           (1 << PROFILE_GRPSHIFT)
  36 #define NR_PROFILE_HIT          (PAGE_SIZE/sizeof(struct profile_hit))
  37 #define NR_PROFILE_GRP          (NR_PROFILE_HIT/PROFILE_GRPSZ)
  38
  39 /* Oprofile timer tick hook */
  40 static int (*timer_hook)(struct pt_regs *) __read_mostly;
  41
  42 static atomic_t *prof_buffer;
  43 static unsigned long prof_len, prof_shift;
  44
  45 int prof_on __read_mostly;
  46 EXPORT_SYMBOL_GPL(prof_on);
  47
  48 static cpumask_var_t prof_cpu_mask;
  49 #ifdef CONFIG_SMP
  50 static DEFINE_PER_CPU(struct profile_hit *[2], cpu_profile_hits);
  51 static DEFINE_PER_CPU(int, cpu_profile_flip);
  52 static DEFINE_MUTEX(profile_flip_mutex);
  53 #endif /* CONFIG_SMP */
  54
  55 int profile_setup(char *str)
  56 {
  57         static char schedstr[] = "schedule";
  58         static char sleepstr[] = "sleep";
  59         static char kvmstr[] = "kvm";
  60         int par;
  61
  62         if (!strncmp(str, sleepstr, strlen(sleepstr))) {
  63 #ifdef CONFIG_SCHEDSTATS
  64                 prof_on = SLEEP_PROFILING;
  65                 if (str[strlen(sleepstr)] == ',')
  66                         str += strlen(sleepstr) + 1;
  67                 if (get_option(&str, &par))
  68                         prof_shift = par;
  69                 printk(KERN_INFO
  70                         "kernel sleep profiling enabled (shift: %ld)\n",
  71                         prof_shift);
  72 #else
  73                 printk(KERN_WARNING
  74                         "kernel sleep profiling requires CONFIG_SCHEDSTATS\n");
  75 #endif /* CONFIG_SCHEDSTATS */
  76         } else if (!strncmp(str, schedstr, strlen(schedstr))) {
  77                 prof_on = SCHED_PROFILING;
  78                 if (str[strlen(schedstr)] == ',')
  79                         str += strlen(schedstr) + 1;
  80                 if (get_option(&str, &par))
  81                         prof_shift = par;
  82                 printk(KERN_INFO
  83                         "kernel schedule profiling enabled (shift: %ld)\n",
  84                         prof_shift);
  85         } else if (!strncmp(str, kvmstr, strlen(kvmstr))) {
  86                 prof_on = KVM_PROFILING;
  87                 if (str[strlen(kvmstr)] == ',')
  88                         str += strlen(kvmstr) + 1;
  89                 if (get_option(&str, &par))
  90                         prof_shift = par;
  91                 printk(KERN_INFO
  92                         "kernel KVM profiling enabled (shift: %ld)\n",
  93                         prof_shift);
  94         } else if (get_option(&str, &par)) {
  95                 prof_shift = par;
  96                 prof_on = CPU_PROFILING;
  97                 printk(KERN_INFO "kernel profiling enabled (shift: %ld)\n",
  98                         prof_shift);
  99         }
 100         return 1;
 101 }
 102 __setup("profile=", profile_setup);
 103
 104
 105 int __ref profile_init(void)
 106 {
 107         int buffer_bytes;
 108         if (!prof_on)
 109                 return 0;
 110
 111         /* only text is profiled */
 112         prof_len = (_etext - _stext) >> prof_shift;
 113         buffer_bytes = prof_len*sizeof(atomic_t);
 114
 115         if (!alloc_cpumask_var(&prof_cpu_mask, GFP_KERNEL))
 116                 return -ENOMEM;
 117
 118         cpumask_copy(prof_cpu_mask, cpu_possible_mask);
 119
 120         prof_buffer = kzalloc(buffer_bytes, GFP_KERNEL|__GFP_NOWARN);
 121         if (prof_buffer)
 122                 return 0;
 123
 124         prof_buffer = alloc_pages_exact(buffer_bytes,
 125                                         GFP_KERNEL|__GFP_ZERO|__GFP_NOWARN);
 126         if (prof_buffer)
 127                 return 0;
 128
 129         prof_buffer = vmalloc(buffer_bytes);
 130         if (prof_buffer)
 131                 return 0;
 132
 133         free_cpumask_var(prof_cpu_mask);
 134         return -ENOMEM;
 135 }
 136
 137 /* Profile event notifications */
 138
 139 static BLOCKING_NOTIFIER_HEAD(task_exit_notifier);
 140 static ATOMIC_NOTIFIER_HEAD(task_free_notifier);
 141 static BLOCKING_NOTIFIER_HEAD(munmap_notifier);
 142
 143 void profile_task_exit(struct task_struct *task)
 144 {
 145         blocking_notifier_call_chain(&task_exit_notifier, 0, task);
 146 }
 147
 148 int profile_handoff_task(struct task_struct *task)
 149 {
 150         int ret;
 151         ret = atomic_notifier_call_chain(&task_free_notifier, 0, task);
 152         return (ret == NOTIFY_OK) ? 1 : 0;
 153 }
 154
 155 void profile_munmap(unsigned long addr)
 156 {
 157         blocking_notifier_call_chain(&munmap_notifier, 0, (void *)addr);
 158 }
 159
 160 int task_handoff_register(struct notifier_block *n)
 161 {
 162         return atomic_notifier_chain_register(&task_free_notifier, n);
 163 }
 164 EXPORT_SYMBOL_GPL(task_handoff_register);
 165
 166 int task_handoff_unregister(struct notifier_block *n)
 167 {
 168         return atomic_notifier_chain_unregister(&task_free_notifier, n);
 169 }
 170 EXPORT_SYMBOL_GPL(task_handoff_unregister);
 171
 172 int profile_event_register(enum profile_type type, struct notifier_block *n)
 173 {
 174         int err = -EINVAL;
 175
 176         switch (type) {
 177         case PROFILE_TASK_EXIT:
 178                 err = blocking_notifier_chain_register(
 179                                 &task_exit_notifier, n);
 180                 break;
 181         case PROFILE_MUNMAP:
 182                 err = blocking_notifier_chain_register(
 183                                 &munmap_notifier, n);
 184                 break;
 185         }
 186
 187         return err;
 188 }
 189 EXPORT_SYMBOL_GPL(profile_event_register);
 190
 191 int profile_event_unregister(enum profile_type type, struct notifier_block *n)
 192 {
 193         int err = -EINVAL;
 194
 195         switch (type) {
 196         case PROFILE_TASK_EXIT:
 197                 err = blocking_notifier_chain_unregister(
 198                                 &task_exit_notifier, n);
 199                 break;
 200         case PROFILE_MUNMAP:
 201                 err = blocking_notifier_chain_unregister(
 202                                 &munmap_notifier, n);
 203                 break;
 204         }
 205
 206         return err;
 207 }
 208 EXPORT_SYMBOL_GPL(profile_event_unregister);
 209
 210 int register_timer_hook(int (*hook)(struct pt_regs *))
 211 {
 212         if (timer_hook)
 213                 return -EBUSY;
 214         timer_hook = hook;
 215         return 0;
 216 }
 217 EXPORT_SYMBOL_GPL(register_timer_hook);
 218
 219 void unregister_timer_hook(int (*hook)(struct pt_regs *))
 220 {
 221         WARN_ON(hook != timer_hook);
 222         timer_hook = NULL;
 223         /* make sure all CPUs see the NULL hook */
 224         synchronize_sched();  /* Allow ongoing interrupts to complete. */
 225 }
 226 EXPORT_SYMBOL_GPL(unregister_timer_hook);
 227
 228
 229 #ifdef CONFIG_SMP
 230 /*
 231  * Each cpu has a pair of open-addressed hashtables for pending
 232  * profile hits. read_profile() IPI's all cpus to request them
 233  * to flip buffers and flushes their contents to prof_buffer itself.
 234  * Flip requests are serialized by the profile_flip_mutex. The sole
 235  * use of having a second hashtable is for avoiding cacheline
 236  * contention that would otherwise happen during flushes of pending
 237  * profile hits required for the accuracy of reported profile hits
 238  * and so resurrect the interrupt livelock issue.
 239  *
 240  * The open-addressed hashtables are indexed by profile buffer slot
 241  * and hold the number of pending hits to that profile buffer slot on
 242  * a cpu in an entry. When the hashtable overflows, all pending hits
 243  * are accounted to their corresponding profile buffer slots with
 244  * atomic_add() and the hashtable emptied. As numerous pending hits
 245  * may be accounted to a profile buffer slot in a hashtable entry,
 246  * this amortizes a number of atomic profile buffer increments likely
 247  * to be far larger than the number of entries in the hashtable,
 248  * particularly given that the number of distinct profile buffer
 249  * positions to which hits are accounted during short intervals (e.g.
 250  * several seconds) is usually very small. Exclusion from buffer
 251  * flipping is provided by interrupt disablement (note that for
 252  * SCHED_PROFILING or SLEEP_PROFILING profile_hit() may be called from
 253  * process context).
 254  * The hash function is meant to be lightweight as opposed to strong,
 255  * and was vaguely inspired by ppc64 firmware-supported inverted
 256  * pagetable hash functions, but uses a full hashtable full of finite
 257  * collision chains, not just pairs of them.
 258  *
 259  * -- wli
 260  */
 261 static void __profile_flip_buffers(void *unused)
 262 {
 263         int cpu = smp_processor_id();
 264
 265         per_cpu(cpu_profile_flip, cpu) = !per_cpu(cpu_profile_flip, cpu);
 266 }
 267
 268 static void profile_flip_buffers(void)
 269 {
 270         int i, j, cpu;
 271
 272         mutex_lock(&profile_flip_mutex);
 273         j = per_cpu(cpu_profile_flip, get_cpu());
 274         put_cpu();
 275         on_each_cpu(__profile_flip_buffers, NULL, 1);
 276         for_each_online_cpu(cpu) {
 277                 struct profile_hit *hits = per_cpu(cpu_profile_hits, cpu)[j];
 278                 for (i = 0; i < NR_PROFILE_HIT; ++i) {
 279                         if (!hits[i].hits) {
 280                                 if (hits[i].pc)
 281                                         hits[i].pc = 0;
 282                                 continue;
 283                         }
 284                         atomic_add(hits[i].hits, &prof_buffer[hits[i].pc]);
 285                         hits[i].hits = hits[i].pc = 0;
 286                 }
 287         }
 288         mutex_unlock(&profile_flip_mutex);
 289 }
 290
 291 static void profile_discard_flip_buffers(void)
 292 {
 293         int i, cpu;
 294
 295         mutex_lock(&profile_flip_mutex);
 296         i = per_cpu(cpu_profile_flip, get_cpu());
 297         put_cpu();
 298         on_each_cpu(__profile_flip_buffers, NULL, 1);
 299         for_each_online_cpu(cpu) {
 300                 struct profile_hit *hits = per_cpu(cpu_profile_hits, cpu)[i];
 301                 memset(hits, 0, NR_PROFILE_HIT*sizeof(struct profile_hit));
 302         }
 303         mutex_unlock(&profile_flip_mutex);
 304 }
 305
 306 void profile_hits(int type, void *__pc, unsigned int nr_hits)
 307 {
 308         unsigned long primary, secondary, flags, pc = (unsigned long)__pc;
 309         int i, j, cpu;
 310         struct profile_hit *hits;
 311
 312         if (prof_on != type || !prof_buffer)
 313                 return;
 314         pc = min((pc - (unsigned long)_stext) >> prof_shift, prof_len - 1);
 315         i = primary = (pc & (NR_PROFILE_GRP - 1)) << PROFILE_GRPSHIFT;
 316         secondary = (~(pc << 1) & (NR_PROFILE_GRP - 1)) << PROFILE_GRPSHIFT;
 317         cpu = get_cpu();
 318         hits = per_cpu(cpu_profile_hits, cpu)[per_cpu(cpu_profile_flip, cpu)];
 319         if (!hits) {
 320                 put_cpu();
 321                 return;
 322         }
 323         /*
 324          * We buffer the global profiler buffer into a per-CPU
 325          * queue and thus reduce the number of global (and possibly
 326          * NUMA-alien) accesses. The write-queue is self-coalescing:
 327          */
 328         local_irq_save(flags);
 329         do {
 330                 for (j = 0; j < PROFILE_GRPSZ; ++j) {
 331                         if (hits[i + j].pc == pc) {
 332                                 hits[i + j].hits += nr_hits;
 333                                 goto out;
 334                         } else if (!hits[i + j].hits) {
 335                                 hits[i + j].pc = pc;
 336                                 hits[i + j].hits = nr_hits;
 337                                 goto out;
 338                         }
 339                 }
 340                 i = (i + secondary) & (NR_PROFILE_HIT - 1);
 341         } while (i != primary);
 342
 343         /*
 344          * Add the current hit(s) and flush the write-queue out
 345          * to the global buffer:
 346          */
 347         atomic_add(nr_hits, &prof_buffer[pc]);
 348         for (i = 0; i < NR_PROFILE_HIT; ++i) {
 349                 atomic_add(hits[i].hits, &prof_buffer[hits[i].pc]);
 350                 hits[i].pc = hits[i].hits = 0;
 351         }
 352 out:
 353         local_irq_restore(flags);
 354         put_cpu();
 355 }
 356
 357 static int __cpuinit profile_cpu_callback(struct notifier_block *info,
 358                                         unsigned long action, void *__cpu)
 359 {
 360         int node, cpu = (unsigned long)__cpu;
 361         struct page *page;
 362
 363         switch (action) {
 364         case CPU_UP_PREPARE:
 365         case CPU_UP_PREPARE_FROZEN:
 366                 node = cpu_to_node(cpu);
 367                 per_cpu(cpu_profile_flip, cpu) = 0;
 368                 if (!per_cpu(cpu_profile_hits, cpu)[1]) {
 369                         page = alloc_pages_exact_node(node,
 370                                         GFP_KERNEL | __GFP_ZERO,
 371                                         0);
 372                         if (!page)
 373                                 return NOTIFY_BAD;
 374                         per_cpu(cpu_profile_hits, cpu)[1] = page_address(page);
 375                 }
 376                 if (!per_cpu(cpu_profile_hits, cpu)[0]) {
 377                         page = alloc_pages_exact_node(node,
 378                                         GFP_KERNEL | __GFP_ZERO,
 379                                         0);
 380                         if (!page)
 381                                 goto out_free;
 382                         per_cpu(cpu_profile_hits, cpu)[0] = page_address(page);
 383                 }
 384                 break;
 385 out_free:
 386                 page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[1]);
 387                 per_cpu(cpu_profile_hits, cpu)[1] = NULL;
 388                 __free_page(page);
 389                 return NOTIFY_BAD;
 390         case CPU_ONLINE:
 391         case CPU_ONLINE_FROZEN:
 392                 if (prof_cpu_mask != NULL)
 393                         cpumask_set_cpu(cpu, prof_cpu_mask);
 394                 break;
 395         case CPU_UP_CANCELED:
 396         case CPU_UP_CANCELED_FROZEN:
 397         case CPU_DEAD:
 398         case CPU_DEAD_FROZEN:
 399                 if (prof_cpu_mask != NULL)
 400                         cpumask_clear_cpu(cpu, prof_cpu_mask);
 401                 if (per_cpu(cpu_profile_hits, cpu)[0]) {
 402                         page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[0]);
 403                         per_cpu(cpu_profile_hits, cpu)[0] = NULL;
 404                         __free_page(page);
 405                 }
 406                 if (per_cpu(cpu_profile_hits, cpu)[1]) {
 407                         page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[1]);
 408                         per_cpu(cpu_profile_hits, cpu)[1] = NULL;
 409                         __free_page(page);
 410                 }
 411                 break;
 412         }
 413         return NOTIFY_OK;
 414 }
 415 #else /* !CONFIG_SMP */
 416 #define profile_flip_buffers()          do { } while (0)
 417 #define profile_discard_flip_buffers()  do { } while (0)
 418 #define profile_cpu_callback            NULL
 419
 420 void profile_hits(int type, void *__pc, unsigned int nr_hits)
 421 {
 422         unsigned long pc;
 423
 424         if (prof_on != type || !prof_buffer)
 425                 return;
 426         pc = ((unsigned long)__pc - (unsigned long)_stext) >> prof_shift;
 427         atomic_add(nr_hits, &prof_buffer[min(pc, prof_len - 1)]);
 428 }
 429 #endif /* !CONFIG_SMP */
 430 EXPORT_SYMBOL_GPL(profile_hits);
 431
 432 void profile_tick(int type)
 433 {
 434         struct pt_regs *regs = get_irq_regs();
 435
 436         if (type == CPU_PROFILING && timer_hook)
 437                 timer_hook(regs);
 438         if (!user_mode(regs) && prof_cpu_mask != NULL &&
 439             cpumask_test_cpu(smp_processor_id(), prof_cpu_mask))
 440                 profile_hit(type, (void *)profile_pc(regs));
 441 }
 442
 443 #ifdef CONFIG_PROC_FS
 444 #include <linux/proc_fs.h>
 445 #include <asm/uaccess.h>
 446
 447 static int prof_cpu_mask_read_proc(char *page, char **start, off_t off,
 448                         int count, int *eof, void *data)
 449 {
 450         int len = cpumask_scnprintf(page, count, data);
 451         if (count - len < 2)
 452                 return -EINVAL;
 453         len += sprintf(page + len, "\n");
 454         return len;
 455 }
 456
 457 static int prof_cpu_mask_write_proc(struct file *file,
 458         const char __user *buffer,  unsigned long count, void *data)
 459 {
 460         struct cpumask *mask = data;
 461         unsigned long full_count = count, err;
 462         cpumask_var_t new_value;
 463
 464         if (!alloc_cpumask_var(&new_value, GFP_KERNEL))
 465                 return -ENOMEM;
 466
 467         err = cpumask_parse_user(buffer, count, new_value);
 468         if (!err) {
 469                 cpumask_copy(mask, new_value);
 470                 err = full_count;
 471         }
 472         free_cpumask_var(new_value);
 473         return err;
 474 }
 475
 476 void create_prof_cpu_mask(struct proc_dir_entry *root_irq_dir)
 477 {
 478         struct proc_dir_entry *entry;
 479
 480         /* create /proc/irq/prof_cpu_mask */
 481         entry = create_proc_entry("prof_cpu_mask", 0600, root_irq_dir);
 482         if (!entry)
 483                 return;
 484         entry->data = prof_cpu_mask;
 485         entry->read_proc = prof_cpu_mask_read_proc;
 486         entry->write_proc = prof_cpu_mask_write_proc;
 487 }
 488
 489 /*
 490  * This function accesses profiling information. The returned data is
 491  * binary: the sampling step and the actual contents of the profile
 492  * buffer. Use of the program readprofile is recommended in order to
 493  * get meaningful info out of these data.
 494  */
 495 static ssize_t
 496 read_profile(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 497 {
 498         unsigned long p = *ppos;
 499         ssize_t read;
 500         char *pnt;
 501         unsigned int sample_step = 1 << prof_shift;
 502
 503         profile_flip_buffers();
 504         if (p >= (prof_len+1)*sizeof(unsigned int))
 505                 return 0;
 506         if (count > (prof_len+1)*sizeof(unsigned int) - p)
 507                 count = (prof_len+1)*sizeof(unsigned int) - p;
 508         read = 0;
 509
 510         while (p < sizeof(unsigned int) && count > 0) {
 511                 if (put_user(*((char *)(&sample_step)+p), buf))
 512                         return -EFAULT;
 513                 buf++; p++; count--; read++;
 514         }
 515         pnt = (char *)prof_buffer + p - sizeof(atomic_t);
 516         if (copy_to_user(buf, (void *)pnt, count))
 517                 return -EFAULT;
 518         read += count;
 519         *ppos += read;
 520         return read;
 521 }
 522
 523 /*
 524  * Writing to /proc/profile resets the counters
 525  *
 526  * Writing a 'profiling multiplier' value into it also re-sets the profiling
 527  * interrupt frequency, on architectures that support this.
 528  */
 529 static ssize_t write_profile(struct file *file, const char __user *buf,
 530                              size_t count, loff_t *ppos)
 531 {
 532 #ifdef CONFIG_SMP
 533         extern int setup_profiling_timer(unsigned int multiplier);
 534
 535         if (count == sizeof(int)) {
 536                 unsigned int multiplier;
 537
 538                 if (copy_from_user(&multiplier, buf, sizeof(int)))
 539                         return -EFAULT;
 540
 541                 if (setup_profiling_timer(multiplier))
 542                         return -EINVAL;
 543         }
 544 #endif
 545         profile_discard_flip_buffers();
 546         memset(prof_buffer, 0, prof_len * sizeof(atomic_t));
 547         return count;
 548 }
 549
 550 static const struct file_operations proc_profile_operations = {
 551         .read           = read_profile,
 552         .write          = write_profile,
 553 };
 554
 555 #ifdef CONFIG_SMP
 556 static void profile_nop(void *unused)
 557 {
 558 }
 559
 560 static int create_hash_tables(void)
 561 {
 562         int cpu;
 563
 564         for_each_online_cpu(cpu) {
 565                 int node = cpu_to_node(cpu);
 566                 struct page *page;
 567
 568                 page = alloc_pages_exact_node(node,
 569                                 GFP_KERNEL | __GFP_ZERO | GFP_THISNODE,
 570                                 0);
 571                 if (!page)
 572                         goto out_cleanup;
 573                 per_cpu(cpu_profile_hits, cpu)[1]
 574                                 = (struct profile_hit *)page_address(page);
 575                 page = alloc_pages_exact_node(node,
 576                                 GFP_KERNEL | __GFP_ZERO | GFP_THISNODE,
 577                                 0);
 578                 if (!page)
 579                         goto out_cleanup;
 580                 per_cpu(cpu_profile_hits, cpu)[0]
 581                                 = (struct profile_hit *)page_address(page);
 582         }
 583         return 0;
 584 out_cleanup:
 585         prof_on = 0;
 586         smp_mb();
 587         on_each_cpu(profile_nop, NULL, 1);
 588         for_each_online_cpu(cpu) {
 589                 struct page *page;
 590
 591                 if (per_cpu(cpu_profile_hits, cpu)[0]) {
 592                         page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[0]);
 593                         per_cpu(cpu_profile_hits, cpu)[0] = NULL;
 594                         __free_page(page);
 595                 }
 596                 if (per_cpu(cpu_profile_hits, cpu)[1]) {
 597                         page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[1]);
 598                         per_cpu(cpu_profile_hits, cpu)[1] = NULL;
 599                         __free_page(page);
 600                 }
 601         }
 602         return -1;
 603 }
 604 #else
 605 #define create_hash_tables()                    ({ 0; })
 606 #endif
 607
 608 int __ref create_proc_profile(void) /* false positive from hotcpu_notifier */
 609 {
 610         struct proc_dir_entry *entry;
 611
 612         if (!prof_on)
 613                 return 0;
 614         if (create_hash_tables())
 615                 return -ENOMEM;
 616         entry = proc_create("profile", S_IWUSR | S_IRUGO,
 617                             NULL, &proc_profile_operations);
 618         if (!entry)
 619                 return 0;
 620         entry->size = (1+prof_len) * sizeof(atomic_t);
 621         hotcpu_notifier(profile_cpu_callback, 0);
 622         return 0;
 623 }
 624 module_init(create_proc_profile);
 625 #endif /* CONFIG_PROC_FS */