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                 memset(prof_buffer, 0, buffer_bytes);
 132                 return 0;
 133         }
 134
 135         free_cpumask_var(prof_cpu_mask);
 136         return -ENOMEM;
 137 }
 138
 139 /* Profile event notifications */
 140
 141 static BLOCKING_NOTIFIER_HEAD(task_exit_notifier);
 142 static ATOMIC_NOTIFIER_HEAD(task_free_notifier);
 143 static BLOCKING_NOTIFIER_HEAD(munmap_notifier);
 144
 145 void profile_task_exit(struct task_struct *task)
 146 {
 147         blocking_notifier_call_chain(&task_exit_notifier, 0, task);
 148 }
 149
 150 int profile_handoff_task(struct task_struct *task)
 151 {
 152         int ret;
 153         ret = atomic_notifier_call_chain(&task_free_notifier, 0, task);
 154         return (ret == NOTIFY_OK) ? 1 : 0;
 155 }
 156
 157 void profile_munmap(unsigned long addr)
 158 {
 159         blocking_notifier_call_chain(&munmap_notifier, 0, (void *)addr);
 160 }
 161
 162 int task_handoff_register(struct notifier_block *n)
 163 {
 164         return atomic_notifier_chain_register(&task_free_notifier, n);
 165 }
 166 EXPORT_SYMBOL_GPL(task_handoff_register);
 167
 168 int task_handoff_unregister(struct notifier_block *n)
 169 {
 170         return atomic_notifier_chain_unregister(&task_free_notifier, n);
 171 }
 172 EXPORT_SYMBOL_GPL(task_handoff_unregister);
 173
 174 int profile_event_register(enum profile_type type, struct notifier_block *n)
 175 {
 176         int err = -EINVAL;
 177
 178         switch (type) {
 179         case PROFILE_TASK_EXIT:
 180                 err = blocking_notifier_chain_register(
 181                                 &task_exit_notifier, n);
 182                 break;
 183         case PROFILE_MUNMAP:
 184                 err = blocking_notifier_chain_register(
 185                                 &munmap_notifier, n);
 186                 break;
 187         }
 188
 189         return err;
 190 }
 191 EXPORT_SYMBOL_GPL(profile_event_register);
 192
 193 int profile_event_unregister(enum profile_type type, struct notifier_block *n)
 194 {
 195         int err = -EINVAL;
 196
 197         switch (type) {
 198         case PROFILE_TASK_EXIT:
 199                 err = blocking_notifier_chain_unregister(
 200                                 &task_exit_notifier, n);
 201                 break;
 202         case PROFILE_MUNMAP:
 203                 err = blocking_notifier_chain_unregister(
 204                                 &munmap_notifier, n);
 205                 break;
 206         }
 207
 208         return err;
 209 }
 210 EXPORT_SYMBOL_GPL(profile_event_unregister);
 211
 212 int register_timer_hook(int (*hook)(struct pt_regs *))
 213 {
 214         if (timer_hook)
 215                 return -EBUSY;
 216         timer_hook = hook;
 217         return 0;
 218 }
 219 EXPORT_SYMBOL_GPL(register_timer_hook);
 220
 221 void unregister_timer_hook(int (*hook)(struct pt_regs *))
 222 {
 223         WARN_ON(hook != timer_hook);
 224         timer_hook = NULL;
 225         /* make sure all CPUs see the NULL hook */
 226         synchronize_sched();  /* Allow ongoing interrupts to complete. */
 227 }
 228 EXPORT_SYMBOL_GPL(unregister_timer_hook);
 229
 230
 231 #ifdef CONFIG_SMP
 232 /*
 233  * Each cpu has a pair of open-addressed hashtables for pending
 234  * profile hits. read_profile() IPI's all cpus to request them
 235  * to flip buffers and flushes their contents to prof_buffer itself.
 236  * Flip requests are serialized by the profile_flip_mutex. The sole
 237  * use of having a second hashtable is for avoiding cacheline
 238  * contention that would otherwise happen during flushes of pending
 239  * profile hits required for the accuracy of reported profile hits
 240  * and so resurrect the interrupt livelock issue.
 241  *
 242  * The open-addressed hashtables are indexed by profile buffer slot
 243  * and hold the number of pending hits to that profile buffer slot on
 244  * a cpu in an entry. When the hashtable overflows, all pending hits
 245  * are accounted to their corresponding profile buffer slots with
 246  * atomic_add() and the hashtable emptied. As numerous pending hits
 247  * may be accounted to a profile buffer slot in a hashtable entry,
 248  * this amortizes a number of atomic profile buffer increments likely
 249  * to be far larger than the number of entries in the hashtable,
 250  * particularly given that the number of distinct profile buffer
 251  * positions to which hits are accounted during short intervals (e.g.
 252  * several seconds) is usually very small. Exclusion from buffer
 253  * flipping is provided by interrupt disablement (note that for
 254  * SCHED_PROFILING or SLEEP_PROFILING profile_hit() may be called from
 255  * process context).
 256  * The hash function is meant to be lightweight as opposed to strong,
 257  * and was vaguely inspired by ppc64 firmware-supported inverted
 258  * pagetable hash functions, but uses a full hashtable full of finite
 259  * collision chains, not just pairs of them.
 260  *
 261  * -- wli
 262  */
 263 static void __profile_flip_buffers(void *unused)
 264 {
 265         int cpu = smp_processor_id();
 266
 267         per_cpu(cpu_profile_flip, cpu) = !per_cpu(cpu_profile_flip, cpu);
 268 }
 269
 270 static void profile_flip_buffers(void)
 271 {
 272         int i, j, cpu;
 273
 274         mutex_lock(&profile_flip_mutex);
 275         j = per_cpu(cpu_profile_flip, get_cpu());
 276         put_cpu();
 277         on_each_cpu(__profile_flip_buffers, NULL, 1);
 278         for_each_online_cpu(cpu) {
 279                 struct profile_hit *hits = per_cpu(cpu_profile_hits, cpu)[j];
 280                 for (i = 0; i < NR_PROFILE_HIT; ++i) {
 281                         if (!hits[i].hits) {
 282                                 if (hits[i].pc)
 283                                         hits[i].pc = 0;
 284                                 continue;
 285                         }
 286                         atomic_add(hits[i].hits, &prof_buffer[hits[i].pc]);
 287                         hits[i].hits = hits[i].pc = 0;
 288                 }
 289         }
 290         mutex_unlock(&profile_flip_mutex);
 291 }
 292
 293 static void profile_discard_flip_buffers(void)
 294 {
 295         int i, cpu;
 296
 297         mutex_lock(&profile_flip_mutex);
 298         i = per_cpu(cpu_profile_flip, get_cpu());
 299         put_cpu();
 300         on_each_cpu(__profile_flip_buffers, NULL, 1);
 301         for_each_online_cpu(cpu) {
 302                 struct profile_hit *hits = per_cpu(cpu_profile_hits, cpu)[i];
 303                 memset(hits, 0, NR_PROFILE_HIT*sizeof(struct profile_hit));
 304         }
 305         mutex_unlock(&profile_flip_mutex);
 306 }
 307
 308 void profile_hits(int type, void *__pc, unsigned int nr_hits)
 309 {
 310         unsigned long primary, secondary, flags, pc = (unsigned long)__pc;
 311         int i, j, cpu;
 312         struct profile_hit *hits;
 313
 314         if (prof_on != type || !prof_buffer)
 315                 return;
 316         pc = min((pc - (unsigned long)_stext) >> prof_shift, prof_len - 1);
 317         i = primary = (pc & (NR_PROFILE_GRP - 1)) << PROFILE_GRPSHIFT;
 318         secondary = (~(pc << 1) & (NR_PROFILE_GRP - 1)) << PROFILE_GRPSHIFT;
 319         cpu = get_cpu();
 320         hits = per_cpu(cpu_profile_hits, cpu)[per_cpu(cpu_profile_flip, cpu)];
 321         if (!hits) {
 322                 put_cpu();
 323                 return;
 324         }
 325         /*
 326          * We buffer the global profiler buffer into a per-CPU
 327          * queue and thus reduce the number of global (and possibly
 328          * NUMA-alien) accesses. The write-queue is self-coalescing:
 329          */
 330         local_irq_save(flags);
 331         do {
 332                 for (j = 0; j < PROFILE_GRPSZ; ++j) {
 333                         if (hits[i + j].pc == pc) {
 334                                 hits[i + j].hits += nr_hits;
 335                                 goto out;
 336                         } else if (!hits[i + j].hits) {
 337                                 hits[i + j].pc = pc;
 338                                 hits[i + j].hits = nr_hits;
 339                                 goto out;
 340                         }
 341                 }
 342                 i = (i + secondary) & (NR_PROFILE_HIT - 1);
 343         } while (i != primary);
 344
 345         /*
 346          * Add the current hit(s) and flush the write-queue out
 347          * to the global buffer:
 348          */
 349         atomic_add(nr_hits, &prof_buffer[pc]);
 350         for (i = 0; i < NR_PROFILE_HIT; ++i) {
 351                 atomic_add(hits[i].hits, &prof_buffer[hits[i].pc]);
 352                 hits[i].pc = hits[i].hits = 0;
 353         }
 354 out:
 355         local_irq_restore(flags);
 356         put_cpu();
 357 }
 358
 359 static int __cpuinit profile_cpu_callback(struct notifier_block *info,
 360                                         unsigned long action, void *__cpu)
 361 {
 362         int node, cpu = (unsigned long)__cpu;
 363         struct page *page;
 364
 365         switch (action) {
 366         case CPU_UP_PREPARE:
 367         case CPU_UP_PREPARE_FROZEN:
 368                 node = cpu_to_mem(cpu);
 369                 per_cpu(cpu_profile_flip, cpu) = 0;
 370                 if (!per_cpu(cpu_profile_hits, cpu)[1]) {
 371                         page = alloc_pages_exact_node(node,
 372                                         GFP_KERNEL | __GFP_ZERO,
 373                                         0);
 374                         if (!page)
 375                                 return notifier_from_errno(-ENOMEM);
 376                         per_cpu(cpu_profile_hits, cpu)[1] = page_address(page);
 377                 }
 378                 if (!per_cpu(cpu_profile_hits, cpu)[0]) {
 379                         page = alloc_pages_exact_node(node,
 380                                         GFP_KERNEL | __GFP_ZERO,
 381                                         0);
 382                         if (!page)
 383                                 goto out_free;
 384                         per_cpu(cpu_profile_hits, cpu)[0] = page_address(page);
 385                 }
 386                 break;
 387 out_free:
 388                 page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[1]);
 389                 per_cpu(cpu_profile_hits, cpu)[1] = NULL;
 390                 __free_page(page);
 391                 return notifier_from_errno(-ENOMEM);
 392         case CPU_ONLINE:
 393         case CPU_ONLINE_FROZEN:
 394                 if (prof_cpu_mask != NULL)
 395                         cpumask_set_cpu(cpu, prof_cpu_mask);
 396                 break;
 397         case CPU_UP_CANCELED:
 398         case CPU_UP_CANCELED_FROZEN:
 399         case CPU_DEAD:
 400         case CPU_DEAD_FROZEN:
 401                 if (prof_cpu_mask != NULL)
 402                         cpumask_clear_cpu(cpu, prof_cpu_mask);
 403                 if (per_cpu(cpu_profile_hits, cpu)[0]) {
 404                         page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[0]);
 405                         per_cpu(cpu_profile_hits, cpu)[0] = NULL;
 406                         __free_page(page);
 407                 }
 408                 if (per_cpu(cpu_profile_hits, cpu)[1]) {
 409                         page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[1]);
 410                         per_cpu(cpu_profile_hits, cpu)[1] = NULL;
 411                         __free_page(page);
 412                 }
 413                 break;
 414         }
 415         return NOTIFY_OK;
 416 }
 417 #else /* !CONFIG_SMP */
 418 #define profile_flip_buffers()          do { } while (0)
 419 #define profile_discard_flip_buffers()  do { } while (0)
 420 #define profile_cpu_callback            NULL
 421
 422 void profile_hits(int type, void *__pc, unsigned int nr_hits)
 423 {
 424         unsigned long pc;
 425
 426         if (prof_on != type || !prof_buffer)
 427                 return;
 428         pc = ((unsigned long)__pc - (unsigned long)_stext) >> prof_shift;
 429         atomic_add(nr_hits, &prof_buffer[min(pc, prof_len - 1)]);
 430 }
 431 #endif /* !CONFIG_SMP */
 432 EXPORT_SYMBOL_GPL(profile_hits);
 433
 434 void profile_tick(int type)
 435 {
 436         struct pt_regs *regs = get_irq_regs();
 437
 438         if (type == CPU_PROFILING && timer_hook)
 439                 timer_hook(regs);
 440         if (!user_mode(regs) && prof_cpu_mask != NULL &&
 441             cpumask_test_cpu(smp_processor_id(), prof_cpu_mask))
 442                 profile_hit(type, (void *)profile_pc(regs));
 443 }
 444
 445 #ifdef CONFIG_PROC_FS
 446 #include <linux/proc_fs.h>
 447 #include <linux/seq_file.h>
 448 #include <asm/uaccess.h>
 449
 450 static int prof_cpu_mask_proc_show(struct seq_file *m, void *v)
 451 {
 452         seq_cpumask(m, prof_cpu_mask);
 453         seq_putc(m, '\n');
 454         return 0;
 455 }
 456
 457 static int prof_cpu_mask_proc_open(struct inode *inode, struct file *file)
 458 {
 459         return single_open(file, prof_cpu_mask_proc_show, NULL);
 460 }
 461
 462 static ssize_t prof_cpu_mask_proc_write(struct file *file,
 463         const char __user *buffer, size_t count, loff_t *pos)
 464 {
 465         cpumask_var_t new_value;
 466         int err;
 467
 468         if (!alloc_cpumask_var(&new_value, GFP_KERNEL))
 469                 return -ENOMEM;
 470
 471         err = cpumask_parse_user(buffer, count, new_value);
 472         if (!err) {
 473                 cpumask_copy(prof_cpu_mask, new_value);
 474                 err = count;
 475         }
 476         free_cpumask_var(new_value);
 477         return err;
 478 }
 479
 480 static const struct file_operations prof_cpu_mask_proc_fops = {
 481         .open           = prof_cpu_mask_proc_open,
 482         .read           = seq_read,
 483         .llseek         = seq_lseek,
 484         .release        = single_release,
 485         .write          = prof_cpu_mask_proc_write,
 486 };
 487
 488 void create_prof_cpu_mask(struct proc_dir_entry *root_irq_dir)
 489 {
 490         /* create /proc/irq/prof_cpu_mask */
 491         proc_create("prof_cpu_mask", 0600, root_irq_dir, &prof_cpu_mask_proc_fops);
 492 }
 493
 494 /*
 495  * This function accesses profiling information. The returned data is
 496  * binary: the sampling step and the actual contents of the profile
 497  * buffer. Use of the program readprofile is recommended in order to
 498  * get meaningful info out of these data.
 499  */
 500 static ssize_t
 501 read_profile(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 502 {
 503         unsigned long p = *ppos;
 504         ssize_t read;
 505         char *pnt;
 506         unsigned int sample_step = 1 << prof_shift;
 507
 508         profile_flip_buffers();
 509         if (p >= (prof_len+1)*sizeof(unsigned int))
 510                 return 0;
 511         if (count > (prof_len+1)*sizeof(unsigned int) - p)
 512                 count = (prof_len+1)*sizeof(unsigned int) - p;
 513         read = 0;
 514
 515         while (p < sizeof(unsigned int) && count > 0) {
 516                 if (put_user(*((char *)(&sample_step)+p), buf))
 517                         return -EFAULT;
 518                 buf++; p++; count--; read++;
 519         }
 520         pnt = (char *)prof_buffer + p - sizeof(atomic_t);
 521         if (copy_to_user(buf, (void *)pnt, count))
 522                 return -EFAULT;
 523         read += count;
 524         *ppos += read;
 525         return read;
 526 }
 527
 528 /*
 529  * Writing to /proc/profile resets the counters
 530  *
 531  * Writing a 'profiling multiplier' value into it also re-sets the profiling
 532  * interrupt frequency, on architectures that support this.
 533  */
 534 static ssize_t write_profile(struct file *file, const char __user *buf,
 535                              size_t count, loff_t *ppos)
 536 {
 537 #ifdef CONFIG_SMP
 538         extern int setup_profiling_timer(unsigned int multiplier);
 539
 540         if (count == sizeof(int)) {
 541                 unsigned int multiplier;
 542
 543                 if (copy_from_user(&multiplier, buf, sizeof(int)))
 544                         return -EFAULT;
 545
 546                 if (setup_profiling_timer(multiplier))
 547                         return -EINVAL;
 548         }
 549 #endif
 550         profile_discard_flip_buffers();
 551         memset(prof_buffer, 0, prof_len * sizeof(atomic_t));
 552         return count;
 553 }
 554
 555 static const struct file_operations proc_profile_operations = {
 556         .read           = read_profile,
 557         .write          = write_profile,
 558         .llseek         = default_llseek,
 559 };
 560
 561 #ifdef CONFIG_SMP
 562 static void profile_nop(void *unused)
 563 {
 564 }
 565
 566 static int create_hash_tables(void)
 567 {
 568         int cpu;
 569
 570         for_each_online_cpu(cpu) {
 571                 int node = cpu_to_mem(cpu);
 572                 struct page *page;
 573
 574                 page = alloc_pages_exact_node(node,
 575                                 GFP_KERNEL | __GFP_ZERO | GFP_THISNODE,
 576                                 0);
 577                 if (!page)
 578                         goto out_cleanup;
 579                 per_cpu(cpu_profile_hits, cpu)[1]
 580                                 = (struct profile_hit *)page_address(page);
 581                 page = alloc_pages_exact_node(node,
 582                                 GFP_KERNEL | __GFP_ZERO | GFP_THISNODE,
 583                                 0);
 584                 if (!page)
 585                         goto out_cleanup;
 586                 per_cpu(cpu_profile_hits, cpu)[0]
 587                                 = (struct profile_hit *)page_address(page);
 588         }
 589         return 0;
 590 out_cleanup:
 591         prof_on = 0;
 592         smp_mb();
 593         on_each_cpu(profile_nop, NULL, 1);
 594         for_each_online_cpu(cpu) {
 595                 struct page *page;
 596
 597                 if (per_cpu(cpu_profile_hits, cpu)[0]) {
 598                         page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[0]);
 599                         per_cpu(cpu_profile_hits, cpu)[0] = NULL;
 600                         __free_page(page);
 601                 }
 602                 if (per_cpu(cpu_profile_hits, cpu)[1]) {
 603                         page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[1]);
 604                         per_cpu(cpu_profile_hits, cpu)[1] = NULL;
 605                         __free_page(page);
 606                 }
 607         }
 608         return -1;
 609 }
 610 #else
 611 #define create_hash_tables()                    ({ 0; })
 612 #endif
 613
 614 int __ref create_proc_profile(void) /* false positive from hotcpu_notifier */
 615 {
 616         struct proc_dir_entry *entry;
 617
 618         if (!prof_on)
 619                 return 0;
 620         if (create_hash_tables())
 621                 return -ENOMEM;
 622         entry = proc_create("profile", S_IWUSR | S_IRUGO,
 623                             NULL, &proc_profile_operations);
 624         if (!entry)
 625                 return 0;
 626         entry->size = (1+prof_len) * sizeof(atomic_t);
 627         hotcpu_notifier(profile_cpu_callback, 0);
 628         return 0;
 629 }
 630 module_init(create_proc_profile);
 631 #endif /* CONFIG_PROC_FS */