kernel/time/timer_stats.c

   1 /*
   2  * kernel/time/timer_stats.c
   3  *
   4  * Collect timer usage statistics.
   5  *
   6  * Copyright(C) 2006, Red Hat, Inc., Ingo Molnar
   7  * Copyright(C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
   8  *
   9  * timer_stats is based on timer_top, a similar functionality which was part of
  10  * Con Kolivas dyntick patch set. It was developed by Daniel Petrini at the
  11  * Instituto Nokia de Tecnologia - INdT - Manaus. timer_top's design was based
  12  * on dynamic allocation of the statistics entries and linear search based
  13  * lookup combined with a global lock, rather than the static array, hash
  14  * and per-CPU locking which is used by timer_stats. It was written for the
  15  * pre hrtimer kernel code and therefore did not take hrtimers into account.
  16  * Nevertheless it provided the base for the timer_stats implementation and
  17  * was a helpful source of inspiration. Kudos to Daniel and the Nokia folks
  18  * for this effort.
  19  *
  20  * timer_top.c is
  21  *      Copyright (C) 2005 Instituto Nokia de Tecnologia - INdT - Manaus
  22  *      Written by Daniel Petrini <d.pensator@gmail.com>
  23  *      timer_top.c was released under the GNU General Public License version 2
  24  *
  25  * We export the addresses and counting of timer functions being called,
  26  * the pid and cmdline from the owner process if applicable.
  27  *
  28  * Start/stop data collection:
  29  * # echo 1[0] >/proc/timer_stats
  30  *
  31  * Display the information collected so far:
  32  * # cat /proc/timer_stats
  33  *
  34  * This program is free software; you can redistribute it and/or modify
  35  * it under the terms of the GNU General Public License version 2 as
  36  * published by the Free Software Foundation.
  37  */
  38
  39 #include <linux/proc_fs.h>
  40 #include <linux/module.h>
  41 #include <linux/spinlock.h>
  42 #include <linux/sched.h>
  43 #include <linux/seq_file.h>
  44 #include <linux/kallsyms.h>
  45
  46 #include <asm/uaccess.h>
  47
  48 /*
  49  * This is our basic unit of interest: a timer expiry event identified
  50  * by the timer, its start/expire functions and the PID of the task that
  51  * started the timer. We count the number of times an event happens:
  52  */
  53 struct entry {
  54         /*
  55          * Hash list:
  56          */
  57         struct entry            *next;
  58
  59         /*
  60          * Hash keys:
  61          */
  62         void                    *timer;
  63         void                    *start_func;
  64         void                    *expire_func;
  65         pid_t                   pid;
  66
  67         /*
  68          * Number of timeout events:
  69          */
  70         unsigned long           count;
  71
  72         /*
  73          * We save the command-line string to preserve
  74          * this information past task exit:
  75          */
  76         char                    comm[TASK_COMM_LEN + 1];
  77
  78 } ____cacheline_aligned_in_smp;
  79
  80 /*
  81  * Spinlock protecting the tables - not taken during lookup:
  82  */
  83 static DEFINE_SPINLOCK(table_lock);
  84
  85 /*
  86  * Per-CPU lookup locks for fast hash lookup:
  87  */
  88 static DEFINE_PER_CPU(spinlock_t, lookup_lock);
  89
  90 /*
  91  * Mutex to serialize state changes with show-stats activities:
  92  */
  93 static DEFINE_MUTEX(show_mutex);
  94
  95 /*
  96  * Collection status, active/inactive:
  97  */
  98 static int __read_mostly active;
  99
 100 /*
 101  * Beginning/end timestamps of measurement:
 102  */
 103 static ktime_t time_start, time_stop;
 104
 105 /*
 106  * tstat entry structs only get allocated while collection is
 107  * active and never freed during that time - this simplifies
 108  * things quite a bit.
 109  *
 110  * They get freed when a new collection period is started.
 111  */
 112 #define MAX_ENTRIES_BITS        10
 113 #define MAX_ENTRIES             (1UL << MAX_ENTRIES_BITS)
 114
 115 static unsigned long nr_entries;
 116 static struct entry entries[MAX_ENTRIES];
 117
 118 static atomic_t overflow_count;
 119
 120 /*
 121  * The entries are in a hash-table, for fast lookup:
 122  */
 123 #define TSTAT_HASH_BITS         (MAX_ENTRIES_BITS - 1)
 124 #define TSTAT_HASH_SIZE         (1UL << TSTAT_HASH_BITS)
 125 #define TSTAT_HASH_MASK         (TSTAT_HASH_SIZE - 1)
 126
 127 #define __tstat_hashfn(entry)                                           \
 128         (((unsigned long)(entry)->timer       ^                         \
 129           (unsigned long)(entry)->start_func  ^                         \
 130           (unsigned long)(entry)->expire_func ^                         \
 131           (unsigned long)(entry)->pid           ) & TSTAT_HASH_MASK)
 132
 133 #define tstat_hashentry(entry)  (tstat_hash_table + __tstat_hashfn(entry))
 134
 135 static struct entry *tstat_hash_table[TSTAT_HASH_SIZE] __read_mostly;
 136
 137 static void reset_entries(void)
 138 {
 139         nr_entries = 0;
 140         memset(entries, 0, sizeof(entries));
 141         memset(tstat_hash_table, 0, sizeof(tstat_hash_table));
 142         atomic_set(&overflow_count, 0);
 143 }
 144
 145 static struct entry *alloc_entry(void)
 146 {
 147         if (nr_entries >= MAX_ENTRIES)
 148                 return NULL;
 149
 150         return entries + nr_entries++;
 151 }
 152
 153 static int match_entries(struct entry *entry1, struct entry *entry2)
 154 {
 155         return entry1->timer       == entry2->timer       &&
 156                entry1->start_func  == entry2->start_func  &&
 157                entry1->expire_func == entry2->expire_func &&
 158                entry1->pid         == entry2->pid;
 159 }
 160
 161 /*
 162  * Look up whether an entry matching this item is present
 163  * in the hash already. Must be called with irqs off and the
 164  * lookup lock held:
 165  */
 166 static struct entry *tstat_lookup(struct entry *entry, char *comm)
 167 {
 168         struct entry **head, *curr, *prev;
 169
 170         head = tstat_hashentry(entry);
 171         curr = *head;
 172
 173         /*
 174          * The fastpath is when the entry is already hashed,
 175          * we do this with the lookup lock held, but with the
 176          * table lock not held:
 177          */
 178         while (curr) {
 179                 if (match_entries(curr, entry))
 180                         return curr;
 181
 182                 curr = curr->next;
 183         }
 184         /*
 185          * Slowpath: allocate, set up and link a new hash entry:
 186          */
 187         prev = NULL;
 188         curr = *head;
 189
 190         spin_lock(&table_lock);
 191         /*
 192          * Make sure we have not raced with another CPU:
 193          */
 194         while (curr) {
 195                 if (match_entries(curr, entry))
 196                         goto out_unlock;
 197
 198                 prev = curr;
 199                 curr = curr->next;
 200         }
 201
 202         curr = alloc_entry();
 203         if (curr) {
 204                 *curr = *entry;
 205                 curr->count = 0;
 206                 curr->next = NULL;
 207                 memcpy(curr->comm, comm, TASK_COMM_LEN);
 208
 209                 smp_mb(); /* Ensure that curr is initialized before insert */
 210
 211                 if (prev)
 212                         prev->next = curr;
 213                 else
 214                         *head = curr;
 215         }
 216  out_unlock:
 217         spin_unlock(&table_lock);
 218
 219         return curr;
 220 }
 221
 222 /**
 223  * timer_stats_update_stats - Update the statistics for a timer.
 224  * @timer:      pointer to either a timer_list or a hrtimer
 225  * @pid:        the pid of the task which set up the timer
 226  * @startf:     pointer to the function which did the timer setup
 227  * @timerf:     pointer to the timer callback function of the timer
 228  * @comm:       name of the process which set up the timer
 229  *
 230  * When the timer is already registered, then the event counter is
 231  * incremented. Otherwise the timer is registered in a free slot.
 232  */
 233 void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
 234                               void *timerf, char * comm)
 235 {
 236         /*
 237          * It doesnt matter which lock we take:
 238          */
 239         spinlock_t *lock = &per_cpu(lookup_lock, raw_smp_processor_id());
 240         struct entry *entry, input;
 241         unsigned long flags;
 242
 243         input.timer = timer;
 244         input.start_func = startf;
 245         input.expire_func = timerf;
 246         input.pid = pid;
 247
 248         spin_lock_irqsave(lock, flags);
 249         if (!active)
 250                 goto out_unlock;
 251
 252         entry = tstat_lookup(&input, comm);
 253         if (likely(entry))
 254                 entry->count++;
 255         else
 256                 atomic_inc(&overflow_count);
 257
 258  out_unlock:
 259         spin_unlock_irqrestore(lock, flags);
 260 }
 261
 262 static void print_name_offset(struct seq_file *m, unsigned long addr)
 263 {
 264         char symname[KSYM_NAME_LEN+1];
 265
 266         if (lookup_symbol_name(addr, symname) < 0)
 267                 seq_printf(m, "<%p>", (void *)addr);
 268         else
 269                 seq_printf(m, "%s", symname);
 270 }
 271
 272 static int tstats_show(struct seq_file *m, void *v)
 273 {
 274         struct timespec period;
 275         struct entry *entry;
 276         unsigned long ms;
 277         long events = 0;
 278         ktime_t time;
 279         int i;
 280
 281         mutex_lock(&show_mutex);
 282         /*
 283          * If still active then calculate up to now:
 284          */
 285         if (active)
 286                 time_stop = ktime_get();
 287
 288         time = ktime_sub(time_stop, time_start);
 289
 290         period = ktime_to_timespec(time);
 291         ms = period.tv_nsec / 1000000;
 292
 293         seq_puts(m, "Timer Stats Version: v0.1\n");
 294         seq_printf(m, "Sample period: %ld.%03ld s\n", period.tv_sec, ms);
 295         if (atomic_read(&overflow_count))
 296                 seq_printf(m, "Overflow: %d entries\n",
 297                         atomic_read(&overflow_count));
 298
 299         for (i = 0; i < nr_entries; i++) {
 300                 entry = entries + i;
 301                 seq_printf(m, "%4lu, %5d %-16s ",
 302                                 entry->count, entry->pid, entry->comm);
 303
 304                 print_name_offset(m, (unsigned long)entry->start_func);
 305                 seq_puts(m, " (");
 306                 print_name_offset(m, (unsigned long)entry->expire_func);
 307                 seq_puts(m, ")\n");
 308
 309                 events += entry->count;
 310         }
 311
 312         ms += period.tv_sec * 1000;
 313         if (!ms)
 314                 ms = 1;
 315
 316         if (events && period.tv_sec)
 317                 seq_printf(m, "%ld total events, %ld.%ld events/sec\n", events,
 318                            events / period.tv_sec, events * 1000 / ms);
 319         else
 320                 seq_printf(m, "%ld total events\n", events);
 321
 322         mutex_unlock(&show_mutex);
 323
 324         return 0;
 325 }
 326
 327 /*
 328  * After a state change, make sure all concurrent lookup/update
 329  * activities have stopped:
 330  */
 331 static void sync_access(void)
 332 {
 333         unsigned long flags;
 334         int cpu;
 335
 336         for_each_online_cpu(cpu) {
 337                 spin_lock_irqsave(&per_cpu(lookup_lock, cpu), flags);
 338                 /* nothing */
 339                 spin_unlock_irqrestore(&per_cpu(lookup_lock, cpu), flags);
 340         }
 341 }
 342
 343 static ssize_t tstats_write(struct file *file, const char __user *buf,
 344                             size_t count, loff_t *offs)
 345 {
 346         char ctl[2];
 347
 348         if (count != 2 || *offs)
 349                 return -EINVAL;
 350
 351         if (copy_from_user(ctl, buf, count))
 352                 return -EFAULT;
 353
 354         mutex_lock(&show_mutex);
 355         switch (ctl[0]) {
 356         case '0':
 357                 if (active) {
 358                         active = 0;
 359                         time_stop = ktime_get();
 360                         sync_access();
 361                 }
 362                 break;
 363         case '1':
 364                 if (!active) {
 365                         reset_entries();
 366                         time_start = ktime_get();
 367                         smp_mb();
 368                         active = 1;
 369                 }
 370                 break;
 371         default:
 372                 count = -EINVAL;
 373         }
 374         mutex_unlock(&show_mutex);
 375
 376         return count;
 377 }
 378
 379 static int tstats_open(struct inode *inode, struct file *filp)
 380 {
 381         return single_open(filp, tstats_show, NULL);
 382 }
 383
 384 static struct file_operations tstats_fops = {
 385         .open           = tstats_open,
 386         .read           = seq_read,
 387         .write          = tstats_write,
 388         .llseek         = seq_lseek,
 389         .release        = seq_release,
 390 };
 391
 392 void __init init_timer_stats(void)
 393 {
 394         int cpu;
 395
 396         for_each_possible_cpu(cpu)
 397                 spin_lock_init(&per_cpu(lookup_lock, cpu));
 398 }
 399
 400 static int __init init_tstats_procfs(void)
 401 {
 402         struct proc_dir_entry *pe;
 403
 404         pe = create_proc_entry("timer_stats", 0644, NULL);
 405         if (!pe)
 406                 return -ENOMEM;
 407
 408         pe->proc_fops = &tstats_fops;
 409
 410         return 0;
 411 }
 412 __initcall(init_tstats_procfs);