drivers/cpufreq/cpufreq_ondemand.c

   1 /*
   2  *  drivers/cpufreq/cpufreq_ondemand.c
   3  *
   4  *  Copyright (C)  2001 Russell King
   5  *            (C)  2003 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>.
   6  *                      Jun Nakajima <jun.nakajima@intel.com>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  */
  12
  13 #include <linux/kernel.h>
  14 #include <linux/module.h>
  15 #include <linux/init.h>
  16 #include <linux/cpufreq.h>
  17 #include <linux/cpu.h>
  18 #include <linux/jiffies.h>
  19 #include <linux/kernel_stat.h>
  20 #include <linux/mutex.h>
  21
  22 /*
  23  * dbs is used in this file as a shortform for demandbased switching
  24  * It helps to keep variable names smaller, simpler
  25  */
  26
  27 #define DEF_FREQUENCY_UP_THRESHOLD              (80)
  28 #define MIN_FREQUENCY_UP_THRESHOLD              (11)
  29 #define MAX_FREQUENCY_UP_THRESHOLD              (100)
  30
  31 /*
  32  * The polling frequency of this governor depends on the capability of
  33  * the processor. Default polling frequency is 1000 times the transition
  34  * latency of the processor. The governor will work on any processor with
  35  * transition latency <= 10mS, using appropriate sampling
  36  * rate.
  37  * For CPUs with transition latency > 10mS (mostly drivers with CPUFREQ_ETERNAL)
  38  * this governor will not work.
  39  * All times here are in uS.
  40  */
  41 static unsigned int def_sampling_rate;
  42 #define MIN_SAMPLING_RATE_RATIO                 (2)
  43 /* for correct statistics, we need at least 10 ticks between each measure */
  44 #define MIN_STAT_SAMPLING_RATE                  (MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10))
  45 #define MIN_SAMPLING_RATE                       (def_sampling_rate / MIN_SAMPLING_RATE_RATIO)
  46 #define MAX_SAMPLING_RATE                       (500 * def_sampling_rate)
  47 #define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER    (1000)
  48 #define TRANSITION_LATENCY_LIMIT                (10 * 1000)
  49
  50 static void do_dbs_timer(struct work_struct *work);
  51
  52 /* Sampling types */
  53 enum dbs_sample {DBS_NORMAL_SAMPLE, DBS_SUB_SAMPLE};
  54
  55 struct cpu_dbs_info_s {
  56         cputime64_t prev_cpu_idle;
  57         cputime64_t prev_cpu_wall;
  58         struct cpufreq_policy *cur_policy;
  59         struct delayed_work work;
  60         enum dbs_sample sample_type;
  61         unsigned int enable;
  62         struct cpufreq_frequency_table *freq_table;
  63         unsigned int freq_lo;
  64         unsigned int freq_lo_jiffies;
  65         unsigned int freq_hi_jiffies;
  66 };
  67 static DEFINE_PER_CPU(struct cpu_dbs_info_s, cpu_dbs_info);
  68
  69 static unsigned int dbs_enable; /* number of CPUs using this policy */
  70
  71 /*
  72  * DEADLOCK ALERT! There is a ordering requirement between cpu_hotplug
  73  * lock and dbs_mutex. cpu_hotplug lock should always be held before
  74  * dbs_mutex. If any function that can potentially take cpu_hotplug lock
  75  * (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then
  76  * cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock
  77  * is recursive for the same process. -Venki
  78  */
  79 static DEFINE_MUTEX(dbs_mutex);
  80
  81 static struct workqueue_struct  *kondemand_wq;
  82
  83 static struct dbs_tuners {
  84         unsigned int sampling_rate;
  85         unsigned int up_threshold;
  86         unsigned int ignore_nice;
  87         unsigned int powersave_bias;
  88 } dbs_tuners_ins = {
  89         .up_threshold = DEF_FREQUENCY_UP_THRESHOLD,
  90         .ignore_nice = 0,
  91         .powersave_bias = 0,
  92 };
  93
  94 static inline cputime64_t get_cpu_idle_time(unsigned int cpu)
  95 {
  96         cputime64_t retval;
  97
  98         retval = cputime64_add(kstat_cpu(cpu).cpustat.idle,
  99                         kstat_cpu(cpu).cpustat.iowait);
 100
 101         if (dbs_tuners_ins.ignore_nice)
 102                 retval = cputime64_add(retval, kstat_cpu(cpu).cpustat.nice);
 103
 104         return retval;
 105 }
 106
 107 /*
 108  * Find right freq to be set now with powersave_bias on.
 109  * Returns the freq_hi to be used right now and will set freq_hi_jiffies,
 110  * freq_lo, and freq_lo_jiffies in percpu area for averaging freqs.
 111  */
 112 static unsigned int powersave_bias_target(struct cpufreq_policy *policy,
 113                                           unsigned int freq_next,
 114                                           unsigned int relation)
 115 {
 116         unsigned int freq_req, freq_reduc, freq_avg;
 117         unsigned int freq_hi, freq_lo;
 118         unsigned int index = 0;
 119         unsigned int jiffies_total, jiffies_hi, jiffies_lo;
 120         struct cpu_dbs_info_s *dbs_info = &per_cpu(cpu_dbs_info, policy->cpu);
 121
 122         if (!dbs_info->freq_table) {
 123                 dbs_info->freq_lo = 0;
 124                 dbs_info->freq_lo_jiffies = 0;
 125                 return freq_next;
 126         }
 127
 128         cpufreq_frequency_table_target(policy, dbs_info->freq_table, freq_next,
 129                         relation, &index);
 130         freq_req = dbs_info->freq_table[index].frequency;
 131         freq_reduc = freq_req * dbs_tuners_ins.powersave_bias / 1000;
 132         freq_avg = freq_req - freq_reduc;
 133
 134         /* Find freq bounds for freq_avg in freq_table */
 135         index = 0;
 136         cpufreq_frequency_table_target(policy, dbs_info->freq_table, freq_avg,
 137                         CPUFREQ_RELATION_H, &index);
 138         freq_lo = dbs_info->freq_table[index].frequency;
 139         index = 0;
 140         cpufreq_frequency_table_target(policy, dbs_info->freq_table, freq_avg,
 141                         CPUFREQ_RELATION_L, &index);
 142         freq_hi = dbs_info->freq_table[index].frequency;
 143
 144         /* Find out how long we have to be in hi and lo freqs */
 145         if (freq_hi == freq_lo) {
 146                 dbs_info->freq_lo = 0;
 147                 dbs_info->freq_lo_jiffies = 0;
 148                 return freq_lo;
 149         }
 150         jiffies_total = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
 151         jiffies_hi = (freq_avg - freq_lo) * jiffies_total;
 152         jiffies_hi += ((freq_hi - freq_lo) / 2);
 153         jiffies_hi /= (freq_hi - freq_lo);
 154         jiffies_lo = jiffies_total - jiffies_hi;
 155         dbs_info->freq_lo = freq_lo;
 156         dbs_info->freq_lo_jiffies = jiffies_lo;
 157         dbs_info->freq_hi_jiffies = jiffies_hi;
 158         return freq_hi;
 159 }
 160
 161 static void ondemand_powersave_bias_init(void)
 162 {
 163         int i;
 164         for_each_online_cpu(i) {
 165                 struct cpu_dbs_info_s *dbs_info = &per_cpu(cpu_dbs_info, i);
 166                 dbs_info->freq_table = cpufreq_frequency_get_table(i);
 167                 dbs_info->freq_lo = 0;
 168         }
 169 }
 170
 171 /************************** sysfs interface ************************/
 172 static ssize_t show_sampling_rate_max(struct cpufreq_policy *policy, char *buf)
 173 {
 174         return sprintf (buf, "%u\n", MAX_SAMPLING_RATE);
 175 }
 176
 177 static ssize_t show_sampling_rate_min(struct cpufreq_policy *policy, char *buf)
 178 {
 179         return sprintf (buf, "%u\n", MIN_SAMPLING_RATE);
 180 }
 181
 182 #define define_one_ro(_name)            \
 183 static struct freq_attr _name =         \
 184 __ATTR(_name, 0444, show_##_name, NULL)
 185
 186 define_one_ro(sampling_rate_max);
 187 define_one_ro(sampling_rate_min);
 188
 189 /* cpufreq_ondemand Governor Tunables */
 190 #define show_one(file_name, object)                                     \
 191 static ssize_t show_##file_name                                         \
 192 (struct cpufreq_policy *unused, char *buf)                              \
 193 {                                                                       \
 194         return sprintf(buf, "%u\n", dbs_tuners_ins.object);             \
 195 }
 196 show_one(sampling_rate, sampling_rate);
 197 show_one(up_threshold, up_threshold);
 198 show_one(ignore_nice_load, ignore_nice);
 199 show_one(powersave_bias, powersave_bias);
 200
 201 static ssize_t store_sampling_rate(struct cpufreq_policy *unused,
 202                 const char *buf, size_t count)
 203 {
 204         unsigned int input;
 205         int ret;
 206         ret = sscanf(buf, "%u", &input);
 207
 208         mutex_lock(&dbs_mutex);
 209         if (ret != 1 || input > MAX_SAMPLING_RATE || input < MIN_SAMPLING_RATE) {
 210                 mutex_unlock(&dbs_mutex);
 211                 return -EINVAL;
 212         }
 213
 214         dbs_tuners_ins.sampling_rate = input;
 215         mutex_unlock(&dbs_mutex);
 216
 217         return count;
 218 }
 219
 220 static ssize_t store_up_threshold(struct cpufreq_policy *unused,
 221                 const char *buf, size_t count)
 222 {
 223         unsigned int input;
 224         int ret;
 225         ret = sscanf(buf, "%u", &input);
 226
 227         mutex_lock(&dbs_mutex);
 228         if (ret != 1 || input > MAX_FREQUENCY_UP_THRESHOLD ||
 229                         input < MIN_FREQUENCY_UP_THRESHOLD) {
 230                 mutex_unlock(&dbs_mutex);
 231                 return -EINVAL;
 232         }
 233
 234         dbs_tuners_ins.up_threshold = input;
 235         mutex_unlock(&dbs_mutex);
 236
 237         return count;
 238 }
 239
 240 static ssize_t store_ignore_nice_load(struct cpufreq_policy *policy,
 241                 const char *buf, size_t count)
 242 {
 243         unsigned int input;
 244         int ret;
 245
 246         unsigned int j;
 247
 248         ret = sscanf(buf, "%u", &input);
 249         if ( ret != 1 )
 250                 return -EINVAL;
 251
 252         if ( input > 1 )
 253                 input = 1;
 254
 255         mutex_lock(&dbs_mutex);
 256         if ( input == dbs_tuners_ins.ignore_nice ) { /* nothing to do */
 257                 mutex_unlock(&dbs_mutex);
 258                 return count;
 259         }
 260         dbs_tuners_ins.ignore_nice = input;
 261
 262         /* we need to re-evaluate prev_cpu_idle */
 263         for_each_online_cpu(j) {
 264                 struct cpu_dbs_info_s *dbs_info;
 265                 dbs_info = &per_cpu(cpu_dbs_info, j);
 266                 dbs_info->prev_cpu_idle = get_cpu_idle_time(j);
 267                 dbs_info->prev_cpu_wall = get_jiffies_64();
 268         }
 269         mutex_unlock(&dbs_mutex);
 270
 271         return count;
 272 }
 273
 274 static ssize_t store_powersave_bias(struct cpufreq_policy *unused,
 275                 const char *buf, size_t count)
 276 {
 277         unsigned int input;
 278         int ret;
 279         ret = sscanf(buf, "%u", &input);
 280
 281         if (ret != 1)
 282                 return -EINVAL;
 283
 284         if (input > 1000)
 285                 input = 1000;
 286
 287         mutex_lock(&dbs_mutex);
 288         dbs_tuners_ins.powersave_bias = input;
 289         ondemand_powersave_bias_init();
 290         mutex_unlock(&dbs_mutex);
 291
 292         return count;
 293 }
 294
 295 #define define_one_rw(_name) \
 296 static struct freq_attr _name = \
 297 __ATTR(_name, 0644, show_##_name, store_##_name)
 298
 299 define_one_rw(sampling_rate);
 300 define_one_rw(up_threshold);
 301 define_one_rw(ignore_nice_load);
 302 define_one_rw(powersave_bias);
 303
 304 static struct attribute * dbs_attributes[] = {
 305         &sampling_rate_max.attr,
 306         &sampling_rate_min.attr,
 307         &sampling_rate.attr,
 308         &up_threshold.attr,
 309         &ignore_nice_load.attr,
 310         &powersave_bias.attr,
 311         NULL
 312 };
 313
 314 static struct attribute_group dbs_attr_group = {
 315         .attrs = dbs_attributes,
 316         .name = "ondemand",
 317 };
 318
 319 /************************** sysfs end ************************/
 320
 321 static void dbs_check_cpu(struct cpu_dbs_info_s *this_dbs_info)
 322 {
 323         unsigned int idle_ticks, total_ticks;
 324         unsigned int load;
 325         cputime64_t cur_jiffies;
 326
 327         struct cpufreq_policy *policy;
 328         unsigned int j;
 329
 330         if (!this_dbs_info->enable)
 331                 return;
 332
 333         this_dbs_info->freq_lo = 0;
 334         policy = this_dbs_info->cur_policy;
 335         cur_jiffies = jiffies64_to_cputime64(get_jiffies_64());
 336         total_ticks = (unsigned int) cputime64_sub(cur_jiffies,
 337                         this_dbs_info->prev_cpu_wall);
 338         this_dbs_info->prev_cpu_wall = cur_jiffies;
 339         if (!total_ticks)
 340                 return;
 341         /*
 342          * Every sampling_rate, we check, if current idle time is less
 343          * than 20% (default), then we try to increase frequency
 344          * Every sampling_rate, we look for a the lowest
 345          * frequency which can sustain the load while keeping idle time over
 346          * 30%. If such a frequency exist, we try to decrease to this frequency.
 347          *
 348          * Any frequency increase takes it to the maximum frequency.
 349          * Frequency reduction happens at minimum steps of
 350          * 5% (default) of current frequency
 351          */
 352
 353         /* Get Idle Time */
 354         idle_ticks = UINT_MAX;
 355         for_each_cpu_mask(j, policy->cpus) {
 356                 cputime64_t total_idle_ticks;
 357                 unsigned int tmp_idle_ticks;
 358                 struct cpu_dbs_info_s *j_dbs_info;
 359
 360                 j_dbs_info = &per_cpu(cpu_dbs_info, j);
 361                 total_idle_ticks = get_cpu_idle_time(j);
 362                 tmp_idle_ticks = (unsigned int) cputime64_sub(total_idle_ticks,
 363                                 j_dbs_info->prev_cpu_idle);
 364                 j_dbs_info->prev_cpu_idle = total_idle_ticks;
 365
 366                 if (tmp_idle_ticks < idle_ticks)
 367                         idle_ticks = tmp_idle_ticks;
 368         }
 369         load = (100 * (total_ticks - idle_ticks)) / total_ticks;
 370
 371         /* Check for frequency increase */
 372         if (load > dbs_tuners_ins.up_threshold) {
 373                 /* if we are already at full speed then break out early */
 374                 if (!dbs_tuners_ins.powersave_bias) {
 375                         if (policy->cur == policy->max)
 376                                 return;
 377
 378                         __cpufreq_driver_target(policy, policy->max,
 379                                 CPUFREQ_RELATION_H);
 380                 } else {
 381                         int freq = powersave_bias_target(policy, policy->max,
 382                                         CPUFREQ_RELATION_H);
 383                         __cpufreq_driver_target(policy, freq,
 384                                 CPUFREQ_RELATION_L);
 385                 }
 386                 return;
 387         }
 388
 389         /* Check for frequency decrease */
 390         /* if we cannot reduce the frequency anymore, break out early */
 391         if (policy->cur == policy->min)
 392                 return;
 393
 394         /*
 395          * The optimal frequency is the frequency that is the lowest that
 396          * can support the current CPU usage without triggering the up
 397          * policy. To be safe, we focus 10 points under the threshold.
 398          */
 399         if (load < (dbs_tuners_ins.up_threshold - 10)) {
 400                 unsigned int freq_next = (policy->cur * load) /
 401                         (dbs_tuners_ins.up_threshold - 10);
 402                 if (!dbs_tuners_ins.powersave_bias) {
 403                         __cpufreq_driver_target(policy, freq_next,
 404                                         CPUFREQ_RELATION_L);
 405                 } else {
 406                         int freq = powersave_bias_target(policy, freq_next,
 407                                         CPUFREQ_RELATION_L);
 408                         __cpufreq_driver_target(policy, freq,
 409                                 CPUFREQ_RELATION_L);
 410                 }
 411         }
 412 }
 413
 414 static void do_dbs_timer(struct work_struct *work)
 415 {
 416         unsigned int cpu = smp_processor_id();
 417         struct cpu_dbs_info_s *dbs_info = &per_cpu(cpu_dbs_info, cpu);
 418         enum dbs_sample sample_type = dbs_info->sample_type;
 419         /* We want all CPUs to do sampling nearly on same jiffy */
 420         int delay = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
 421
 422         /* Permit rescheduling of this work item */
 423         work_release(work);
 424
 425         delay -= jiffies % delay;
 426
 427         if (!dbs_info->enable)
 428                 return;
 429         /* Common NORMAL_SAMPLE setup */
 430         dbs_info->sample_type = DBS_NORMAL_SAMPLE;
 431         if (!dbs_tuners_ins.powersave_bias ||
 432             sample_type == DBS_NORMAL_SAMPLE) {
 433                 lock_cpu_hotplug();
 434                 dbs_check_cpu(dbs_info);
 435                 unlock_cpu_hotplug();
 436                 if (dbs_info->freq_lo) {
 437                         /* Setup timer for SUB_SAMPLE */
 438                         dbs_info->sample_type = DBS_SUB_SAMPLE;
 439                         delay = dbs_info->freq_hi_jiffies;
 440                 }
 441         } else {
 442                 __cpufreq_driver_target(dbs_info->cur_policy,
 443                                         dbs_info->freq_lo,
 444                                         CPUFREQ_RELATION_H);
 445         }
 446         queue_delayed_work_on(cpu, kondemand_wq, &dbs_info->work, delay);
 447 }
 448
 449 static inline void dbs_timer_init(unsigned int cpu)
 450 {
 451         struct cpu_dbs_info_s *dbs_info = &per_cpu(cpu_dbs_info, cpu);
 452         /* We want all CPUs to do sampling nearly on same jiffy */
 453         int delay = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
 454         delay -= jiffies % delay;
 455
 456         ondemand_powersave_bias_init();
 457         INIT_DELAYED_WORK_NAR(&dbs_info->work, do_dbs_timer);
 458         dbs_info->sample_type = DBS_NORMAL_SAMPLE;
 459         queue_delayed_work_on(cpu, kondemand_wq, &dbs_info->work, delay);
 460 }
 461
 462 static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
 463 {
 464         dbs_info->enable = 0;
 465         cancel_delayed_work(&dbs_info->work);
 466         flush_workqueue(kondemand_wq);
 467 }
 468
 469 static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 470                                    unsigned int event)
 471 {
 472         unsigned int cpu = policy->cpu;
 473         struct cpu_dbs_info_s *this_dbs_info;
 474         unsigned int j;
 475
 476         this_dbs_info = &per_cpu(cpu_dbs_info, cpu);
 477
 478         switch (event) {
 479         case CPUFREQ_GOV_START:
 480                 if ((!cpu_online(cpu)) || (!policy->cur))
 481                         return -EINVAL;
 482
 483                 if (policy->cpuinfo.transition_latency >
 484                                 (TRANSITION_LATENCY_LIMIT * 1000)) {
 485                         printk(KERN_WARNING "ondemand governor failed to load "
 486                                "due to too long transition latency\n");
 487                         return -EINVAL;
 488                 }
 489                 if (this_dbs_info->enable) /* Already enabled */
 490                         break;
 491
 492                 mutex_lock(&dbs_mutex);
 493                 dbs_enable++;
 494                 if (dbs_enable == 1) {
 495                         kondemand_wq = create_workqueue("kondemand");
 496                         if (!kondemand_wq) {
 497                                 printk(KERN_ERR "Creation of kondemand failed\n");
 498                                 dbs_enable--;
 499                                 mutex_unlock(&dbs_mutex);
 500                                 return -ENOSPC;
 501                         }
 502                 }
 503                 for_each_cpu_mask(j, policy->cpus) {
 504                         struct cpu_dbs_info_s *j_dbs_info;
 505                         j_dbs_info = &per_cpu(cpu_dbs_info, j);
 506                         j_dbs_info->cur_policy = policy;
 507
 508                         j_dbs_info->prev_cpu_idle = get_cpu_idle_time(j);
 509                         j_dbs_info->prev_cpu_wall = get_jiffies_64();
 510                 }
 511                 this_dbs_info->enable = 1;
 512                 sysfs_create_group(&policy->kobj, &dbs_attr_group);
 513                 /*
 514                  * Start the timerschedule work, when this governor
 515                  * is used for first time
 516                  */
 517                 if (dbs_enable == 1) {
 518                         unsigned int latency;
 519                         /* policy latency is in nS. Convert it to uS first */
 520                         latency = policy->cpuinfo.transition_latency / 1000;
 521                         if (latency == 0)
 522                                 latency = 1;
 523
 524                         def_sampling_rate = latency *
 525                                         DEF_SAMPLING_RATE_LATENCY_MULTIPLIER;
 526
 527                         if (def_sampling_rate < MIN_STAT_SAMPLING_RATE)
 528                                 def_sampling_rate = MIN_STAT_SAMPLING_RATE;
 529
 530                         dbs_tuners_ins.sampling_rate = def_sampling_rate;
 531                 }
 532                 dbs_timer_init(policy->cpu);
 533
 534                 mutex_unlock(&dbs_mutex);
 535                 break;
 536
 537         case CPUFREQ_GOV_STOP:
 538                 mutex_lock(&dbs_mutex);
 539                 dbs_timer_exit(this_dbs_info);
 540                 sysfs_remove_group(&policy->kobj, &dbs_attr_group);
 541                 dbs_enable--;
 542                 if (dbs_enable == 0)
 543                         destroy_workqueue(kondemand_wq);
 544
 545                 mutex_unlock(&dbs_mutex);
 546
 547                 break;
 548
 549         case CPUFREQ_GOV_LIMITS:
 550                 mutex_lock(&dbs_mutex);
 551                 if (policy->max < this_dbs_info->cur_policy->cur)
 552                         __cpufreq_driver_target(this_dbs_info->cur_policy,
 553                                                 policy->max,
 554                                                 CPUFREQ_RELATION_H);
 555                 else if (policy->min > this_dbs_info->cur_policy->cur)
 556                         __cpufreq_driver_target(this_dbs_info->cur_policy,
 557                                                 policy->min,
 558                                                 CPUFREQ_RELATION_L);
 559                 mutex_unlock(&dbs_mutex);
 560                 break;
 561         }
 562         return 0;
 563 }
 564
 565 static struct cpufreq_governor cpufreq_gov_dbs = {
 566         .name = "ondemand",
 567         .governor = cpufreq_governor_dbs,
 568         .owner = THIS_MODULE,
 569 };
 570
 571 static int __init cpufreq_gov_dbs_init(void)
 572 {
 573         return cpufreq_register_governor(&cpufreq_gov_dbs);
 574 }
 575
 576 static void __exit cpufreq_gov_dbs_exit(void)
 577 {
 578         cpufreq_unregister_governor(&cpufreq_gov_dbs);
 579 }
 580
 581
 582 MODULE_AUTHOR("Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>");
 583 MODULE_AUTHOR("Alexey Starikovskiy <alexey.y.starikovskiy@intel.com>");
 584 MODULE_DESCRIPTION("'cpufreq_ondemand' - A dynamic cpufreq governor for "
 585                    "Low Latency Frequency Transition capable processors");
 586 MODULE_LICENSE("GPL");
 587
 588 module_init(cpufreq_gov_dbs_init);
 589 module_exit(cpufreq_gov_dbs_exit);