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_DOWN_DIFFERENTIAL         (10)
  28 #define DEF_FREQUENCY_UP_THRESHOLD              (80)
  29 #define MIN_FREQUENCY_UP_THRESHOLD              (11)
  30 #define MAX_FREQUENCY_UP_THRESHOLD              (100)
  31
  32 /*
  33  * The polling frequency of this governor depends on the capability of
  34  * the processor. Default polling frequency is 1000 times the transition
  35  * latency of the processor. The governor will work on any processor with
  36  * transition latency <= 10mS, using appropriate sampling
  37  * rate.
  38  * For CPUs with transition latency > 10mS (mostly drivers with CPUFREQ_ETERNAL)
  39  * this governor will not work.
  40  * All times here are in uS.
  41  */
  42 static unsigned int def_sampling_rate;
  43 #define MIN_SAMPLING_RATE_RATIO                 (2)
  44 /* for correct statistics, we need at least 10 ticks between each measure */
  45 #define MIN_STAT_SAMPLING_RATE                  \
  46                         (MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10))
  47 #define MIN_SAMPLING_RATE                       \
  48                         (def_sampling_rate / MIN_SAMPLING_RATE_RATIO)
  49 #define MAX_SAMPLING_RATE                       (500 * def_sampling_rate)
  50 #define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER    (1000)
  51 #define TRANSITION_LATENCY_LIMIT                (10 * 1000 * 1000)
  52
  53 static void do_dbs_timer(struct work_struct *work);
  54
  55 /* Sampling types */
  56 enum {DBS_NORMAL_SAMPLE, DBS_SUB_SAMPLE};
  57
  58 struct cpu_dbs_info_s {
  59         cputime64_t prev_cpu_idle;
  60         cputime64_t prev_cpu_wall;
  61         struct cpufreq_policy *cur_policy;
  62         struct delayed_work work;
  63         struct cpufreq_frequency_table *freq_table;
  64         unsigned int freq_lo;
  65         unsigned int freq_lo_jiffies;
  66         unsigned int freq_hi_jiffies;
  67         int cpu;
  68         unsigned int enable:1,
  69                      sample_type:1;
  70 };
  71 static DEFINE_PER_CPU(struct cpu_dbs_info_s, cpu_dbs_info);
  72
  73 static unsigned int dbs_enable; /* number of CPUs using this policy */
  74
  75 /*
  76  * DEADLOCK ALERT! There is a ordering requirement between cpu_hotplug
  77  * lock and dbs_mutex. cpu_hotplug lock should always be held before
  78  * dbs_mutex. If any function that can potentially take cpu_hotplug lock
  79  * (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then
  80  * cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock
  81  * is recursive for the same process. -Venki
  82  */
  83 static DEFINE_MUTEX(dbs_mutex);
  84
  85 static struct workqueue_struct  *kondemand_wq;
  86
  87 static struct dbs_tuners {
  88         unsigned int sampling_rate;
  89         unsigned int up_threshold;
  90         unsigned int down_differential;
  91         unsigned int ignore_nice;
  92         unsigned int powersave_bias;
  93 } dbs_tuners_ins = {
  94         .up_threshold = DEF_FREQUENCY_UP_THRESHOLD,
  95         .down_differential = DEF_FREQUENCY_DOWN_DIFFERENTIAL,
  96         .ignore_nice = 0,
  97         .powersave_bias = 0,
  98 };
  99
 100 static inline cputime64_t get_cpu_idle_time(unsigned int cpu, cputime64_t *wall)
 101 {
 102         cputime64_t idle_time;
 103         cputime64_t cur_wall_time;
 104         cputime64_t busy_time;
 105
 106         cur_wall_time = jiffies64_to_cputime64(get_jiffies_64());
 107         busy_time = cputime64_add(kstat_cpu(cpu).cpustat.user,
 108                         kstat_cpu(cpu).cpustat.system);
 109
 110         busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.irq);
 111         busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.softirq);
 112         busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.steal);
 113
 114         if (!dbs_tuners_ins.ignore_nice) {
 115                 busy_time = cputime64_add(busy_time,
 116                                 kstat_cpu(cpu).cpustat.nice);
 117         }
 118
 119         idle_time = cputime64_sub(cur_wall_time, busy_time);
 120         if (wall)
 121                 *wall = cur_wall_time;
 122
 123         return idle_time;
 124 }
 125
 126 /*
 127  * Find right freq to be set now with powersave_bias on.
 128  * Returns the freq_hi to be used right now and will set freq_hi_jiffies,
 129  * freq_lo, and freq_lo_jiffies in percpu area for averaging freqs.
 130  */
 131 static unsigned int powersave_bias_target(struct cpufreq_policy *policy,
 132                                           unsigned int freq_next,
 133                                           unsigned int relation)
 134 {
 135         unsigned int freq_req, freq_reduc, freq_avg;
 136         unsigned int freq_hi, freq_lo;
 137         unsigned int index = 0;
 138         unsigned int jiffies_total, jiffies_hi, jiffies_lo;
 139         struct cpu_dbs_info_s *dbs_info = &per_cpu(cpu_dbs_info, policy->cpu);
 140
 141         if (!dbs_info->freq_table) {
 142                 dbs_info->freq_lo = 0;
 143                 dbs_info->freq_lo_jiffies = 0;
 144                 return freq_next;
 145         }
 146
 147         cpufreq_frequency_table_target(policy, dbs_info->freq_table, freq_next,
 148                         relation, &index);
 149         freq_req = dbs_info->freq_table[index].frequency;
 150         freq_reduc = freq_req * dbs_tuners_ins.powersave_bias / 1000;
 151         freq_avg = freq_req - freq_reduc;
 152
 153         /* Find freq bounds for freq_avg in freq_table */
 154         index = 0;
 155         cpufreq_frequency_table_target(policy, dbs_info->freq_table, freq_avg,
 156                         CPUFREQ_RELATION_H, &index);
 157         freq_lo = dbs_info->freq_table[index].frequency;
 158         index = 0;
 159         cpufreq_frequency_table_target(policy, dbs_info->freq_table, freq_avg,
 160                         CPUFREQ_RELATION_L, &index);
 161         freq_hi = dbs_info->freq_table[index].frequency;
 162
 163         /* Find out how long we have to be in hi and lo freqs */
 164         if (freq_hi == freq_lo) {
 165                 dbs_info->freq_lo = 0;
 166                 dbs_info->freq_lo_jiffies = 0;
 167                 return freq_lo;
 168         }
 169         jiffies_total = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
 170         jiffies_hi = (freq_avg - freq_lo) * jiffies_total;
 171         jiffies_hi += ((freq_hi - freq_lo) / 2);
 172         jiffies_hi /= (freq_hi - freq_lo);
 173         jiffies_lo = jiffies_total - jiffies_hi;
 174         dbs_info->freq_lo = freq_lo;
 175         dbs_info->freq_lo_jiffies = jiffies_lo;
 176         dbs_info->freq_hi_jiffies = jiffies_hi;
 177         return freq_hi;
 178 }
 179
 180 static void ondemand_powersave_bias_init(void)
 181 {
 182         int i;
 183         for_each_online_cpu(i) {
 184                 struct cpu_dbs_info_s *dbs_info = &per_cpu(cpu_dbs_info, i);
 185                 dbs_info->freq_table = cpufreq_frequency_get_table(i);
 186                 dbs_info->freq_lo = 0;
 187         }
 188 }
 189
 190 /************************** sysfs interface ************************/
 191 static ssize_t show_sampling_rate_max(struct cpufreq_policy *policy, char *buf)
 192 {
 193         return sprintf (buf, "%u\n", MAX_SAMPLING_RATE);
 194 }
 195
 196 static ssize_t show_sampling_rate_min(struct cpufreq_policy *policy, char *buf)
 197 {
 198         return sprintf (buf, "%u\n", MIN_SAMPLING_RATE);
 199 }
 200
 201 #define define_one_ro(_name)            \
 202 static struct freq_attr _name =         \
 203 __ATTR(_name, 0444, show_##_name, NULL)
 204
 205 define_one_ro(sampling_rate_max);
 206 define_one_ro(sampling_rate_min);
 207
 208 /* cpufreq_ondemand Governor Tunables */
 209 #define show_one(file_name, object)                                     \
 210 static ssize_t show_##file_name                                         \
 211 (struct cpufreq_policy *unused, char *buf)                              \
 212 {                                                                       \
 213         return sprintf(buf, "%u\n", dbs_tuners_ins.object);             \
 214 }
 215 show_one(sampling_rate, sampling_rate);
 216 show_one(up_threshold, up_threshold);
 217 show_one(ignore_nice_load, ignore_nice);
 218 show_one(powersave_bias, powersave_bias);
 219
 220 static ssize_t store_sampling_rate(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_SAMPLING_RATE
 229                      || input < MIN_SAMPLING_RATE) {
 230                 mutex_unlock(&dbs_mutex);
 231                 return -EINVAL;
 232         }
 233
 234         dbs_tuners_ins.sampling_rate = input;
 235         mutex_unlock(&dbs_mutex);
 236
 237         return count;
 238 }
 239
 240 static ssize_t store_up_threshold(struct cpufreq_policy *unused,
 241                 const char *buf, size_t count)
 242 {
 243         unsigned int input;
 244         int ret;
 245         ret = sscanf(buf, "%u", &input);
 246
 247         mutex_lock(&dbs_mutex);
 248         if (ret != 1 || input > MAX_FREQUENCY_UP_THRESHOLD ||
 249                         input < MIN_FREQUENCY_UP_THRESHOLD) {
 250                 mutex_unlock(&dbs_mutex);
 251                 return -EINVAL;
 252         }
 253
 254         dbs_tuners_ins.up_threshold = input;
 255         mutex_unlock(&dbs_mutex);
 256
 257         return count;
 258 }
 259
 260 static ssize_t store_ignore_nice_load(struct cpufreq_policy *policy,
 261                 const char *buf, size_t count)
 262 {
 263         unsigned int input;
 264         int ret;
 265
 266         unsigned int j;
 267
 268         ret = sscanf(buf, "%u", &input);
 269         if ( ret != 1 )
 270                 return -EINVAL;
 271
 272         if ( input > 1 )
 273                 input = 1;
 274
 275         mutex_lock(&dbs_mutex);
 276         if ( input == dbs_tuners_ins.ignore_nice ) { /* nothing to do */
 277                 mutex_unlock(&dbs_mutex);
 278                 return count;
 279         }
 280         dbs_tuners_ins.ignore_nice = input;
 281
 282         /* we need to re-evaluate prev_cpu_idle */
 283         for_each_online_cpu(j) {
 284                 struct cpu_dbs_info_s *dbs_info;
 285                 dbs_info = &per_cpu(cpu_dbs_info, j);
 286                 dbs_info->prev_cpu_idle = get_cpu_idle_time(j,
 287                                                 &dbs_info->prev_cpu_wall);
 288         }
 289         mutex_unlock(&dbs_mutex);
 290
 291         return count;
 292 }
 293
 294 static ssize_t store_powersave_bias(struct cpufreq_policy *unused,
 295                 const char *buf, size_t count)
 296 {
 297         unsigned int input;
 298         int ret;
 299         ret = sscanf(buf, "%u", &input);
 300
 301         if (ret != 1)
 302                 return -EINVAL;
 303
 304         if (input > 1000)
 305                 input = 1000;
 306
 307         mutex_lock(&dbs_mutex);
 308         dbs_tuners_ins.powersave_bias = input;
 309         ondemand_powersave_bias_init();
 310         mutex_unlock(&dbs_mutex);
 311
 312         return count;
 313 }
 314
 315 #define define_one_rw(_name) \
 316 static struct freq_attr _name = \
 317 __ATTR(_name, 0644, show_##_name, store_##_name)
 318
 319 define_one_rw(sampling_rate);
 320 define_one_rw(up_threshold);
 321 define_one_rw(ignore_nice_load);
 322 define_one_rw(powersave_bias);
 323
 324 static struct attribute * dbs_attributes[] = {
 325         &sampling_rate_max.attr,
 326         &sampling_rate_min.attr,
 327         &sampling_rate.attr,
 328         &up_threshold.attr,
 329         &ignore_nice_load.attr,
 330         &powersave_bias.attr,
 331         NULL
 332 };
 333
 334 static struct attribute_group dbs_attr_group = {
 335         .attrs = dbs_attributes,
 336         .name = "ondemand",
 337 };
 338
 339 /************************** sysfs end ************************/
 340
 341 static void dbs_check_cpu(struct cpu_dbs_info_s *this_dbs_info)
 342 {
 343         unsigned int max_load_freq;
 344
 345         struct cpufreq_policy *policy;
 346         unsigned int j;
 347
 348         if (!this_dbs_info->enable)
 349                 return;
 350
 351         this_dbs_info->freq_lo = 0;
 352         policy = this_dbs_info->cur_policy;
 353
 354         /*
 355          * Every sampling_rate, we check, if current idle time is less
 356          * than 20% (default), then we try to increase frequency
 357          * Every sampling_rate, we look for a the lowest
 358          * frequency which can sustain the load while keeping idle time over
 359          * 30%. If such a frequency exist, we try to decrease to this frequency.
 360          *
 361          * Any frequency increase takes it to the maximum frequency.
 362          * Frequency reduction happens at minimum steps of
 363          * 5% (default) of current frequency
 364          */
 365
 366         /* Get Absolute Load - in terms of freq */
 367         max_load_freq = 0;
 368
 369         for_each_cpu_mask_nr(j, policy->cpus) {
 370                 struct cpu_dbs_info_s *j_dbs_info;
 371                 cputime64_t cur_wall_time, cur_idle_time;
 372                 unsigned int idle_time, wall_time;
 373                 unsigned int load, load_freq;
 374                 int freq_avg;
 375
 376                 j_dbs_info = &per_cpu(cpu_dbs_info, j);
 377
 378                 cur_idle_time = get_cpu_idle_time(j, &cur_wall_time);
 379
 380                 wall_time = (unsigned int) cputime64_sub(cur_wall_time,
 381                                 j_dbs_info->prev_cpu_wall);
 382                 j_dbs_info->prev_cpu_wall = cur_wall_time;
 383
 384                 idle_time = (unsigned int) cputime64_sub(cur_idle_time,
 385                                 j_dbs_info->prev_cpu_idle);
 386                 j_dbs_info->prev_cpu_idle = cur_idle_time;
 387
 388                 if (unlikely(!wall_time || wall_time < idle_time))
 389                         continue;
 390
 391                 load = 100 * (wall_time - idle_time) / wall_time;
 392
 393                 freq_avg = __cpufreq_driver_getavg(policy, j);
 394                 if (freq_avg <= 0)
 395                         freq_avg = policy->cur;
 396
 397                 load_freq = load * freq_avg;
 398                 if (load_freq > max_load_freq)
 399                         max_load_freq = load_freq;
 400         }
 401
 402         /* Check for frequency increase */
 403         if (max_load_freq > dbs_tuners_ins.up_threshold * policy->cur) {
 404                 /* if we are already at full speed then break out early */
 405                 if (!dbs_tuners_ins.powersave_bias) {
 406                         if (policy->cur == policy->max)
 407                                 return;
 408
 409                         __cpufreq_driver_target(policy, policy->max,
 410                                 CPUFREQ_RELATION_H);
 411                 } else {
 412                         int freq = powersave_bias_target(policy, policy->max,
 413                                         CPUFREQ_RELATION_H);
 414                         __cpufreq_driver_target(policy, freq,
 415                                 CPUFREQ_RELATION_L);
 416                 }
 417                 return;
 418         }
 419
 420         /* Check for frequency decrease */
 421         /* if we cannot reduce the frequency anymore, break out early */
 422         if (policy->cur == policy->min)
 423                 return;
 424
 425         /*
 426          * The optimal frequency is the frequency that is the lowest that
 427          * can support the current CPU usage without triggering the up
 428          * policy. To be safe, we focus 10 points under the threshold.
 429          */
 430         if (max_load_freq <
 431             (dbs_tuners_ins.up_threshold - dbs_tuners_ins.down_differential) *
 432              policy->cur) {
 433                 unsigned int freq_next;
 434                 freq_next = max_load_freq /
 435                                 (dbs_tuners_ins.up_threshold -
 436                                  dbs_tuners_ins.down_differential);
 437
 438                 if (!dbs_tuners_ins.powersave_bias) {
 439                         __cpufreq_driver_target(policy, freq_next,
 440                                         CPUFREQ_RELATION_L);
 441                 } else {
 442                         int freq = powersave_bias_target(policy, freq_next,
 443                                         CPUFREQ_RELATION_L);
 444                         __cpufreq_driver_target(policy, freq,
 445                                 CPUFREQ_RELATION_L);
 446                 }
 447         }
 448 }
 449
 450 static void do_dbs_timer(struct work_struct *work)
 451 {
 452         struct cpu_dbs_info_s *dbs_info =
 453                 container_of(work, struct cpu_dbs_info_s, work.work);
 454         unsigned int cpu = dbs_info->cpu;
 455         int sample_type = dbs_info->sample_type;
 456
 457         /* We want all CPUs to do sampling nearly on same jiffy */
 458         int delay = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
 459
 460         delay -= jiffies % delay;
 461
 462         if (lock_policy_rwsem_write(cpu) < 0)
 463                 return;
 464
 465         if (!dbs_info->enable) {
 466                 unlock_policy_rwsem_write(cpu);
 467                 return;
 468         }
 469
 470         /* Common NORMAL_SAMPLE setup */
 471         dbs_info->sample_type = DBS_NORMAL_SAMPLE;
 472         if (!dbs_tuners_ins.powersave_bias ||
 473             sample_type == DBS_NORMAL_SAMPLE) {
 474                 dbs_check_cpu(dbs_info);
 475                 if (dbs_info->freq_lo) {
 476                         /* Setup timer for SUB_SAMPLE */
 477                         dbs_info->sample_type = DBS_SUB_SAMPLE;
 478                         delay = dbs_info->freq_hi_jiffies;
 479                 }
 480         } else {
 481                 __cpufreq_driver_target(dbs_info->cur_policy,
 482                                         dbs_info->freq_lo,
 483                                         CPUFREQ_RELATION_H);
 484         }
 485         queue_delayed_work_on(cpu, kondemand_wq, &dbs_info->work, delay);
 486         unlock_policy_rwsem_write(cpu);
 487 }
 488
 489 static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
 490 {
 491         /* We want all CPUs to do sampling nearly on same jiffy */
 492         int delay = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
 493         delay -= jiffies % delay;
 494
 495         dbs_info->enable = 1;
 496         ondemand_powersave_bias_init();
 497         dbs_info->sample_type = DBS_NORMAL_SAMPLE;
 498         INIT_DELAYED_WORK_DEFERRABLE(&dbs_info->work, do_dbs_timer);
 499         queue_delayed_work_on(dbs_info->cpu, kondemand_wq, &dbs_info->work,
 500                               delay);
 501 }
 502
 503 static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
 504 {
 505         dbs_info->enable = 0;
 506         cancel_delayed_work(&dbs_info->work);
 507 }
 508
 509 static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 510                                    unsigned int event)
 511 {
 512         unsigned int cpu = policy->cpu;
 513         struct cpu_dbs_info_s *this_dbs_info;
 514         unsigned int j;
 515         int rc;
 516
 517         this_dbs_info = &per_cpu(cpu_dbs_info, cpu);
 518
 519         switch (event) {
 520         case CPUFREQ_GOV_START:
 521                 if ((!cpu_online(cpu)) || (!policy->cur))
 522                         return -EINVAL;
 523
 524                 if (this_dbs_info->enable) /* Already enabled */
 525                         break;
 526
 527                 mutex_lock(&dbs_mutex);
 528                 dbs_enable++;
 529
 530                 rc = sysfs_create_group(&policy->kobj, &dbs_attr_group);
 531                 if (rc) {
 532                         dbs_enable--;
 533                         mutex_unlock(&dbs_mutex);
 534                         return rc;
 535                 }
 536
 537                 for_each_cpu_mask_nr(j, policy->cpus) {
 538                         struct cpu_dbs_info_s *j_dbs_info;
 539                         j_dbs_info = &per_cpu(cpu_dbs_info, j);
 540                         j_dbs_info->cur_policy = policy;
 541
 542                         j_dbs_info->prev_cpu_idle = get_cpu_idle_time(j,
 543                                                 &j_dbs_info->prev_cpu_wall);
 544                 }
 545                 this_dbs_info->cpu = cpu;
 546                 /*
 547                  * Start the timerschedule work, when this governor
 548                  * is used for first time
 549                  */
 550                 if (dbs_enable == 1) {
 551                         unsigned int latency;
 552                         /* policy latency is in nS. Convert it to uS first */
 553                         latency = policy->cpuinfo.transition_latency / 1000;
 554                         if (latency == 0)
 555                                 latency = 1;
 556
 557                         def_sampling_rate = latency *
 558                                         DEF_SAMPLING_RATE_LATENCY_MULTIPLIER;
 559
 560                         if (def_sampling_rate < MIN_STAT_SAMPLING_RATE)
 561                                 def_sampling_rate = MIN_STAT_SAMPLING_RATE;
 562
 563                         dbs_tuners_ins.sampling_rate = def_sampling_rate;
 564                 }
 565                 dbs_timer_init(this_dbs_info);
 566
 567                 mutex_unlock(&dbs_mutex);
 568                 break;
 569
 570         case CPUFREQ_GOV_STOP:
 571                 mutex_lock(&dbs_mutex);
 572                 dbs_timer_exit(this_dbs_info);
 573                 sysfs_remove_group(&policy->kobj, &dbs_attr_group);
 574                 dbs_enable--;
 575                 mutex_unlock(&dbs_mutex);
 576
 577                 break;
 578
 579         case CPUFREQ_GOV_LIMITS:
 580                 mutex_lock(&dbs_mutex);
 581                 if (policy->max < this_dbs_info->cur_policy->cur)
 582                         __cpufreq_driver_target(this_dbs_info->cur_policy,
 583                                                 policy->max,
 584                                                 CPUFREQ_RELATION_H);
 585                 else if (policy->min > this_dbs_info->cur_policy->cur)
 586                         __cpufreq_driver_target(this_dbs_info->cur_policy,
 587                                                 policy->min,
 588                                                 CPUFREQ_RELATION_L);
 589                 mutex_unlock(&dbs_mutex);
 590                 break;
 591         }
 592         return 0;
 593 }
 594
 595 struct cpufreq_governor cpufreq_gov_ondemand = {
 596         .name                   = "ondemand",
 597         .governor               = cpufreq_governor_dbs,
 598         .max_transition_latency = TRANSITION_LATENCY_LIMIT,
 599         .owner                  = THIS_MODULE,
 600 };
 601 EXPORT_SYMBOL(cpufreq_gov_ondemand);
 602
 603 static int __init cpufreq_gov_dbs_init(void)
 604 {
 605         int err;
 606
 607         kondemand_wq = create_workqueue("kondemand");
 608         if (!kondemand_wq) {
 609                 printk(KERN_ERR "Creation of kondemand failed\n");
 610                 return -EFAULT;
 611         }
 612         err = cpufreq_register_governor(&cpufreq_gov_ondemand);
 613         if (err)
 614                 destroy_workqueue(kondemand_wq);
 615
 616         return err;
 617 }
 618
 619 static void __exit cpufreq_gov_dbs_exit(void)
 620 {
 621         cpufreq_unregister_governor(&cpufreq_gov_ondemand);
 622         destroy_workqueue(kondemand_wq);
 623 }
 624
 625
 626 MODULE_AUTHOR("Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>");
 627 MODULE_AUTHOR("Alexey Starikovskiy <alexey.y.starikovskiy@intel.com>");
 628 MODULE_DESCRIPTION("'cpufreq_ondemand' - A dynamic cpufreq governor for "
 629                    "Low Latency Frequency Transition capable processors");
 630 MODULE_LICENSE("GPL");
 631
 632 #ifdef CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND
 633 fs_initcall(cpufreq_gov_dbs_init);
 634 #else
 635 module_init(cpufreq_gov_dbs_init);
 636 #endif
 637 module_exit(cpufreq_gov_dbs_exit);