drivers/cpufreq/cpufreq_conservative.c

   1 /*
   2  *  drivers/cpufreq/cpufreq_conservative.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  *            (C)  2009 Alexander Clouter <alex@digriz.org.uk>
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License version 2 as
  11  * published by the Free Software Foundation.
  12  */
  13
  14 #include <linux/kernel.h>
  15 #include <linux/module.h>
  16 #include <linux/init.h>
  17 #include <linux/cpufreq.h>
  18 #include <linux/cpu.h>
  19 #include <linux/jiffies.h>
  20 #include <linux/kernel_stat.h>
  21 #include <linux/mutex.h>
  22 #include <linux/hrtimer.h>
  23 #include <linux/tick.h>
  24 #include <linux/ktime.h>
  25 #include <linux/sched.h>
  26
  27 /*
  28  * dbs is used in this file as a shortform for demandbased switching
  29  * It helps to keep variable names smaller, simpler
  30  */
  31
  32 #define DEF_FREQUENCY_UP_THRESHOLD              (80)
  33 #define DEF_FREQUENCY_DOWN_THRESHOLD            (20)
  34
  35 /*
  36  * The polling frequency of this governor depends on the capability of
  37  * the processor. Default polling frequency is 1000 times the transition
  38  * latency of the processor. The governor will work on any processor with
  39  * transition latency <= 10mS, using appropriate sampling
  40  * rate.
  41  * For CPUs with transition latency > 10mS (mostly drivers with CPUFREQ_ETERNAL)
  42  * this governor will not work.
  43  * All times here are in uS.
  44  */
  45 static unsigned int def_sampling_rate;
  46 #define MIN_SAMPLING_RATE_RATIO                 (2)
  47 /* for correct statistics, we need at least 10 ticks between each measure */
  48 #define MIN_STAT_SAMPLING_RATE                  \
  49                         (MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10))
  50 #define MIN_SAMPLING_RATE                       \
  51                         (def_sampling_rate / MIN_SAMPLING_RATE_RATIO)
  52 /* Above MIN_SAMPLING_RATE will vanish with its sysfs file soon
  53  * Define the minimal settable sampling rate to the greater of:
  54  *   - "HW transition latency" * 100 (same as default sampling / 10)
  55  *   - MIN_STAT_SAMPLING_RATE
  56  * To avoid that userspace shoots itself.
  57 */
  58 static unsigned int minimum_sampling_rate(void)
  59 {
  60         return max(def_sampling_rate / 10, MIN_STAT_SAMPLING_RATE);
  61 }
  62
  63 /* This will also vanish soon with removing sampling_rate_max */
  64 #define MAX_SAMPLING_RATE                       (500 * def_sampling_rate)
  65 #define LATENCY_MULTIPLIER                      (1000)
  66 #define DEF_SAMPLING_DOWN_FACTOR                (1)
  67 #define MAX_SAMPLING_DOWN_FACTOR                (10)
  68 #define TRANSITION_LATENCY_LIMIT                (10 * 1000 * 1000)
  69
  70 static void do_dbs_timer(struct work_struct *work);
  71
  72 struct cpu_dbs_info_s {
  73         cputime64_t prev_cpu_idle;
  74         cputime64_t prev_cpu_wall;
  75         cputime64_t prev_cpu_nice;
  76         struct cpufreq_policy *cur_policy;
  77         struct delayed_work work;
  78         unsigned int down_skip;
  79         unsigned int requested_freq;
  80         int cpu;
  81         unsigned int enable:1;
  82 };
  83 static DEFINE_PER_CPU(struct cpu_dbs_info_s, cpu_dbs_info);
  84
  85 static unsigned int dbs_enable; /* number of CPUs using this policy */
  86
  87 /*
  88  * DEADLOCK ALERT! There is a ordering requirement between cpu_hotplug
  89  * lock and dbs_mutex. cpu_hotplug lock should always be held before
  90  * dbs_mutex. If any function that can potentially take cpu_hotplug lock
  91  * (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then
  92  * cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock
  93  * is recursive for the same process. -Venki
  94  * DEADLOCK ALERT! (2) : do_dbs_timer() must not take the dbs_mutex, because it
  95  * would deadlock with cancel_delayed_work_sync(), which is needed for proper
  96  * raceless workqueue teardown.
  97  */
  98 static DEFINE_MUTEX(dbs_mutex);
  99
 100 static struct workqueue_struct  *kconservative_wq;
 101
 102 static struct dbs_tuners {
 103         unsigned int sampling_rate;
 104         unsigned int sampling_down_factor;
 105         unsigned int up_threshold;
 106         unsigned int down_threshold;
 107         unsigned int ignore_nice;
 108         unsigned int freq_step;
 109 } dbs_tuners_ins = {
 110         .up_threshold = DEF_FREQUENCY_UP_THRESHOLD,
 111         .down_threshold = DEF_FREQUENCY_DOWN_THRESHOLD,
 112         .sampling_down_factor = DEF_SAMPLING_DOWN_FACTOR,
 113         .ignore_nice = 0,
 114         .freq_step = 5,
 115 };
 116
 117 static inline cputime64_t get_cpu_idle_time_jiffy(unsigned int cpu,
 118                                                         cputime64_t *wall)
 119 {
 120         cputime64_t idle_time;
 121         cputime64_t cur_wall_time;
 122         cputime64_t busy_time;
 123
 124         cur_wall_time = jiffies64_to_cputime64(get_jiffies_64());
 125         busy_time = cputime64_add(kstat_cpu(cpu).cpustat.user,
 126                         kstat_cpu(cpu).cpustat.system);
 127
 128         busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.irq);
 129         busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.softirq);
 130         busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.steal);
 131         busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.nice);
 132
 133         idle_time = cputime64_sub(cur_wall_time, busy_time);
 134         if (wall)
 135                 *wall = cur_wall_time;
 136
 137         return idle_time;
 138 }
 139
 140 static inline cputime64_t get_cpu_idle_time(unsigned int cpu, cputime64_t *wall)
 141 {
 142         u64 idle_time = get_cpu_idle_time_us(cpu, wall);
 143
 144         if (idle_time == -1ULL)
 145                 return get_cpu_idle_time_jiffy(cpu, wall);
 146
 147         return idle_time;
 148 }
 149
 150 /* keep track of frequency transitions */
 151 static int
 152 dbs_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
 153                      void *data)
 154 {
 155         struct cpufreq_freqs *freq = data;
 156         struct cpu_dbs_info_s *this_dbs_info = &per_cpu(cpu_dbs_info,
 157                                                         freq->cpu);
 158
 159         struct cpufreq_policy *policy;
 160
 161         if (!this_dbs_info->enable)
 162                 return 0;
 163
 164         policy = this_dbs_info->cur_policy;
 165
 166         /*
 167          * we only care if our internally tracked freq moves outside
 168          * the 'valid' ranges of freqency available to us otherwise
 169          * we do not change it
 170         */
 171         if (this_dbs_info->requested_freq > policy->max
 172                         || this_dbs_info->requested_freq < policy->min)
 173                 this_dbs_info->requested_freq = freq->new;
 174
 175         return 0;
 176 }
 177
 178 static struct notifier_block dbs_cpufreq_notifier_block = {
 179         .notifier_call = dbs_cpufreq_notifier
 180 };
 181
 182 /************************** sysfs interface ************************/
 183 static ssize_t show_sampling_rate_max(struct cpufreq_policy *policy, char *buf)
 184 {
 185         static int print_once;
 186
 187         if (!print_once) {
 188                 printk(KERN_INFO "CPUFREQ: conservative sampling_rate_max "
 189                        "sysfs file is deprecated - used by: %s\n",
 190                        current->comm);
 191                 print_once = 1;
 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         static int print_once;
 199
 200         if (!print_once) {
 201                 printk(KERN_INFO "CPUFREQ: conservative sampling_rate_max "
 202                        "sysfs file is deprecated - used by: %s\n", current->comm);
 203                 print_once = 1;
 204         }
 205         return sprintf(buf, "%u\n", MIN_SAMPLING_RATE);
 206 }
 207
 208 #define define_one_ro(_name)            \
 209 static struct freq_attr _name =         \
 210 __ATTR(_name, 0444, show_##_name, NULL)
 211
 212 define_one_ro(sampling_rate_max);
 213 define_one_ro(sampling_rate_min);
 214
 215 /* cpufreq_conservative Governor Tunables */
 216 #define show_one(file_name, object)                                     \
 217 static ssize_t show_##file_name                                         \
 218 (struct cpufreq_policy *unused, char *buf)                              \
 219 {                                                                       \
 220         return sprintf(buf, "%u\n", dbs_tuners_ins.object);             \
 221 }
 222 show_one(sampling_rate, sampling_rate);
 223 show_one(sampling_down_factor, sampling_down_factor);
 224 show_one(up_threshold, up_threshold);
 225 show_one(down_threshold, down_threshold);
 226 show_one(ignore_nice_load, ignore_nice);
 227 show_one(freq_step, freq_step);
 228
 229 static ssize_t store_sampling_down_factor(struct cpufreq_policy *unused,
 230                 const char *buf, size_t count)
 231 {
 232         unsigned int input;
 233         int ret;
 234         ret = sscanf(buf, "%u", &input);
 235
 236         if (ret != 1 || input > MAX_SAMPLING_DOWN_FACTOR || input < 1)
 237                 return -EINVAL;
 238
 239         mutex_lock(&dbs_mutex);
 240         dbs_tuners_ins.sampling_down_factor = input;
 241         mutex_unlock(&dbs_mutex);
 242
 243         return count;
 244 }
 245
 246 static ssize_t store_sampling_rate(struct cpufreq_policy *unused,
 247                 const char *buf, size_t count)
 248 {
 249         unsigned int input;
 250         int ret;
 251         ret = sscanf(buf, "%u", &input);
 252
 253         if (ret != 1)
 254                 return -EINVAL;
 255
 256         mutex_lock(&dbs_mutex);
 257         dbs_tuners_ins.sampling_rate = max(input, minimum_sampling_rate());
 258         mutex_unlock(&dbs_mutex);
 259
 260         return count;
 261 }
 262
 263 static ssize_t store_up_threshold(struct cpufreq_policy *unused,
 264                 const char *buf, size_t count)
 265 {
 266         unsigned int input;
 267         int ret;
 268         ret = sscanf(buf, "%u", &input);
 269
 270         mutex_lock(&dbs_mutex);
 271         if (ret != 1 || input > 100 ||
 272                         input <= dbs_tuners_ins.down_threshold) {
 273                 mutex_unlock(&dbs_mutex);
 274                 return -EINVAL;
 275         }
 276
 277         dbs_tuners_ins.up_threshold = input;
 278         mutex_unlock(&dbs_mutex);
 279
 280         return count;
 281 }
 282
 283 static ssize_t store_down_threshold(struct cpufreq_policy *unused,
 284                 const char *buf, size_t count)
 285 {
 286         unsigned int input;
 287         int ret;
 288         ret = sscanf(buf, "%u", &input);
 289
 290         mutex_lock(&dbs_mutex);
 291         /* cannot be lower than 11 otherwise freq will not fall */
 292         if (ret != 1 || input < 11 || input > 100 ||
 293                         input >= dbs_tuners_ins.up_threshold) {
 294                 mutex_unlock(&dbs_mutex);
 295                 return -EINVAL;
 296         }
 297
 298         dbs_tuners_ins.down_threshold = input;
 299         mutex_unlock(&dbs_mutex);
 300
 301         return count;
 302 }
 303
 304 static ssize_t store_ignore_nice_load(struct cpufreq_policy *policy,
 305                 const char *buf, size_t count)
 306 {
 307         unsigned int input;
 308         int ret;
 309
 310         unsigned int j;
 311
 312         ret = sscanf(buf, "%u", &input);
 313         if (ret != 1)
 314                 return -EINVAL;
 315
 316         if (input > 1)
 317                 input = 1;
 318
 319         mutex_lock(&dbs_mutex);
 320         if (input == dbs_tuners_ins.ignore_nice) { /* nothing to do */
 321                 mutex_unlock(&dbs_mutex);
 322                 return count;
 323         }
 324         dbs_tuners_ins.ignore_nice = input;
 325
 326         /* we need to re-evaluate prev_cpu_idle */
 327         for_each_online_cpu(j) {
 328                 struct cpu_dbs_info_s *dbs_info;
 329                 dbs_info = &per_cpu(cpu_dbs_info, j);
 330                 dbs_info->prev_cpu_idle = get_cpu_idle_time(j,
 331                                                 &dbs_info->prev_cpu_wall);
 332                 if (dbs_tuners_ins.ignore_nice)
 333                         dbs_info->prev_cpu_nice = kstat_cpu(j).cpustat.nice;
 334         }
 335         mutex_unlock(&dbs_mutex);
 336
 337         return count;
 338 }
 339
 340 static ssize_t store_freq_step(struct cpufreq_policy *policy,
 341                 const char *buf, size_t count)
 342 {
 343         unsigned int input;
 344         int ret;
 345         ret = sscanf(buf, "%u", &input);
 346
 347         if (ret != 1)
 348                 return -EINVAL;
 349
 350         if (input > 100)
 351                 input = 100;
 352
 353         /* no need to test here if freq_step is zero as the user might actually
 354          * want this, they would be crazy though :) */
 355         mutex_lock(&dbs_mutex);
 356         dbs_tuners_ins.freq_step = input;
 357         mutex_unlock(&dbs_mutex);
 358
 359         return count;
 360 }
 361
 362 #define define_one_rw(_name) \
 363 static struct freq_attr _name = \
 364 __ATTR(_name, 0644, show_##_name, store_##_name)
 365
 366 define_one_rw(sampling_rate);
 367 define_one_rw(sampling_down_factor);
 368 define_one_rw(up_threshold);
 369 define_one_rw(down_threshold);
 370 define_one_rw(ignore_nice_load);
 371 define_one_rw(freq_step);
 372
 373 static struct attribute *dbs_attributes[] = {
 374         &sampling_rate_max.attr,
 375         &sampling_rate_min.attr,
 376         &sampling_rate.attr,
 377         &sampling_down_factor.attr,
 378         &up_threshold.attr,
 379         &down_threshold.attr,
 380         &ignore_nice_load.attr,
 381         &freq_step.attr,
 382         NULL
 383 };
 384
 385 static struct attribute_group dbs_attr_group = {
 386         .attrs = dbs_attributes,
 387         .name = "conservative",
 388 };
 389
 390 /************************** sysfs end ************************/
 391
 392 static void dbs_check_cpu(struct cpu_dbs_info_s *this_dbs_info)
 393 {
 394         unsigned int load = 0;
 395         unsigned int freq_target;
 396
 397         struct cpufreq_policy *policy;
 398         unsigned int j;
 399
 400         policy = this_dbs_info->cur_policy;
 401
 402         /*
 403          * Every sampling_rate, we check, if current idle time is less
 404          * than 20% (default), then we try to increase frequency
 405          * Every sampling_rate*sampling_down_factor, we check, if current
 406          * idle time is more than 80%, then we try to decrease frequency
 407          *
 408          * Any frequency increase takes it to the maximum frequency.
 409          * Frequency reduction happens at minimum steps of
 410          * 5% (default) of maximum frequency
 411          */
 412
 413         /* Get Absolute Load */
 414         for_each_cpu(j, policy->cpus) {
 415                 struct cpu_dbs_info_s *j_dbs_info;
 416                 cputime64_t cur_wall_time, cur_idle_time;
 417                 unsigned int idle_time, wall_time;
 418
 419                 j_dbs_info = &per_cpu(cpu_dbs_info, j);
 420
 421                 cur_idle_time = get_cpu_idle_time(j, &cur_wall_time);
 422
 423                 wall_time = (unsigned int) cputime64_sub(cur_wall_time,
 424                                 j_dbs_info->prev_cpu_wall);
 425                 j_dbs_info->prev_cpu_wall = cur_wall_time;
 426
 427                 idle_time = (unsigned int) cputime64_sub(cur_idle_time,
 428                                 j_dbs_info->prev_cpu_idle);
 429                 j_dbs_info->prev_cpu_idle = cur_idle_time;
 430
 431                 if (dbs_tuners_ins.ignore_nice) {
 432                         cputime64_t cur_nice;
 433                         unsigned long cur_nice_jiffies;
 434
 435                         cur_nice = cputime64_sub(kstat_cpu(j).cpustat.nice,
 436                                          j_dbs_info->prev_cpu_nice);
 437                         /*
 438                          * Assumption: nice time between sampling periods will
 439                          * be less than 2^32 jiffies for 32 bit sys
 440                          */
 441                         cur_nice_jiffies = (unsigned long)
 442                                         cputime64_to_jiffies64(cur_nice);
 443
 444                         j_dbs_info->prev_cpu_nice = kstat_cpu(j).cpustat.nice;
 445                         idle_time += jiffies_to_usecs(cur_nice_jiffies);
 446                 }
 447
 448                 if (unlikely(!wall_time || wall_time < idle_time))
 449                         continue;
 450
 451                 load = 100 * (wall_time - idle_time) / wall_time;
 452         }
 453
 454         /*
 455          * break out if we 'cannot' reduce the speed as the user might
 456          * want freq_step to be zero
 457          */
 458         if (dbs_tuners_ins.freq_step == 0)
 459                 return;
 460
 461         /* Check for frequency increase */
 462         if (load > dbs_tuners_ins.up_threshold) {
 463                 this_dbs_info->down_skip = 0;
 464
 465                 /* if we are already at full speed then break out early */
 466                 if (this_dbs_info->requested_freq == policy->max)
 467                         return;
 468
 469                 freq_target = (dbs_tuners_ins.freq_step * policy->max) / 100;
 470
 471                 /* max freq cannot be less than 100. But who knows.... */
 472                 if (unlikely(freq_target == 0))
 473                         freq_target = 5;
 474
 475                 this_dbs_info->requested_freq += freq_target;
 476                 if (this_dbs_info->requested_freq > policy->max)
 477                         this_dbs_info->requested_freq = policy->max;
 478
 479                 __cpufreq_driver_target(policy, this_dbs_info->requested_freq,
 480                         CPUFREQ_RELATION_H);
 481                 return;
 482         }
 483
 484         /*
 485          * The optimal frequency is the frequency that is the lowest that
 486          * can support the current CPU usage without triggering the up
 487          * policy. To be safe, we focus 10 points under the threshold.
 488          */
 489         if (load < (dbs_tuners_ins.down_threshold - 10)) {
 490                 freq_target = (dbs_tuners_ins.freq_step * policy->max) / 100;
 491
 492                 this_dbs_info->requested_freq -= freq_target;
 493                 if (this_dbs_info->requested_freq < policy->min)
 494                         this_dbs_info->requested_freq = policy->min;
 495
 496                 /*
 497                  * if we cannot reduce the frequency anymore, break out early
 498                  */
 499                 if (policy->cur == policy->min)
 500                         return;
 501
 502                 __cpufreq_driver_target(policy, this_dbs_info->requested_freq,
 503                                 CPUFREQ_RELATION_H);
 504                 return;
 505         }
 506 }
 507
 508 static void do_dbs_timer(struct work_struct *work)
 509 {
 510         struct cpu_dbs_info_s *dbs_info =
 511                 container_of(work, struct cpu_dbs_info_s, work.work);
 512         unsigned int cpu = dbs_info->cpu;
 513
 514         /* We want all CPUs to do sampling nearly on same jiffy */
 515         int delay = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
 516
 517         delay -= jiffies % delay;
 518
 519         if (lock_policy_rwsem_write(cpu) < 0)
 520                 return;
 521
 522         if (!dbs_info->enable) {
 523                 unlock_policy_rwsem_write(cpu);
 524                 return;
 525         }
 526
 527         dbs_check_cpu(dbs_info);
 528
 529         queue_delayed_work_on(cpu, kconservative_wq, &dbs_info->work, delay);
 530         unlock_policy_rwsem_write(cpu);
 531 }
 532
 533 static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
 534 {
 535         /* We want all CPUs to do sampling nearly on same jiffy */
 536         int delay = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
 537         delay -= jiffies % delay;
 538
 539         dbs_info->enable = 1;
 540         INIT_DELAYED_WORK_DEFERRABLE(&dbs_info->work, do_dbs_timer);
 541         queue_delayed_work_on(dbs_info->cpu, kconservative_wq, &dbs_info->work,
 542                                 delay);
 543 }
 544
 545 static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
 546 {
 547         dbs_info->enable = 0;
 548         cancel_delayed_work_sync(&dbs_info->work);
 549 }
 550
 551 static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 552                                    unsigned int event)
 553 {
 554         unsigned int cpu = policy->cpu;
 555         struct cpu_dbs_info_s *this_dbs_info;
 556         unsigned int j;
 557         int rc;
 558
 559         this_dbs_info = &per_cpu(cpu_dbs_info, cpu);
 560
 561         switch (event) {
 562         case CPUFREQ_GOV_START:
 563                 if ((!cpu_online(cpu)) || (!policy->cur))
 564                         return -EINVAL;
 565
 566                 if (this_dbs_info->enable) /* Already enabled */
 567                         break;
 568
 569                 mutex_lock(&dbs_mutex);
 570
 571                 rc = sysfs_create_group(&policy->kobj, &dbs_attr_group);
 572                 if (rc) {
 573                         mutex_unlock(&dbs_mutex);
 574                         return rc;
 575                 }
 576
 577                 for_each_cpu(j, policy->cpus) {
 578                         struct cpu_dbs_info_s *j_dbs_info;
 579                         j_dbs_info = &per_cpu(cpu_dbs_info, j);
 580                         j_dbs_info->cur_policy = policy;
 581
 582                         j_dbs_info->prev_cpu_idle = get_cpu_idle_time(j,
 583                                                 &j_dbs_info->prev_cpu_wall);
 584                         if (dbs_tuners_ins.ignore_nice) {
 585                                 j_dbs_info->prev_cpu_nice =
 586                                                 kstat_cpu(j).cpustat.nice;
 587                         }
 588                 }
 589                 this_dbs_info->down_skip = 0;
 590                 this_dbs_info->requested_freq = policy->cur;
 591
 592                 dbs_enable++;
 593                 /*
 594                  * Start the timerschedule work, when this governor
 595                  * is used for first time
 596                  */
 597                 if (dbs_enable == 1) {
 598                         unsigned int latency;
 599                         /* policy latency is in nS. Convert it to uS first */
 600                         latency = policy->cpuinfo.transition_latency / 1000;
 601                         if (latency == 0)
 602                                 latency = 1;
 603
 604                         def_sampling_rate =
 605                                 max(latency * LATENCY_MULTIPLIER,
 606                                     MIN_STAT_SAMPLING_RATE);
 607
 608                         dbs_tuners_ins.sampling_rate = def_sampling_rate;
 609
 610                         cpufreq_register_notifier(
 611                                         &dbs_cpufreq_notifier_block,
 612                                         CPUFREQ_TRANSITION_NOTIFIER);
 613                 }
 614                 dbs_timer_init(this_dbs_info);
 615
 616                 mutex_unlock(&dbs_mutex);
 617
 618                 break;
 619
 620         case CPUFREQ_GOV_STOP:
 621                 mutex_lock(&dbs_mutex);
 622                 dbs_timer_exit(this_dbs_info);
 623                 sysfs_remove_group(&policy->kobj, &dbs_attr_group);
 624                 dbs_enable--;
 625
 626                 /*
 627                  * Stop the timerschedule work, when this governor
 628                  * is used for first time
 629                  */
 630                 if (dbs_enable == 0)
 631                         cpufreq_unregister_notifier(
 632                                         &dbs_cpufreq_notifier_block,
 633                                         CPUFREQ_TRANSITION_NOTIFIER);
 634
 635                 mutex_unlock(&dbs_mutex);
 636
 637                 break;
 638
 639         case CPUFREQ_GOV_LIMITS:
 640                 mutex_lock(&dbs_mutex);
 641                 if (policy->max < this_dbs_info->cur_policy->cur)
 642                         __cpufreq_driver_target(
 643                                         this_dbs_info->cur_policy,
 644                                         policy->max, CPUFREQ_RELATION_H);
 645                 else if (policy->min > this_dbs_info->cur_policy->cur)
 646                         __cpufreq_driver_target(
 647                                         this_dbs_info->cur_policy,
 648                                         policy->min, CPUFREQ_RELATION_L);
 649                 mutex_unlock(&dbs_mutex);
 650
 651                 break;
 652         }
 653         return 0;
 654 }
 655
 656 #ifndef CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE
 657 static
 658 #endif
 659 struct cpufreq_governor cpufreq_gov_conservative = {
 660         .name                   = "conservative",
 661         .governor               = cpufreq_governor_dbs,
 662         .max_transition_latency = TRANSITION_LATENCY_LIMIT,
 663         .owner                  = THIS_MODULE,
 664 };
 665
 666 static int __init cpufreq_gov_dbs_init(void)
 667 {
 668         int err;
 669
 670         kconservative_wq = create_workqueue("kconservative");
 671         if (!kconservative_wq) {
 672                 printk(KERN_ERR "Creation of kconservative failed\n");
 673                 return -EFAULT;
 674         }
 675
 676         err = cpufreq_register_governor(&cpufreq_gov_conservative);
 677         if (err)
 678                 destroy_workqueue(kconservative_wq);
 679
 680         return err;
 681 }
 682
 683 static void __exit cpufreq_gov_dbs_exit(void)
 684 {
 685         cpufreq_unregister_governor(&cpufreq_gov_conservative);
 686         destroy_workqueue(kconservative_wq);
 687 }
 688
 689
 690 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
 691 MODULE_DESCRIPTION("'cpufreq_conservative' - A dynamic cpufreq governor for "
 692                 "Low Latency Frequency Transition capable processors "
 693                 "optimised for use in a battery environment");
 694 MODULE_LICENSE("GPL");
 695
 696 #ifdef CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE
 697 fs_initcall(cpufreq_gov_dbs_init);
 698 #else
 699 module_init(cpufreq_gov_dbs_init);
 700 #endif
 701 module_exit(cpufreq_gov_dbs_exit);