arch/i386/kernel/tsc.c

   1 /*
   2  * This code largely moved from arch/i386/kernel/timer/timer_tsc.c
   3  * which was originally moved from arch/i386/kernel/time.c.
   4  * See comments there for proper credits.
   5  */
   6
   7 #include <linux/clocksource.h>
   8 #include <linux/workqueue.h>
   9 #include <linux/cpufreq.h>
  10 #include <linux/jiffies.h>
  11 #include <linux/init.h>
  12 #include <linux/dmi.h>
  13
  14 #include <asm/delay.h>
  15 #include <asm/tsc.h>
  16 #include <asm/delay.h>
  17 #include <asm/io.h>
  18
  19 #include "mach_timer.h"
  20
  21 /*
  22  * On some systems the TSC frequency does not
  23  * change with the cpu frequency. So we need
  24  * an extra value to store the TSC freq
  25  */
  26 unsigned int tsc_khz;
  27
  28 int tsc_disable __cpuinitdata = 0;
  29
  30 #ifdef CONFIG_X86_TSC
  31 static int __init tsc_setup(char *str)
  32 {
  33         printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
  34                                 "cannot disable TSC.\n");
  35         return 1;
  36 }
  37 #else
  38 /*
  39  * disable flag for tsc. Takes effect by clearing the TSC cpu flag
  40  * in cpu/common.c
  41  */
  42 static int __init tsc_setup(char *str)
  43 {
  44         tsc_disable = 1;
  45
  46         return 1;
  47 }
  48 #endif
  49
  50 __setup("notsc", tsc_setup);
  51
  52 /*
  53  * code to mark and check if the TSC is unstable
  54  * due to cpufreq or due to unsynced TSCs
  55  */
  56 static int tsc_unstable;
  57
  58 static inline int check_tsc_unstable(void)
  59 {
  60         return tsc_unstable;
  61 }
  62
  63 void mark_tsc_unstable(void)
  64 {
  65         tsc_unstable = 1;
  66 }
  67 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
  68
  69 /* Accellerators for sched_clock()
  70  * convert from cycles(64bits) => nanoseconds (64bits)
  71  *  basic equation:
  72  *              ns = cycles / (freq / ns_per_sec)
  73  *              ns = cycles * (ns_per_sec / freq)
  74  *              ns = cycles * (10^9 / (cpu_khz * 10^3))
  75  *              ns = cycles * (10^6 / cpu_khz)
  76  *
  77  *      Then we use scaling math (suggested by george@mvista.com) to get:
  78  *              ns = cycles * (10^6 * SC / cpu_khz) / SC
  79  *              ns = cycles * cyc2ns_scale / SC
  80  *
  81  *      And since SC is a constant power of two, we can convert the div
  82  *  into a shift.
  83  *
  84  *  We can use khz divisor instead of mhz to keep a better percision, since
  85  *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
  86  *  (mathieu.desnoyers@polymtl.ca)
  87  *
  88  *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
  89  */
  90 static unsigned long cyc2ns_scale __read_mostly;
  91
  92 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
  93
  94 static inline void set_cyc2ns_scale(unsigned long cpu_khz)
  95 {
  96         cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
  97 }
  98
  99 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
 100 {
 101         return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
 102 }
 103
 104 /*
 105  * Scheduler clock - returns current time in nanosec units.
 106  */
 107 unsigned long long sched_clock(void)
 108 {
 109         unsigned long long this_offset;
 110
 111         /*
 112          * in the NUMA case we dont use the TSC as they are not
 113          * synchronized across all CPUs.
 114          */
 115 #ifndef CONFIG_NUMA
 116         if (!cpu_khz || check_tsc_unstable())
 117 #endif
 118                 /* no locking but a rare wrong value is not a big deal */
 119                 return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
 120
 121         /* read the Time Stamp Counter: */
 122         rdtscll(this_offset);
 123
 124         /* return the value in ns */
 125         return cycles_2_ns(this_offset);
 126 }
 127
 128 static unsigned long calculate_cpu_khz(void)
 129 {
 130         unsigned long long start, end;
 131         unsigned long count;
 132         u64 delta64;
 133         int i;
 134         unsigned long flags;
 135
 136         local_irq_save(flags);
 137
 138         /* run 3 times to ensure the cache is warm */
 139         for (i = 0; i < 3; i++) {
 140                 mach_prepare_counter();
 141                 rdtscll(start);
 142                 mach_countup(&count);
 143                 rdtscll(end);
 144         }
 145         /*
 146          * Error: ECTCNEVERSET
 147          * The CTC wasn't reliable: we got a hit on the very first read,
 148          * or the CPU was so fast/slow that the quotient wouldn't fit in
 149          * 32 bits..
 150          */
 151         if (count <= 1)
 152                 goto err;
 153
 154         delta64 = end - start;
 155
 156         /* cpu freq too fast: */
 157         if (delta64 > (1ULL<<32))
 158                 goto err;
 159
 160         /* cpu freq too slow: */
 161         if (delta64 <= CALIBRATE_TIME_MSEC)
 162                 goto err;
 163
 164         delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
 165         do_div(delta64,CALIBRATE_TIME_MSEC);
 166
 167         local_irq_restore(flags);
 168         return (unsigned long)delta64;
 169 err:
 170         local_irq_restore(flags);
 171         return 0;
 172 }
 173
 174 int recalibrate_cpu_khz(void)
 175 {
 176 #ifndef CONFIG_SMP
 177         unsigned long cpu_khz_old = cpu_khz;
 178
 179         if (cpu_has_tsc) {
 180                 cpu_khz = calculate_cpu_khz();
 181                 tsc_khz = cpu_khz;
 182                 cpu_data[0].loops_per_jiffy =
 183                         cpufreq_scale(cpu_data[0].loops_per_jiffy,
 184                                         cpu_khz_old, cpu_khz);
 185                 return 0;
 186         } else
 187                 return -ENODEV;
 188 #else
 189         return -ENODEV;
 190 #endif
 191 }
 192
 193 EXPORT_SYMBOL(recalibrate_cpu_khz);
 194
 195 void tsc_init(void)
 196 {
 197         if (!cpu_has_tsc || tsc_disable)
 198                 return;
 199
 200         cpu_khz = calculate_cpu_khz();
 201         tsc_khz = cpu_khz;
 202
 203         if (!cpu_khz)
 204                 return;
 205
 206         printk("Detected %lu.%03lu MHz processor.\n",
 207                                 (unsigned long)cpu_khz / 1000,
 208                                 (unsigned long)cpu_khz % 1000);
 209
 210         set_cyc2ns_scale(cpu_khz);
 211         use_tsc_delay();
 212 }
 213
 214 #ifdef CONFIG_CPU_FREQ
 215
 216 static unsigned int cpufreq_delayed_issched = 0;
 217 static unsigned int cpufreq_init = 0;
 218 static struct work_struct cpufreq_delayed_get_work;
 219
 220 static void handle_cpufreq_delayed_get(void *v)
 221 {
 222         unsigned int cpu;
 223
 224         for_each_online_cpu(cpu)
 225                 cpufreq_get(cpu);
 226
 227         cpufreq_delayed_issched = 0;
 228 }
 229
 230 /*
 231  * if we notice cpufreq oddness, schedule a call to cpufreq_get() as it tries
 232  * to verify the CPU frequency the timing core thinks the CPU is running
 233  * at is still correct.
 234  */
 235 static inline void cpufreq_delayed_get(void)
 236 {
 237         if (cpufreq_init && !cpufreq_delayed_issched) {
 238                 cpufreq_delayed_issched = 1;
 239                 printk(KERN_DEBUG "Checking if CPU frequency changed.\n");
 240                 schedule_work(&cpufreq_delayed_get_work);
 241         }
 242 }
 243
 244 /*
 245  * if the CPU frequency is scaled, TSC-based delays will need a different
 246  * loops_per_jiffy value to function properly.
 247  */
 248 static unsigned int ref_freq = 0;
 249 static unsigned long loops_per_jiffy_ref = 0;
 250 static unsigned long cpu_khz_ref = 0;
 251
 252 static int
 253 time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
 254 {
 255         struct cpufreq_freqs *freq = data;
 256
 257         if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
 258                 write_seqlock_irq(&xtime_lock);
 259
 260         if (!ref_freq) {
 261                 if (!freq->old){
 262                         ref_freq = freq->new;
 263                         goto end;
 264                 }
 265                 ref_freq = freq->old;
 266                 loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy;
 267                 cpu_khz_ref = cpu_khz;
 268         }
 269
 270         if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
 271             (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
 272             (val == CPUFREQ_RESUMECHANGE)) {
 273                 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
 274                         cpu_data[freq->cpu].loops_per_jiffy =
 275                                 cpufreq_scale(loops_per_jiffy_ref,
 276                                                 ref_freq, freq->new);
 277
 278                 if (cpu_khz) {
 279
 280                         if (num_online_cpus() == 1)
 281                                 cpu_khz = cpufreq_scale(cpu_khz_ref,
 282                                                 ref_freq, freq->new);
 283                         if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
 284                                 tsc_khz = cpu_khz;
 285                                 set_cyc2ns_scale(cpu_khz);
 286                                 /*
 287                                  * TSC based sched_clock turns
 288                                  * to junk w/ cpufreq
 289                                  */
 290                                 mark_tsc_unstable();
 291                         }
 292                 }
 293         }
 294 end:
 295         if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
 296                 write_sequnlock_irq(&xtime_lock);
 297
 298         return 0;
 299 }
 300
 301 static struct notifier_block time_cpufreq_notifier_block = {
 302         .notifier_call  = time_cpufreq_notifier
 303 };
 304
 305 static int __init cpufreq_tsc(void)
 306 {
 307         int ret;
 308
 309         INIT_WORK(&cpufreq_delayed_get_work, handle_cpufreq_delayed_get, NULL);
 310         ret = cpufreq_register_notifier(&time_cpufreq_notifier_block,
 311                                         CPUFREQ_TRANSITION_NOTIFIER);
 312         if (!ret)
 313                 cpufreq_init = 1;
 314
 315         return ret;
 316 }
 317
 318 core_initcall(cpufreq_tsc);
 319
 320 #endif
 321
 322 /* clock source code */
 323
 324 static unsigned long current_tsc_khz = 0;
 325 static int tsc_update_callback(void);
 326
 327 static cycle_t read_tsc(void)
 328 {
 329         cycle_t ret;
 330
 331         rdtscll(ret);
 332
 333         return ret;
 334 }
 335
 336 static struct clocksource clocksource_tsc = {
 337         .name                   = "tsc",
 338         .rating                 = 300,
 339         .read                   = read_tsc,
 340         .mask                   = CLOCKSOURCE_MASK(64),
 341         .mult                   = 0, /* to be set */
 342         .shift                  = 22,
 343         .update_callback        = tsc_update_callback,
 344         .is_continuous          = 1,
 345 };
 346
 347 static int tsc_update_callback(void)
 348 {
 349         int change = 0;
 350
 351         /* check to see if we should switch to the safe clocksource: */
 352         if (clocksource_tsc.rating != 50 && check_tsc_unstable()) {
 353                 clocksource_tsc.rating = 50;
 354                 clocksource_reselect();
 355                 change = 1;
 356         }
 357
 358         /* only update if tsc_khz has changed: */
 359         if (current_tsc_khz != tsc_khz) {
 360                 current_tsc_khz = tsc_khz;
 361                 clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
 362                                                         clocksource_tsc.shift);
 363                 change = 1;
 364         }
 365
 366         return change;
 367 }
 368
 369 static int __init dmi_mark_tsc_unstable(struct dmi_system_id *d)
 370 {
 371         printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
 372                        d->ident);
 373         mark_tsc_unstable();
 374         return 0;
 375 }
 376
 377 /* List of systems that have known TSC problems */
 378 static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
 379         {
 380          .callback = dmi_mark_tsc_unstable,
 381          .ident = "IBM Thinkpad 380XD",
 382          .matches = {
 383                      DMI_MATCH(DMI_BOARD_VENDOR, "IBM"),
 384                      DMI_MATCH(DMI_BOARD_NAME, "2635FA0"),
 385                      },
 386          },
 387          {}
 388 };
 389
 390 #define TSC_FREQ_CHECK_INTERVAL (10*MSEC_PER_SEC) /* 10sec in MS */
 391 static struct timer_list verify_tsc_freq_timer;
 392
 393 /* XXX - Probably should add locking */
 394 static void verify_tsc_freq(unsigned long unused)
 395 {
 396         static u64 last_tsc;
 397         static unsigned long last_jiffies;
 398
 399         u64 now_tsc, interval_tsc;
 400         unsigned long now_jiffies, interval_jiffies;
 401
 402
 403         if (check_tsc_unstable())
 404                 return;
 405
 406         rdtscll(now_tsc);
 407         now_jiffies = jiffies;
 408
 409         if (!last_jiffies) {
 410                 goto out;
 411         }
 412
 413         interval_jiffies = now_jiffies - last_jiffies;
 414         interval_tsc = now_tsc - last_tsc;
 415         interval_tsc *= HZ;
 416         do_div(interval_tsc, cpu_khz*1000);
 417
 418         if (interval_tsc < (interval_jiffies * 3 / 4)) {
 419                 printk("TSC appears to be running slowly. "
 420                         "Marking it as unstable\n");
 421                 mark_tsc_unstable();
 422                 return;
 423         }
 424
 425 out:
 426         last_tsc = now_tsc;
 427         last_jiffies = now_jiffies;
 428         /* set us up to go off on the next interval: */
 429         mod_timer(&verify_tsc_freq_timer,
 430                 jiffies + msecs_to_jiffies(TSC_FREQ_CHECK_INTERVAL));
 431 }
 432
 433 /*
 434  * Make an educated guess if the TSC is trustworthy and synchronized
 435  * over all CPUs.
 436  */
 437 static __init int unsynchronized_tsc(void)
 438 {
 439         /*
 440          * Intel systems are normally all synchronized.
 441          * Exceptions must mark TSC as unstable:
 442          */
 443         if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
 444                 return 0;
 445
 446         /* assume multi socket systems are not synchronized: */
 447         return num_possible_cpus() > 1;
 448 }
 449
 450 static int __init init_tsc_clocksource(void)
 451 {
 452
 453         if (cpu_has_tsc && tsc_khz && !tsc_disable) {
 454                 /* check blacklist */
 455                 dmi_check_system(bad_tsc_dmi_table);
 456
 457                 if (unsynchronized_tsc()) /* mark unstable if unsynced */
 458                         mark_tsc_unstable();
 459                 current_tsc_khz = tsc_khz;
 460                 clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
 461                                                         clocksource_tsc.shift);
 462                 /* lower the rating if we already know its unstable: */
 463                 if (check_tsc_unstable())
 464                         clocksource_tsc.rating = 50;
 465
 466                 init_timer(&verify_tsc_freq_timer);
 467                 verify_tsc_freq_timer.function = verify_tsc_freq;
 468                 verify_tsc_freq_timer.expires =
 469                         jiffies + msecs_to_jiffies(TSC_FREQ_CHECK_INTERVAL);
 470                 add_timer(&verify_tsc_freq_timer);
 471
 472                 return clocksource_register(&clocksource_tsc);
 473         }
 474
 475         return 0;
 476 }
 477
 478 module_init(init_tsc_clocksource);