arch/x86/kernel/tsc_32.c

   1 #include <linux/sched.h>
   2 #include <linux/clocksource.h>
   3 #include <linux/workqueue.h>
   4 #include <linux/cpufreq.h>
   5 #include <linux/jiffies.h>
   6 #include <linux/init.h>
   7 #include <linux/dmi.h>
   8 #include <linux/percpu.h>
   9
  10 #include <asm/delay.h>
  11 #include <asm/tsc.h>
  12 #include <asm/io.h>
  13 #include <asm/timer.h>
  14
  15 #include "mach_timer.h"
  16
  17 static int tsc_disabled;
  18
  19 /*
  20  * On some systems the TSC frequency does not
  21  * change with the cpu frequency. So we need
  22  * an extra value to store the TSC freq
  23  */
  24 unsigned int tsc_khz;
  25 EXPORT_SYMBOL_GPL(tsc_khz);
  26
  27 #ifdef CONFIG_X86_TSC
  28 static int __init tsc_setup(char *str)
  29 {
  30         printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
  31                "cannot disable TSC completely.\n");
  32         tsc_disabled = 1;
  33         return 1;
  34 }
  35 #else
  36 /*
  37  * disable flag for tsc. Takes effect by clearing the TSC cpu flag
  38  * in cpu/common.c
  39  */
  40 static int __init tsc_setup(char *str)
  41 {
  42         setup_clear_cpu_cap(X86_FEATURE_TSC);
  43         return 1;
  44 }
  45 #endif
  46
  47 __setup("notsc", tsc_setup);
  48
  49 /*
  50  * code to mark and check if the TSC is unstable
  51  * due to cpufreq or due to unsynced TSCs
  52  */
  53 static int tsc_unstable;
  54
  55 int check_tsc_unstable(void)
  56 {
  57         return tsc_unstable;
  58 }
  59 EXPORT_SYMBOL_GPL(check_tsc_unstable);
  60
  61 /* Accelerators for sched_clock()
  62  * convert from cycles(64bits) => nanoseconds (64bits)
  63  *  basic equation:
  64  *              ns = cycles / (freq / ns_per_sec)
  65  *              ns = cycles * (ns_per_sec / freq)
  66  *              ns = cycles * (10^9 / (cpu_khz * 10^3))
  67  *              ns = cycles * (10^6 / cpu_khz)
  68  *
  69  *      Then we use scaling math (suggested by george@mvista.com) to get:
  70  *              ns = cycles * (10^6 * SC / cpu_khz) / SC
  71  *              ns = cycles * cyc2ns_scale / SC
  72  *
  73  *      And since SC is a constant power of two, we can convert the div
  74  *  into a shift.
  75  *
  76  *  We can use khz divisor instead of mhz to keep a better precision, since
  77  *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
  78  *  (mathieu.desnoyers@polymtl.ca)
  79  *
  80  *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
  81  */
  82
  83 DEFINE_PER_CPU(unsigned long, cyc2ns);
  84
  85 static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
  86 {
  87         unsigned long long tsc_now, ns_now;
  88         unsigned long flags, *scale;
  89
  90         local_irq_save(flags);
  91         sched_clock_idle_sleep_event();
  92
  93         scale = &per_cpu(cyc2ns, cpu);
  94
  95         rdtscll(tsc_now);
  96         ns_now = __cycles_2_ns(tsc_now);
  97
  98         if (cpu_khz)
  99                 *scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
 100
 101         /*
 102          * Start smoothly with the new frequency:
 103          */
 104         sched_clock_idle_wakeup_event(0);
 105         local_irq_restore(flags);
 106 }
 107
 108 /*
 109  * Scheduler clock - returns current time in nanosec units.
 110  */
 111 unsigned long long native_sched_clock(void)
 112 {
 113         unsigned long long this_offset;
 114
 115         /*
 116          * Fall back to jiffies if there's no TSC available:
 117          * ( But note that we still use it if the TSC is marked
 118          *   unstable. We do this because unlike Time Of Day,
 119          *   the scheduler clock tolerates small errors and it's
 120          *   very important for it to be as fast as the platform
 121          *   can achive it. )
 122          */
 123         if (unlikely(tsc_disabled))
 124                 /* No locking but a rare wrong value is not a big deal: */
 125                 return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
 126
 127         /* read the Time Stamp Counter: */
 128         rdtscll(this_offset);
 129
 130         /* return the value in ns */
 131         return cycles_2_ns(this_offset);
 132 }
 133
 134 /* We need to define a real function for sched_clock, to override the
 135    weak default version */
 136 #ifdef CONFIG_PARAVIRT
 137 unsigned long long sched_clock(void)
 138 {
 139         return paravirt_sched_clock();
 140 }
 141 #else
 142 unsigned long long sched_clock(void)
 143         __attribute__((alias("native_sched_clock")));
 144 #endif
 145
 146 unsigned long native_calculate_cpu_khz(void)
 147 {
 148         unsigned long long start, end;
 149         unsigned long count;
 150         u64 delta64 = (u64)ULLONG_MAX;
 151         int i;
 152         unsigned long flags;
 153
 154         local_irq_save(flags);
 155
 156         /* run 3 times to ensure the cache is warm and to get an accurate reading */
 157         for (i = 0; i < 3; i++) {
 158                 mach_prepare_counter();
 159                 rdtscll(start);
 160                 mach_countup(&count);
 161                 rdtscll(end);
 162
 163                 /*
 164                  * Error: ECTCNEVERSET
 165                  * The CTC wasn't reliable: we got a hit on the very first read,
 166                  * or the CPU was so fast/slow that the quotient wouldn't fit in
 167                  * 32 bits..
 168                  */
 169                 if (count <= 1)
 170                         continue;
 171
 172                 /* cpu freq too slow: */
 173                 if ((end - start) <= CALIBRATE_TIME_MSEC)
 174                         continue;
 175
 176                 /*
 177                  * We want the minimum time of all runs in case one of them
 178                  * is inaccurate due to SMI or other delay
 179                  */
 180                 delta64 = min(delta64, (end - start));
 181         }
 182
 183         /* cpu freq too fast (or every run was bad): */
 184         if (delta64 > (1ULL<<32))
 185                 goto err;
 186
 187         delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
 188         do_div(delta64,CALIBRATE_TIME_MSEC);
 189
 190         local_irq_restore(flags);
 191         return (unsigned long)delta64;
 192 err:
 193         local_irq_restore(flags);
 194         return 0;
 195 }
 196
 197 int recalibrate_cpu_khz(void)
 198 {
 199 #ifndef CONFIG_SMP
 200         unsigned long cpu_khz_old = cpu_khz;
 201
 202         if (cpu_has_tsc) {
 203                 cpu_khz = calculate_cpu_khz();
 204                 tsc_khz = cpu_khz;
 205                 cpu_data(0).loops_per_jiffy =
 206                         cpufreq_scale(cpu_data(0).loops_per_jiffy,
 207                                         cpu_khz_old, cpu_khz);
 208                 return 0;
 209         } else
 210                 return -ENODEV;
 211 #else
 212         return -ENODEV;
 213 #endif
 214 }
 215
 216 EXPORT_SYMBOL(recalibrate_cpu_khz);
 217
 218 #ifdef CONFIG_CPU_FREQ
 219
 220 /*
 221  * if the CPU frequency is scaled, TSC-based delays will need a different
 222  * loops_per_jiffy value to function properly.
 223  */
 224 static unsigned int ref_freq;
 225 static unsigned long loops_per_jiffy_ref;
 226 static unsigned long cpu_khz_ref;
 227
 228 static int
 229 time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
 230 {
 231         struct cpufreq_freqs *freq = data;
 232
 233         if (!ref_freq) {
 234                 if (!freq->old){
 235                         ref_freq = freq->new;
 236                         return 0;
 237                 }
 238                 ref_freq = freq->old;
 239                 loops_per_jiffy_ref = cpu_data(freq->cpu).loops_per_jiffy;
 240                 cpu_khz_ref = cpu_khz;
 241         }
 242
 243         if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
 244             (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
 245             (val == CPUFREQ_RESUMECHANGE)) {
 246                 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
 247                         cpu_data(freq->cpu).loops_per_jiffy =
 248                                 cpufreq_scale(loops_per_jiffy_ref,
 249                                                 ref_freq, freq->new);
 250
 251                 if (cpu_khz) {
 252
 253                         if (num_online_cpus() == 1)
 254                                 cpu_khz = cpufreq_scale(cpu_khz_ref,
 255                                                 ref_freq, freq->new);
 256                         if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
 257                                 tsc_khz = cpu_khz;
 258                                 set_cyc2ns_scale(cpu_khz, freq->cpu);
 259                                 /*
 260                                  * TSC based sched_clock turns
 261                                  * to junk w/ cpufreq
 262                                  */
 263                                 mark_tsc_unstable("cpufreq changes");
 264                         }
 265                 }
 266         }
 267
 268         return 0;
 269 }
 270
 271 static struct notifier_block time_cpufreq_notifier_block = {
 272         .notifier_call  = time_cpufreq_notifier
 273 };
 274
 275 static int __init cpufreq_tsc(void)
 276 {
 277         return cpufreq_register_notifier(&time_cpufreq_notifier_block,
 278                                          CPUFREQ_TRANSITION_NOTIFIER);
 279 }
 280 core_initcall(cpufreq_tsc);
 281
 282 #endif
 283
 284 /* clock source code */
 285
 286 static struct clocksource clocksource_tsc;
 287
 288 /*
 289  * We compare the TSC to the cycle_last value in the clocksource
 290  * structure to avoid a nasty time-warp issue. This can be observed in
 291  * a very small window right after one CPU updated cycle_last under
 292  * xtime lock and the other CPU reads a TSC value which is smaller
 293  * than the cycle_last reference value due to a TSC which is slighty
 294  * behind. This delta is nowhere else observable, but in that case it
 295  * results in a forward time jump in the range of hours due to the
 296  * unsigned delta calculation of the time keeping core code, which is
 297  * necessary to support wrapping clocksources like pm timer.
 298  */
 299 static cycle_t read_tsc(void)
 300 {
 301         cycle_t ret;
 302
 303         rdtscll(ret);
 304
 305         return ret >= clocksource_tsc.cycle_last ?
 306                 ret : clocksource_tsc.cycle_last;
 307 }
 308
 309 static struct clocksource clocksource_tsc = {
 310         .name                   = "tsc",
 311         .rating                 = 300,
 312         .read                   = read_tsc,
 313         .mask                   = CLOCKSOURCE_MASK(64),
 314         .mult                   = 0, /* to be set */
 315         .shift                  = 22,
 316         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
 317                                   CLOCK_SOURCE_MUST_VERIFY,
 318 };
 319
 320 void mark_tsc_unstable(char *reason)
 321 {
 322         if (!tsc_unstable) {
 323                 tsc_unstable = 1;
 324                 printk("Marking TSC unstable due to: %s.\n", reason);
 325                 /* Can be called before registration */
 326                 if (clocksource_tsc.mult)
 327                         clocksource_change_rating(&clocksource_tsc, 0);
 328                 else
 329                         clocksource_tsc.rating = 0;
 330         }
 331 }
 332 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
 333
 334 static int __init dmi_mark_tsc_unstable(const struct dmi_system_id *d)
 335 {
 336         printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
 337                d->ident);
 338         tsc_unstable = 1;
 339         return 0;
 340 }
 341
 342 /* List of systems that have known TSC problems */
 343 static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
 344         {
 345          .callback = dmi_mark_tsc_unstable,
 346          .ident = "IBM Thinkpad 380XD",
 347          .matches = {
 348                      DMI_MATCH(DMI_BOARD_VENDOR, "IBM"),
 349                      DMI_MATCH(DMI_BOARD_NAME, "2635FA0"),
 350                      },
 351          },
 352          {}
 353 };
 354
 355 /*
 356  * Make an educated guess if the TSC is trustworthy and synchronized
 357  * over all CPUs.
 358  */
 359 __cpuinit int unsynchronized_tsc(void)
 360 {
 361         if (!cpu_has_tsc || tsc_unstable)
 362                 return 1;
 363
 364         /* Anything with constant TSC should be synchronized */
 365         if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
 366                 return 0;
 367
 368         /*
 369          * Intel systems are normally all synchronized.
 370          * Exceptions must mark TSC as unstable:
 371          */
 372         if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
 373                 /* assume multi socket systems are not synchronized: */
 374                 if (num_possible_cpus() > 1)
 375                         tsc_unstable = 1;
 376         }
 377         return tsc_unstable;
 378 }
 379
 380 /*
 381  * Geode_LX - the OLPC CPU has a possibly a very reliable TSC
 382  */
 383 #ifdef CONFIG_MGEODE_LX
 384 /* RTSC counts during suspend */
 385 #define RTSC_SUSP 0x100
 386
 387 static void __init check_geode_tsc_reliable(void)
 388 {
 389         unsigned long res_low, res_high;
 390
 391         rdmsr_safe(MSR_GEODE_BUSCONT_CONF0, &res_low, &res_high);
 392         if (res_low & RTSC_SUSP)
 393                 clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
 394 }
 395 #else
 396 static inline void check_geode_tsc_reliable(void) { }
 397 #endif
 398
 399
 400 void __init tsc_init(void)
 401 {
 402         int cpu;
 403
 404         if (!cpu_has_tsc || tsc_disabled) {
 405                 /* Disable the TSC in case of !cpu_has_tsc */
 406                 tsc_disabled = 1;
 407                 return;
 408         }
 409
 410         cpu_khz = calculate_cpu_khz();
 411         tsc_khz = cpu_khz;
 412
 413         if (!cpu_khz) {
 414                 mark_tsc_unstable("could not calculate TSC khz");
 415                 /*
 416                  * We need to disable the TSC completely in this case
 417                  * to prevent sched_clock() from using it.
 418                  */
 419                 tsc_disabled = 1;
 420                 return;
 421         }
 422
 423         printk("Detected %lu.%03lu MHz processor.\n",
 424                                 (unsigned long)cpu_khz / 1000,
 425                                 (unsigned long)cpu_khz % 1000);
 426
 427         /*
 428          * Secondary CPUs do not run through tsc_init(), so set up
 429          * all the scale factors for all CPUs, assuming the same
 430          * speed as the bootup CPU. (cpufreq notifiers will fix this
 431          * up if their speed diverges)
 432          */
 433         for_each_possible_cpu(cpu)
 434                 set_cyc2ns_scale(cpu_khz, cpu);
 435
 436         use_tsc_delay();
 437
 438         /* Check and install the TSC clocksource */
 439         dmi_check_system(bad_tsc_dmi_table);
 440
 441         unsynchronized_tsc();
 442         check_geode_tsc_reliable();
 443         clocksource_tsc.mult = clocksource_khz2mult(tsc_khz,
 444                                                     clocksource_tsc.shift);
 445         /* lower the rating if we already know its unstable: */
 446         if (check_tsc_unstable()) {
 447                 clocksource_tsc.rating = 0;
 448                 clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
 449         }
 450         clocksource_register(&clocksource_tsc);
 451 }