arch/x86/kernel/tsc_32.c

   1 #include <linux/sched.h>
   2 #include <linux/clocksource.h>
   3 #include <linux/workqueue.h>
   4 #include <linux/delay.h>
   5 #include <linux/cpufreq.h>
   6 #include <linux/jiffies.h>
   7 #include <linux/init.h>
   8 #include <linux/dmi.h>
   9 #include <linux/percpu.h>
  10
  11 #include <asm/delay.h>
  12 #include <asm/tsc.h>
  13 #include <asm/io.h>
  14 #include <asm/timer.h>
  15
  16 #include "mach_timer.h"
  17
  18 static int tsc_disabled;
  19
  20 /*
  21  * On some systems the TSC frequency does not
  22  * change with the cpu frequency. So we need
  23  * an extra value to store the TSC freq
  24  */
  25 unsigned int tsc_khz;
  26 EXPORT_SYMBOL_GPL(tsc_khz);
  27
  28 #ifdef CONFIG_X86_TSC
  29 static int __init tsc_setup(char *str)
  30 {
  31         printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
  32                "cannot disable TSC completely.\n");
  33         tsc_disabled = 1;
  34         return 1;
  35 }
  36 #else
  37 /*
  38  * disable flag for tsc. Takes effect by clearing the TSC cpu flag
  39  * in cpu/common.c
  40  */
  41 static int __init tsc_setup(char *str)
  42 {
  43         setup_clear_cpu_cap(X86_FEATURE_TSC);
  44         return 1;
  45 }
  46 #endif
  47
  48 __setup("notsc", tsc_setup);
  49
  50 /*
  51  * code to mark and check if the TSC is unstable
  52  * due to cpufreq or due to unsynced TSCs
  53  */
  54 static int tsc_unstable;
  55
  56 int check_tsc_unstable(void)
  57 {
  58         return tsc_unstable;
  59 }
  60 EXPORT_SYMBOL_GPL(check_tsc_unstable);
  61
  62 /* Accelerators for sched_clock()
  63  * convert from cycles(64bits) => nanoseconds (64bits)
  64  *  basic equation:
  65  *              ns = cycles / (freq / ns_per_sec)
  66  *              ns = cycles * (ns_per_sec / freq)
  67  *              ns = cycles * (10^9 / (cpu_khz * 10^3))
  68  *              ns = cycles * (10^6 / cpu_khz)
  69  *
  70  *      Then we use scaling math (suggested by george@mvista.com) to get:
  71  *              ns = cycles * (10^6 * SC / cpu_khz) / SC
  72  *              ns = cycles * cyc2ns_scale / SC
  73  *
  74  *      And since SC is a constant power of two, we can convert the div
  75  *  into a shift.
  76  *
  77  *  We can use khz divisor instead of mhz to keep a better precision, since
  78  *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
  79  *  (mathieu.desnoyers@polymtl.ca)
  80  *
  81  *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
  82  */
  83
  84 DEFINE_PER_CPU(unsigned long, cyc2ns);
  85
  86 static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
  87 {
  88         unsigned long long tsc_now, ns_now;
  89         unsigned long flags, *scale;
  90
  91         local_irq_save(flags);
  92         sched_clock_idle_sleep_event();
  93
  94         scale = &per_cpu(cyc2ns, cpu);
  95
  96         rdtscll(tsc_now);
  97         ns_now = __cycles_2_ns(tsc_now);
  98
  99         if (cpu_khz)
 100                 *scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
 101
 102         /*
 103          * Start smoothly with the new frequency:
 104          */
 105         sched_clock_idle_wakeup_event(0);
 106         local_irq_restore(flags);
 107 }
 108
 109 /*
 110  * Scheduler clock - returns current time in nanosec units.
 111  */
 112 unsigned long long native_sched_clock(void)
 113 {
 114         unsigned long long this_offset;
 115
 116         /*
 117          * Fall back to jiffies if there's no TSC available:
 118          * ( But note that we still use it if the TSC is marked
 119          *   unstable. We do this because unlike Time Of Day,
 120          *   the scheduler clock tolerates small errors and it's
 121          *   very important for it to be as fast as the platform
 122          *   can achive it. )
 123          */
 124         if (unlikely(tsc_disabled))
 125                 /* No locking but a rare wrong value is not a big deal: */
 126                 return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
 127
 128         /* read the Time Stamp Counter: */
 129         rdtscll(this_offset);
 130
 131         /* return the value in ns */
 132         return cycles_2_ns(this_offset);
 133 }
 134
 135 /* We need to define a real function for sched_clock, to override the
 136    weak default version */
 137 #ifdef CONFIG_PARAVIRT
 138 unsigned long long sched_clock(void)
 139 {
 140         return paravirt_sched_clock();
 141 }
 142 #else
 143 unsigned long long sched_clock(void)
 144         __attribute__((alias("native_sched_clock")));
 145 #endif
 146
 147 unsigned long native_calculate_cpu_khz(void)
 148 {
 149         unsigned long long start, end;
 150         unsigned long count;
 151         u64 delta64 = (u64)ULLONG_MAX;
 152         int i;
 153         unsigned long flags;
 154
 155         local_irq_save(flags);
 156
 157         /* run 3 times to ensure the cache is warm and to get an accurate reading */
 158         for (i = 0; i < 3; i++) {
 159                 mach_prepare_counter();
 160                 rdtscll(start);
 161                 mach_countup(&count);
 162                 rdtscll(end);
 163
 164                 /*
 165                  * Error: ECTCNEVERSET
 166                  * The CTC wasn't reliable: we got a hit on the very first read,
 167                  * or the CPU was so fast/slow that the quotient wouldn't fit in
 168                  * 32 bits..
 169                  */
 170                 if (count <= 1)
 171                         continue;
 172
 173                 /* cpu freq too slow: */
 174                 if ((end - start) <= CALIBRATE_TIME_MSEC)
 175                         continue;
 176
 177                 /*
 178                  * We want the minimum time of all runs in case one of them
 179                  * is inaccurate due to SMI or other delay
 180                  */
 181                 delta64 = min(delta64, (end - start));
 182         }
 183
 184         /* cpu freq too fast (or every run was bad): */
 185         if (delta64 > (1ULL<<32))
 186                 goto err;
 187
 188         delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
 189         do_div(delta64,CALIBRATE_TIME_MSEC);
 190
 191         local_irq_restore(flags);
 192         return (unsigned long)delta64;
 193 err:
 194         local_irq_restore(flags);
 195         return 0;
 196 }
 197
 198 int recalibrate_cpu_khz(void)
 199 {
 200 #ifndef CONFIG_SMP
 201         unsigned long cpu_khz_old = cpu_khz;
 202
 203         if (cpu_has_tsc) {
 204                 cpu_khz = calculate_cpu_khz();
 205                 tsc_khz = cpu_khz;
 206                 cpu_data(0).loops_per_jiffy =
 207                         cpufreq_scale(cpu_data(0).loops_per_jiffy,
 208                                         cpu_khz_old, cpu_khz);
 209                 return 0;
 210         } else
 211                 return -ENODEV;
 212 #else
 213         return -ENODEV;
 214 #endif
 215 }
 216
 217 EXPORT_SYMBOL(recalibrate_cpu_khz);
 218
 219 #ifdef CONFIG_CPU_FREQ
 220
 221 /*
 222  * if the CPU frequency is scaled, TSC-based delays will need a different
 223  * loops_per_jiffy value to function properly.
 224  */
 225 static unsigned int ref_freq;
 226 static unsigned long loops_per_jiffy_ref;
 227 static unsigned long cpu_khz_ref;
 228
 229 static int
 230 time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
 231 {
 232         struct cpufreq_freqs *freq = data;
 233
 234         if (!ref_freq) {
 235                 if (!freq->old){
 236                         ref_freq = freq->new;
 237                         return 0;
 238                 }
 239                 ref_freq = freq->old;
 240                 loops_per_jiffy_ref = cpu_data(freq->cpu).loops_per_jiffy;
 241                 cpu_khz_ref = cpu_khz;
 242         }
 243
 244         if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
 245             (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
 246             (val == CPUFREQ_RESUMECHANGE)) {
 247                 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
 248                         cpu_data(freq->cpu).loops_per_jiffy =
 249                                 cpufreq_scale(loops_per_jiffy_ref,
 250                                                 ref_freq, freq->new);
 251
 252                 if (cpu_khz) {
 253
 254                         if (num_online_cpus() == 1)
 255                                 cpu_khz = cpufreq_scale(cpu_khz_ref,
 256                                                 ref_freq, freq->new);
 257                         if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
 258                                 tsc_khz = cpu_khz;
 259                                 set_cyc2ns_scale(cpu_khz, freq->cpu);
 260                                 /*
 261                                  * TSC based sched_clock turns
 262                                  * to junk w/ cpufreq
 263                                  */
 264                                 mark_tsc_unstable("cpufreq changes");
 265                         }
 266                 }
 267         }
 268
 269         return 0;
 270 }
 271
 272 static struct notifier_block time_cpufreq_notifier_block = {
 273         .notifier_call  = time_cpufreq_notifier
 274 };
 275
 276 static int __init cpufreq_tsc(void)
 277 {
 278         return cpufreq_register_notifier(&time_cpufreq_notifier_block,
 279                                          CPUFREQ_TRANSITION_NOTIFIER);
 280 }
 281 core_initcall(cpufreq_tsc);
 282
 283 #endif
 284
 285 /* clock source code */
 286
 287 static unsigned long current_tsc_khz;
 288 static struct clocksource clocksource_tsc;
 289
 290 /*
 291  * We compare the TSC to the cycle_last value in the clocksource
 292  * structure to avoid a nasty time-warp issue. This can be observed in
 293  * a very small window right after one CPU updated cycle_last under
 294  * xtime lock and the other CPU reads a TSC value which is smaller
 295  * than the cycle_last reference value due to a TSC which is slighty
 296  * behind. This delta is nowhere else observable, but in that case it
 297  * results in a forward time jump in the range of hours due to the
 298  * unsigned delta calculation of the time keeping core code, which is
 299  * necessary to support wrapping clocksources like pm timer.
 300  */
 301 static cycle_t read_tsc(void)
 302 {
 303         cycle_t ret;
 304
 305         rdtscll(ret);
 306
 307         return ret >= clocksource_tsc.cycle_last ?
 308                 ret : clocksource_tsc.cycle_last;
 309 }
 310
 311 static struct clocksource clocksource_tsc = {
 312         .name                   = "tsc",
 313         .rating                 = 300,
 314         .read                   = read_tsc,
 315         .mask                   = CLOCKSOURCE_MASK(64),
 316         .mult                   = 0, /* to be set */
 317         .shift                  = 22,
 318         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
 319                                   CLOCK_SOURCE_MUST_VERIFY,
 320 };
 321
 322 void mark_tsc_unstable(char *reason)
 323 {
 324         if (!tsc_unstable) {
 325                 tsc_unstable = 1;
 326                 printk("Marking TSC unstable due to: %s.\n", reason);
 327                 /* Can be called before registration */
 328                 if (clocksource_tsc.mult)
 329                         clocksource_change_rating(&clocksource_tsc, 0);
 330                 else
 331                         clocksource_tsc.rating = 0;
 332         }
 333 }
 334 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
 335
 336 static int __init dmi_mark_tsc_unstable(const struct dmi_system_id *d)
 337 {
 338         printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
 339                d->ident);
 340         tsc_unstable = 1;
 341         return 0;
 342 }
 343
 344 /* List of systems that have known TSC problems */
 345 static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
 346         {
 347          .callback = dmi_mark_tsc_unstable,
 348          .ident = "IBM Thinkpad 380XD",
 349          .matches = {
 350                      DMI_MATCH(DMI_BOARD_VENDOR, "IBM"),
 351                      DMI_MATCH(DMI_BOARD_NAME, "2635FA0"),
 352                      },
 353          },
 354          {}
 355 };
 356
 357 /*
 358  * Make an educated guess if the TSC is trustworthy and synchronized
 359  * over all CPUs.
 360  */
 361 __cpuinit int unsynchronized_tsc(void)
 362 {
 363         if (!cpu_has_tsc || tsc_unstable)
 364                 return 1;
 365
 366         /* Anything with constant TSC should be synchronized */
 367         if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
 368                 return 0;
 369
 370         /*
 371          * Intel systems are normally all synchronized.
 372          * Exceptions must mark TSC as unstable:
 373          */
 374         if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
 375                 /* assume multi socket systems are not synchronized: */
 376                 if (num_possible_cpus() > 1)
 377                         tsc_unstable = 1;
 378         }
 379         return tsc_unstable;
 380 }
 381
 382 /*
 383  * Geode_LX - the OLPC CPU has a possibly a very reliable TSC
 384  */
 385 #ifdef CONFIG_MGEODE_LX
 386 /* RTSC counts during suspend */
 387 #define RTSC_SUSP 0x100
 388
 389 static void __init check_geode_tsc_reliable(void)
 390 {
 391         unsigned long res_low, res_high;
 392
 393         rdmsr_safe(MSR_GEODE_BUSCONT_CONF0, &res_low, &res_high);
 394         if (res_low & RTSC_SUSP)
 395                 clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
 396 }
 397 #else
 398 static inline void check_geode_tsc_reliable(void) { }
 399 #endif
 400
 401
 402 void __init tsc_init(void)
 403 {
 404         int cpu;
 405         u64 lpj;
 406
 407         if (!cpu_has_tsc || tsc_disabled) {
 408                 /* Disable the TSC in case of !cpu_has_tsc */
 409                 tsc_disabled = 1;
 410                 return;
 411         }
 412
 413         cpu_khz = calculate_cpu_khz();
 414         tsc_khz = cpu_khz;
 415
 416         if (!cpu_khz) {
 417                 mark_tsc_unstable("could not calculate TSC khz");
 418                 /*
 419                  * We need to disable the TSC completely in this case
 420                  * to prevent sched_clock() from using it.
 421                  */
 422                 tsc_disabled = 1;
 423                 return;
 424         }
 425
 426         lpj = ((u64)tsc_khz * 1000);
 427         do_div(lpj, HZ);
 428         lpj_tsc = lpj;
 429
 430         printk("Detected %lu.%03lu MHz processor.\n",
 431                                 (unsigned long)cpu_khz / 1000,
 432                                 (unsigned long)cpu_khz % 1000);
 433
 434         /*
 435          * Secondary CPUs do not run through tsc_init(), so set up
 436          * all the scale factors for all CPUs, assuming the same
 437          * speed as the bootup CPU. (cpufreq notifiers will fix this
 438          * up if their speed diverges)
 439          */
 440         for_each_possible_cpu(cpu)
 441                 set_cyc2ns_scale(cpu_khz, cpu);
 442
 443         use_tsc_delay();
 444
 445         /* Check and install the TSC clocksource */
 446         dmi_check_system(bad_tsc_dmi_table);
 447
 448         unsynchronized_tsc();
 449         check_geode_tsc_reliable();
 450         current_tsc_khz = tsc_khz;
 451         clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
 452                                                         clocksource_tsc.shift);
 453         /* lower the rating if we already know its unstable: */
 454         if (check_tsc_unstable()) {
 455                 clocksource_tsc.rating = 0;
 456                 clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
 457         }
 458         clocksource_register(&clocksource_tsc);
 459 }