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