1 #include <linux/kernel.h> 2 #include <linux/sched.h> 3 #include <linux/init.h> 4 #include <linux/module.h> 5 #include <linux/timer.h> 6 #include <linux/acpi_pmtmr.h> 7 #include <linux/cpufreq.h> 8 #include <linux/dmi.h> 9 #include <linux/delay.h> 10 #include <linux/clocksource.h> 11 #include <linux/percpu.h> 12 #include <linux/timex.h> 13 14 #include <asm/hpet.h> 15 #include <asm/timer.h> 16 #include <asm/vgtod.h> 17 #include <asm/time.h> 18 #include <asm/delay.h> 19 #include <asm/hypervisor.h> 20 #include <asm/nmi.h> 21 #include <asm/x86_init.h> 22 23 unsigned int __read_mostly cpu_khz; /* TSC clocks / usec, not used here */ 24 EXPORT_SYMBOL(cpu_khz); 25 26 unsigned int __read_mostly tsc_khz; 27 EXPORT_SYMBOL(tsc_khz); 28 29 /* 30 * TSC can be unstable due to cpufreq or due to unsynced TSCs 31 */ 32 static int __read_mostly tsc_unstable; 33 34 /* native_sched_clock() is called before tsc_init(), so 35 we must start with the TSC soft disabled to prevent 36 erroneous rdtsc usage on !cpu_has_tsc processors */ 37 static int __read_mostly tsc_disabled = -1; 38 39 static int tsc_clocksource_reliable; 40 /* 41 * Scheduler clock - returns current time in nanosec units. 42 */ 43 u64 native_sched_clock(void) 44 { 45 u64 this_offset; 46 47 /* 48 * Fall back to jiffies if there's no TSC available: 49 * ( But note that we still use it if the TSC is marked 50 * unstable. We do this because unlike Time Of Day, 51 * the scheduler clock tolerates small errors and it's 52 * very important for it to be as fast as the platform 53 * can achive it. ) 54 */ 55 if (unlikely(tsc_disabled)) { 56 /* No locking but a rare wrong value is not a big deal: */ 57 return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ); 58 } 59 60 /* read the Time Stamp Counter: */ 61 rdtscll(this_offset); 62 63 /* return the value in ns */ 64 return __cycles_2_ns(this_offset); 65 } 66 67 /* We need to define a real function for sched_clock, to override the 68 weak default version */ 69 #ifdef CONFIG_PARAVIRT 70 unsigned long long sched_clock(void) 71 { 72 return paravirt_sched_clock(); 73 } 74 #else 75 unsigned long long 76 sched_clock(void) __attribute__((alias("native_sched_clock"))); 77 #endif 78 79 int check_tsc_unstable(void) 80 { 81 return tsc_unstable; 82 } 83 EXPORT_SYMBOL_GPL(check_tsc_unstable); 84 85 #ifdef CONFIG_X86_TSC 86 int __init notsc_setup(char *str) 87 { 88 printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, " 89 "cannot disable TSC completely.\n"); 90 tsc_disabled = 1; 91 return 1; 92 } 93 #else 94 /* 95 * disable flag for tsc. Takes effect by clearing the TSC cpu flag 96 * in cpu/common.c 97 */ 98 int __init notsc_setup(char *str) 99 { 100 setup_clear_cpu_cap(X86_FEATURE_TSC); 101 return 1; 102 } 103 #endif 104 105 __setup("notsc", notsc_setup); 106 107 static int __init tsc_setup(char *str) 108 { 109 if (!strcmp(str, "reliable")) 110 tsc_clocksource_reliable = 1; 111 return 1; 112 } 113 114 __setup("tsc=", tsc_setup); 115 116 #define MAX_RETRIES 5 117 #define SMI_TRESHOLD 50000 118 119 /* 120 * Read TSC and the reference counters. Take care of SMI disturbance 121 */ 122 static u64 tsc_read_refs(u64 *p, int hpet) 123 { 124 u64 t1, t2; 125 int i; 126 127 for (i = 0; i < MAX_RETRIES; i++) { 128 t1 = get_cycles(); 129 if (hpet) 130 *p = hpet_readl(HPET_COUNTER) & 0xFFFFFFFF; 131 else 132 *p = acpi_pm_read_early(); 133 t2 = get_cycles(); 134 if ((t2 - t1) < SMI_TRESHOLD) 135 return t2; 136 } 137 return ULLONG_MAX; 138 } 139 140 /* 141 * Calculate the TSC frequency from HPET reference 142 */ 143 static unsigned long calc_hpet_ref(u64 deltatsc, u64 hpet1, u64 hpet2) 144 { 145 u64 tmp; 146 147 if (hpet2 < hpet1) 148 hpet2 += 0x100000000ULL; 149 hpet2 -= hpet1; 150 tmp = ((u64)hpet2 * hpet_readl(HPET_PERIOD)); 151 do_div(tmp, 1000000); 152 do_div(deltatsc, tmp); 153 154 return (unsigned long) deltatsc; 155 } 156 157 /* 158 * Calculate the TSC frequency from PMTimer reference 159 */ 160 static unsigned long calc_pmtimer_ref(u64 deltatsc, u64 pm1, u64 pm2) 161 { 162 u64 tmp; 163 164 if (!pm1 && !pm2) 165 return ULONG_MAX; 166 167 if (pm2 < pm1) 168 pm2 += (u64)ACPI_PM_OVRRUN; 169 pm2 -= pm1; 170 tmp = pm2 * 1000000000LL; 171 do_div(tmp, PMTMR_TICKS_PER_SEC); 172 do_div(deltatsc, tmp); 173 174 return (unsigned long) deltatsc; 175 } 176 177 #define CAL_MS 10 178 #define CAL_LATCH (CLOCK_TICK_RATE / (1000 / CAL_MS)) 179 #define CAL_PIT_LOOPS 1000 180 181 #define CAL2_MS 50 182 #define CAL2_LATCH (CLOCK_TICK_RATE / (1000 / CAL2_MS)) 183 #define CAL2_PIT_LOOPS 5000 184 185 186 /* 187 * Try to calibrate the TSC against the Programmable 188 * Interrupt Timer and return the frequency of the TSC 189 * in kHz. 190 * 191 * Return ULONG_MAX on failure to calibrate. 192 */ 193 static unsigned long pit_calibrate_tsc(u32 latch, unsigned long ms, int loopmin) 194 { 195 u64 tsc, t1, t2, delta; 196 unsigned long tscmin, tscmax; 197 int pitcnt; 198 199 /* Set the Gate high, disable speaker */ 200 outb((inb(0x61) & ~0x02) | 0x01, 0x61); 201 202 /* 203 * Setup CTC channel 2* for mode 0, (interrupt on terminal 204 * count mode), binary count. Set the latch register to 50ms 205 * (LSB then MSB) to begin countdown. 206 */ 207 outb(0xb0, 0x43); 208 outb(latch & 0xff, 0x42); 209 outb(latch >> 8, 0x42); 210 211 tsc = t1 = t2 = get_cycles(); 212 213 pitcnt = 0; 214 tscmax = 0; 215 tscmin = ULONG_MAX; 216 while ((inb(0x61) & 0x20) == 0) { 217 t2 = get_cycles(); 218 delta = t2 - tsc; 219 tsc = t2; 220 if ((unsigned long) delta < tscmin) 221 tscmin = (unsigned int) delta; 222 if ((unsigned long) delta > tscmax) 223 tscmax = (unsigned int) delta; 224 pitcnt++; 225 } 226 227 /* 228 * Sanity checks: 229 * 230 * If we were not able to read the PIT more than loopmin 231 * times, then we have been hit by a massive SMI 232 * 233 * If the maximum is 10 times larger than the minimum, 234 * then we got hit by an SMI as well. 235 */ 236 if (pitcnt < loopmin || tscmax > 10 * tscmin) 237 return ULONG_MAX; 238 239 /* Calculate the PIT value */ 240 delta = t2 - t1; 241 do_div(delta, ms); 242 return delta; 243 } 244 245 /* 246 * This reads the current MSB of the PIT counter, and 247 * checks if we are running on sufficiently fast and 248 * non-virtualized hardware. 249 * 250 * Our expectations are: 251 * 252 * - the PIT is running at roughly 1.19MHz 253 * 254 * - each IO is going to take about 1us on real hardware, 255 * but we allow it to be much faster (by a factor of 10) or 256 * _slightly_ slower (ie we allow up to a 2us read+counter 257 * update - anything else implies a unacceptably slow CPU 258 * or PIT for the fast calibration to work. 259 * 260 * - with 256 PIT ticks to read the value, we have 214us to 261 * see the same MSB (and overhead like doing a single TSC 262 * read per MSB value etc). 263 * 264 * - We're doing 2 reads per loop (LSB, MSB), and we expect 265 * them each to take about a microsecond on real hardware. 266 * So we expect a count value of around 100. But we'll be 267 * generous, and accept anything over 50. 268 * 269 * - if the PIT is stuck, and we see *many* more reads, we 270 * return early (and the next caller of pit_expect_msb() 271 * then consider it a failure when they don't see the 272 * next expected value). 273 * 274 * These expectations mean that we know that we have seen the 275 * transition from one expected value to another with a fairly 276 * high accuracy, and we didn't miss any events. We can thus 277 * use the TSC value at the transitions to calculate a pretty 278 * good value for the TSC frequencty. 279 */ 280 static inline int pit_verify_msb(unsigned char val) 281 { 282 /* Ignore LSB */ 283 inb(0x42); 284 return inb(0x42) == val; 285 } 286 287 static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *deltap) 288 { 289 int count; 290 u64 tsc = 0; 291 292 for (count = 0; count < 50000; count++) { 293 if (!pit_verify_msb(val)) 294 break; 295 tsc = get_cycles(); 296 } 297 *deltap = get_cycles() - tsc; 298 *tscp = tsc; 299 300 /* 301 * We require _some_ success, but the quality control 302 * will be based on the error terms on the TSC values. 303 */ 304 return count > 5; 305 } 306 307 /* 308 * How many MSB values do we want to see? We aim for 309 * a maximum error rate of 500ppm (in practice the 310 * real error is much smaller), but refuse to spend 311 * more than 25ms on it. 312 */ 313 #define MAX_QUICK_PIT_MS 25 314 #define MAX_QUICK_PIT_ITERATIONS (MAX_QUICK_PIT_MS * PIT_TICK_RATE / 1000 / 256) 315 316 static unsigned long quick_pit_calibrate(void) 317 { 318 int i; 319 u64 tsc, delta; 320 unsigned long d1, d2; 321 322 /* Set the Gate high, disable speaker */ 323 outb((inb(0x61) & ~0x02) | 0x01, 0x61); 324 325 /* 326 * Counter 2, mode 0 (one-shot), binary count 327 * 328 * NOTE! Mode 2 decrements by two (and then the 329 * output is flipped each time, giving the same 330 * final output frequency as a decrement-by-one), 331 * so mode 0 is much better when looking at the 332 * individual counts. 333 */ 334 outb(0xb0, 0x43); 335 336 /* Start at 0xffff */ 337 outb(0xff, 0x42); 338 outb(0xff, 0x42); 339 340 /* 341 * The PIT starts counting at the next edge, so we 342 * need to delay for a microsecond. The easiest way 343 * to do that is to just read back the 16-bit counter 344 * once from the PIT. 345 */ 346 pit_verify_msb(0); 347 348 if (pit_expect_msb(0xff, &tsc, &d1)) { 349 for (i = 1; i <= MAX_QUICK_PIT_ITERATIONS; i++) { 350 if (!pit_expect_msb(0xff-i, &delta, &d2)) 351 break; 352 353 /* 354 * Iterate until the error is less than 500 ppm 355 */ 356 delta -= tsc; 357 if (d1+d2 >= delta >> 11) 358 continue; 359 360 /* 361 * Check the PIT one more time to verify that 362 * all TSC reads were stable wrt the PIT. 363 * 364 * This also guarantees serialization of the 365 * last cycle read ('d2') in pit_expect_msb. 366 */ 367 if (!pit_verify_msb(0xfe - i)) 368 break; 369 goto success; 370 } 371 } 372 printk("Fast TSC calibration failed\n"); 373 return 0; 374 375 success: 376 /* 377 * Ok, if we get here, then we've seen the 378 * MSB of the PIT decrement 'i' times, and the 379 * error has shrunk to less than 500 ppm. 380 * 381 * As a result, we can depend on there not being 382 * any odd delays anywhere, and the TSC reads are 383 * reliable (within the error). We also adjust the 384 * delta to the middle of the error bars, just 385 * because it looks nicer. 386 * 387 * kHz = ticks / time-in-seconds / 1000; 388 * kHz = (t2 - t1) / (I * 256 / PIT_TICK_RATE) / 1000 389 * kHz = ((t2 - t1) * PIT_TICK_RATE) / (I * 256 * 1000) 390 */ 391 delta += (long)(d2 - d1)/2; 392 delta *= PIT_TICK_RATE; 393 do_div(delta, i*256*1000); 394 printk("Fast TSC calibration using PIT\n"); 395 return delta; 396 } 397 398 /** 399 * native_calibrate_tsc - calibrate the tsc on boot 400 */ 401 unsigned long native_calibrate_tsc(void) 402 { 403 u64 tsc1, tsc2, delta, ref1, ref2; 404 unsigned long tsc_pit_min = ULONG_MAX, tsc_ref_min = ULONG_MAX; 405 unsigned long flags, latch, ms, fast_calibrate; 406 int hpet = is_hpet_enabled(), i, loopmin; 407 408 local_irq_save(flags); 409 fast_calibrate = quick_pit_calibrate(); 410 local_irq_restore(flags); 411 if (fast_calibrate) 412 return fast_calibrate; 413 414 /* 415 * Run 5 calibration loops to get the lowest frequency value 416 * (the best estimate). We use two different calibration modes 417 * here: 418 * 419 * 1) PIT loop. We set the PIT Channel 2 to oneshot mode and 420 * load a timeout of 50ms. We read the time right after we 421 * started the timer and wait until the PIT count down reaches 422 * zero. In each wait loop iteration we read the TSC and check 423 * the delta to the previous read. We keep track of the min 424 * and max values of that delta. The delta is mostly defined 425 * by the IO time of the PIT access, so we can detect when a 426 * SMI/SMM disturbance happend between the two reads. If the 427 * maximum time is significantly larger than the minimum time, 428 * then we discard the result and have another try. 429 * 430 * 2) Reference counter. If available we use the HPET or the 431 * PMTIMER as a reference to check the sanity of that value. 432 * We use separate TSC readouts and check inside of the 433 * reference read for a SMI/SMM disturbance. We dicard 434 * disturbed values here as well. We do that around the PIT 435 * calibration delay loop as we have to wait for a certain 436 * amount of time anyway. 437 */ 438 439 /* Preset PIT loop values */ 440 latch = CAL_LATCH; 441 ms = CAL_MS; 442 loopmin = CAL_PIT_LOOPS; 443 444 for (i = 0; i < 3; i++) { 445 unsigned long tsc_pit_khz; 446 447 /* 448 * Read the start value and the reference count of 449 * hpet/pmtimer when available. Then do the PIT 450 * calibration, which will take at least 50ms, and 451 * read the end value. 452 */ 453 local_irq_save(flags); 454 tsc1 = tsc_read_refs(&ref1, hpet); 455 tsc_pit_khz = pit_calibrate_tsc(latch, ms, loopmin); 456 tsc2 = tsc_read_refs(&ref2, hpet); 457 local_irq_restore(flags); 458 459 /* Pick the lowest PIT TSC calibration so far */ 460 tsc_pit_min = min(tsc_pit_min, tsc_pit_khz); 461 462 /* hpet or pmtimer available ? */ 463 if (!hpet && !ref1 && !ref2) 464 continue; 465 466 /* Check, whether the sampling was disturbed by an SMI */ 467 if (tsc1 == ULLONG_MAX || tsc2 == ULLONG_MAX) 468 continue; 469 470 tsc2 = (tsc2 - tsc1) * 1000000LL; 471 if (hpet) 472 tsc2 = calc_hpet_ref(tsc2, ref1, ref2); 473 else 474 tsc2 = calc_pmtimer_ref(tsc2, ref1, ref2); 475 476 tsc_ref_min = min(tsc_ref_min, (unsigned long) tsc2); 477 478 /* Check the reference deviation */ 479 delta = ((u64) tsc_pit_min) * 100; 480 do_div(delta, tsc_ref_min); 481 482 /* 483 * If both calibration results are inside a 10% window 484 * then we can be sure, that the calibration 485 * succeeded. We break out of the loop right away. We 486 * use the reference value, as it is more precise. 487 */ 488 if (delta >= 90 && delta <= 110) { 489 printk(KERN_INFO 490 "TSC: PIT calibration matches %s. %d loops\n", 491 hpet ? "HPET" : "PMTIMER", i + 1); 492 return tsc_ref_min; 493 } 494 495 /* 496 * Check whether PIT failed more than once. This 497 * happens in virtualized environments. We need to 498 * give the virtual PC a slightly longer timeframe for 499 * the HPET/PMTIMER to make the result precise. 500 */ 501 if (i == 1 && tsc_pit_min == ULONG_MAX) { 502 latch = CAL2_LATCH; 503 ms = CAL2_MS; 504 loopmin = CAL2_PIT_LOOPS; 505 } 506 } 507 508 /* 509 * Now check the results. 510 */ 511 if (tsc_pit_min == ULONG_MAX) { 512 /* PIT gave no useful value */ 513 printk(KERN_WARNING "TSC: Unable to calibrate against PIT\n"); 514 515 /* We don't have an alternative source, disable TSC */ 516 if (!hpet && !ref1 && !ref2) { 517 printk("TSC: No reference (HPET/PMTIMER) available\n"); 518 return 0; 519 } 520 521 /* The alternative source failed as well, disable TSC */ 522 if (tsc_ref_min == ULONG_MAX) { 523 printk(KERN_WARNING "TSC: HPET/PMTIMER calibration " 524 "failed.\n"); 525 return 0; 526 } 527 528 /* Use the alternative source */ 529 printk(KERN_INFO "TSC: using %s reference calibration\n", 530 hpet ? "HPET" : "PMTIMER"); 531 532 return tsc_ref_min; 533 } 534 535 /* We don't have an alternative source, use the PIT calibration value */ 536 if (!hpet && !ref1 && !ref2) { 537 printk(KERN_INFO "TSC: Using PIT calibration value\n"); 538 return tsc_pit_min; 539 } 540 541 /* The alternative source failed, use the PIT calibration value */ 542 if (tsc_ref_min == ULONG_MAX) { 543 printk(KERN_WARNING "TSC: HPET/PMTIMER calibration failed. " 544 "Using PIT calibration\n"); 545 return tsc_pit_min; 546 } 547 548 /* 549 * The calibration values differ too much. In doubt, we use 550 * the PIT value as we know that there are PMTIMERs around 551 * running at double speed. At least we let the user know: 552 */ 553 printk(KERN_WARNING "TSC: PIT calibration deviates from %s: %lu %lu.\n", 554 hpet ? "HPET" : "PMTIMER", tsc_pit_min, tsc_ref_min); 555 printk(KERN_INFO "TSC: Using PIT calibration value\n"); 556 return tsc_pit_min; 557 } 558 559 int recalibrate_cpu_khz(void) 560 { 561 #ifndef CONFIG_SMP 562 unsigned long cpu_khz_old = cpu_khz; 563 564 if (cpu_has_tsc) { 565 tsc_khz = x86_platform.calibrate_tsc(); 566 cpu_khz = tsc_khz; 567 cpu_data(0).loops_per_jiffy = 568 cpufreq_scale(cpu_data(0).loops_per_jiffy, 569 cpu_khz_old, cpu_khz); 570 return 0; 571 } else 572 return -ENODEV; 573 #else 574 return -ENODEV; 575 #endif 576 } 577 578 EXPORT_SYMBOL(recalibrate_cpu_khz); 579 580 581 /* Accelerators for sched_clock() 582 * convert from cycles(64bits) => nanoseconds (64bits) 583 * basic equation: 584 * ns = cycles / (freq / ns_per_sec) 585 * ns = cycles * (ns_per_sec / freq) 586 * ns = cycles * (10^9 / (cpu_khz * 10^3)) 587 * ns = cycles * (10^6 / cpu_khz) 588 * 589 * Then we use scaling math (suggested by george@mvista.com) to get: 590 * ns = cycles * (10^6 * SC / cpu_khz) / SC 591 * ns = cycles * cyc2ns_scale / SC 592 * 593 * And since SC is a constant power of two, we can convert the div 594 * into a shift. 595 * 596 * We can use khz divisor instead of mhz to keep a better precision, since 597 * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits. 598 * (mathieu.desnoyers@polymtl.ca) 599 * 600 * -johnstul@us.ibm.com "math is hard, lets go shopping!" 601 */ 602 603 DEFINE_PER_CPU(unsigned long, cyc2ns); 604 DEFINE_PER_CPU(unsigned long long, cyc2ns_offset); 605 606 static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu) 607 { 608 unsigned long long tsc_now, ns_now, *offset; 609 unsigned long flags, *scale; 610 611 local_irq_save(flags); 612 sched_clock_idle_sleep_event(); 613 614 scale = &per_cpu(cyc2ns, cpu); 615 offset = &per_cpu(cyc2ns_offset, cpu); 616 617 rdtscll(tsc_now); 618 ns_now = __cycles_2_ns(tsc_now); 619 620 if (cpu_khz) { 621 *scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz; 622 *offset = ns_now - (tsc_now * *scale >> CYC2NS_SCALE_FACTOR); 623 } 624 625 sched_clock_idle_wakeup_event(0); 626 local_irq_restore(flags); 627 } 628 629 #ifdef CONFIG_CPU_FREQ 630 631 /* Frequency scaling support. Adjust the TSC based timer when the cpu frequency 632 * changes. 633 * 634 * RED-PEN: On SMP we assume all CPUs run with the same frequency. It's 635 * not that important because current Opteron setups do not support 636 * scaling on SMP anyroads. 637 * 638 * Should fix up last_tsc too. Currently gettimeofday in the 639 * first tick after the change will be slightly wrong. 640 */ 641 642 static unsigned int ref_freq; 643 static unsigned long loops_per_jiffy_ref; 644 static unsigned long tsc_khz_ref; 645 646 static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, 647 void *data) 648 { 649 struct cpufreq_freqs *freq = data; 650 unsigned long *lpj; 651 652 if (cpu_has(&cpu_data(freq->cpu), X86_FEATURE_CONSTANT_TSC)) 653 return 0; 654 655 lpj = &boot_cpu_data.loops_per_jiffy; 656 #ifdef CONFIG_SMP 657 if (!(freq->flags & CPUFREQ_CONST_LOOPS)) 658 lpj = &cpu_data(freq->cpu).loops_per_jiffy; 659 #endif 660 661 if (!ref_freq) { 662 ref_freq = freq->old; 663 loops_per_jiffy_ref = *lpj; 664 tsc_khz_ref = tsc_khz; 665 } 666 if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) || 667 (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) || 668 (val == CPUFREQ_RESUMECHANGE)) { 669 *lpj = cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new); 670 671 tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new); 672 if (!(freq->flags & CPUFREQ_CONST_LOOPS)) 673 mark_tsc_unstable("cpufreq changes"); 674 } 675 676 set_cyc2ns_scale(tsc_khz, freq->cpu); 677 678 return 0; 679 } 680 681 static struct notifier_block time_cpufreq_notifier_block = { 682 .notifier_call = time_cpufreq_notifier 683 }; 684 685 static int __init cpufreq_tsc(void) 686 { 687 if (!cpu_has_tsc) 688 return 0; 689 if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) 690 return 0; 691 cpufreq_register_notifier(&time_cpufreq_notifier_block, 692 CPUFREQ_TRANSITION_NOTIFIER); 693 return 0; 694 } 695 696 core_initcall(cpufreq_tsc); 697 698 #endif /* CONFIG_CPU_FREQ */ 699 700 /* clocksource code */ 701 702 static struct clocksource clocksource_tsc; 703 704 /* 705 * We compare the TSC to the cycle_last value in the clocksource 706 * structure to avoid a nasty time-warp. This can be observed in a 707 * very small window right after one CPU updated cycle_last under 708 * xtime/vsyscall_gtod lock and the other CPU reads a TSC value which 709 * is smaller than the cycle_last reference value due to a TSC which 710 * is slighty behind. This delta is nowhere else observable, but in 711 * that case it results in a forward time jump in the range of hours 712 * due to the unsigned delta calculation of the time keeping core 713 * code, which is necessary to support wrapping clocksources like pm 714 * timer. 715 */ 716 static cycle_t read_tsc(struct clocksource *cs) 717 { 718 cycle_t ret = (cycle_t)get_cycles(); 719 720 return ret >= clocksource_tsc.cycle_last ? 721 ret : clocksource_tsc.cycle_last; 722 } 723 724 #ifdef CONFIG_X86_64 725 static cycle_t __vsyscall_fn vread_tsc(void) 726 { 727 cycle_t ret; 728 729 /* 730 * Surround the RDTSC by barriers, to make sure it's not 731 * speculated to outside the seqlock critical section and 732 * does not cause time warps: 733 */ 734 rdtsc_barrier(); 735 ret = (cycle_t)vget_cycles(); 736 rdtsc_barrier(); 737 738 return ret >= __vsyscall_gtod_data.clock.cycle_last ? 739 ret : __vsyscall_gtod_data.clock.cycle_last; 740 } 741 #endif 742 743 static void resume_tsc(void) 744 { 745 clocksource_tsc.cycle_last = 0; 746 } 747 748 static struct clocksource clocksource_tsc = { 749 .name = "tsc", 750 .rating = 300, 751 .read = read_tsc, 752 .resume = resume_tsc, 753 .mask = CLOCKSOURCE_MASK(64), 754 .shift = 22, 755 .flags = CLOCK_SOURCE_IS_CONTINUOUS | 756 CLOCK_SOURCE_MUST_VERIFY, 757 #ifdef CONFIG_X86_64 758 .vread = vread_tsc, 759 #endif 760 }; 761 762 void mark_tsc_unstable(char *reason) 763 { 764 if (!tsc_unstable) { 765 tsc_unstable = 1; 766 sched_clock_stable = 0; 767 printk(KERN_INFO "Marking TSC unstable due to %s\n", reason); 768 /* Change only the rating, when not registered */ 769 if (clocksource_tsc.mult) 770 clocksource_mark_unstable(&clocksource_tsc); 771 else { 772 clocksource_tsc.flags |= CLOCK_SOURCE_UNSTABLE; 773 clocksource_tsc.rating = 0; 774 } 775 } 776 } 777 778 EXPORT_SYMBOL_GPL(mark_tsc_unstable); 779 780 static int __init dmi_mark_tsc_unstable(const struct dmi_system_id *d) 781 { 782 printk(KERN_NOTICE "%s detected: marking TSC unstable.\n", 783 d->ident); 784 tsc_unstable = 1; 785 return 0; 786 } 787 788 /* List of systems that have known TSC problems */ 789 static struct dmi_system_id __initdata bad_tsc_dmi_table[] = { 790 { 791 .callback = dmi_mark_tsc_unstable, 792 .ident = "IBM Thinkpad 380XD", 793 .matches = { 794 DMI_MATCH(DMI_BOARD_VENDOR, "IBM"), 795 DMI_MATCH(DMI_BOARD_NAME, "2635FA0"), 796 }, 797 }, 798 {} 799 }; 800 801 static void __init check_system_tsc_reliable(void) 802 { 803 #ifdef CONFIG_MGEODE_LX 804 /* RTSC counts during suspend */ 805 #define RTSC_SUSP 0x100 806 unsigned long res_low, res_high; 807 808 rdmsr_safe(MSR_GEODE_BUSCONT_CONF0, &res_low, &res_high); 809 /* Geode_LX - the OLPC CPU has a possibly a very reliable TSC */ 810 if (res_low & RTSC_SUSP) 811 tsc_clocksource_reliable = 1; 812 #endif 813 if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) 814 tsc_clocksource_reliable = 1; 815 } 816 817 /* 818 * Make an educated guess if the TSC is trustworthy and synchronized 819 * over all CPUs. 820 */ 821 __cpuinit int unsynchronized_tsc(void) 822 { 823 if (!cpu_has_tsc || tsc_unstable) 824 return 1; 825 826 #ifdef CONFIG_SMP 827 if (apic_is_clustered_box()) 828 return 1; 829 #endif 830 831 if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) 832 return 0; 833 /* 834 * Intel systems are normally all synchronized. 835 * Exceptions must mark TSC as unstable: 836 */ 837 if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) { 838 /* assume multi socket systems are not synchronized: */ 839 if (num_possible_cpus() > 1) 840 tsc_unstable = 1; 841 } 842 843 return tsc_unstable; 844 } 845 846 static void __init init_tsc_clocksource(void) 847 { 848 clocksource_tsc.mult = clocksource_khz2mult(tsc_khz, 849 clocksource_tsc.shift); 850 if (tsc_clocksource_reliable) 851 clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY; 852 /* lower the rating if we already know its unstable: */ 853 if (check_tsc_unstable()) { 854 clocksource_tsc.rating = 0; 855 clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS; 856 } 857 clocksource_register(&clocksource_tsc); 858 } 859 860 #ifdef CONFIG_X86_64 861 /* 862 * calibrate_cpu is used on systems with fixed rate TSCs to determine 863 * processor frequency 864 */ 865 #define TICK_COUNT 100000000 866 static unsigned long __init calibrate_cpu(void) 867 { 868 int tsc_start, tsc_now; 869 int i, no_ctr_free; 870 unsigned long evntsel3 = 0, pmc3 = 0, pmc_now = 0; 871 unsigned long flags; 872 873 for (i = 0; i < 4; i++) 874 if (avail_to_resrv_perfctr_nmi_bit(i)) 875 break; 876 no_ctr_free = (i == 4); 877 if (no_ctr_free) { 878 WARN(1, KERN_WARNING "Warning: AMD perfctrs busy ... " 879 "cpu_khz value may be incorrect.\n"); 880 i = 3; 881 rdmsrl(MSR_K7_EVNTSEL3, evntsel3); 882 wrmsrl(MSR_K7_EVNTSEL3, 0); 883 rdmsrl(MSR_K7_PERFCTR3, pmc3); 884 } else { 885 reserve_perfctr_nmi(MSR_K7_PERFCTR0 + i); 886 reserve_evntsel_nmi(MSR_K7_EVNTSEL0 + i); 887 } 888 local_irq_save(flags); 889 /* start measuring cycles, incrementing from 0 */ 890 wrmsrl(MSR_K7_PERFCTR0 + i, 0); 891 wrmsrl(MSR_K7_EVNTSEL0 + i, 1 << 22 | 3 << 16 | 0x76); 892 rdtscl(tsc_start); 893 do { 894 rdmsrl(MSR_K7_PERFCTR0 + i, pmc_now); 895 tsc_now = get_cycles(); 896 } while ((tsc_now - tsc_start) < TICK_COUNT); 897 898 local_irq_restore(flags); 899 if (no_ctr_free) { 900 wrmsrl(MSR_K7_EVNTSEL3, 0); 901 wrmsrl(MSR_K7_PERFCTR3, pmc3); 902 wrmsrl(MSR_K7_EVNTSEL3, evntsel3); 903 } else { 904 release_perfctr_nmi(MSR_K7_PERFCTR0 + i); 905 release_evntsel_nmi(MSR_K7_EVNTSEL0 + i); 906 } 907 908 return pmc_now * tsc_khz / (tsc_now - tsc_start); 909 } 910 #else 911 static inline unsigned long calibrate_cpu(void) { return cpu_khz; } 912 #endif 913 914 void __init tsc_init(void) 915 { 916 u64 lpj; 917 int cpu; 918 919 x86_init.timers.tsc_pre_init(); 920 921 if (!cpu_has_tsc) 922 return; 923 924 tsc_khz = x86_platform.calibrate_tsc(); 925 cpu_khz = tsc_khz; 926 927 if (!tsc_khz) { 928 mark_tsc_unstable("could not calculate TSC khz"); 929 return; 930 } 931 932 if (cpu_has(&boot_cpu_data, X86_FEATURE_CONSTANT_TSC) && 933 (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)) 934 cpu_khz = calibrate_cpu(); 935 936 printk("Detected %lu.%03lu MHz processor.\n", 937 (unsigned long)cpu_khz / 1000, 938 (unsigned long)cpu_khz % 1000); 939 940 /* 941 * Secondary CPUs do not run through tsc_init(), so set up 942 * all the scale factors for all CPUs, assuming the same 943 * speed as the bootup CPU. (cpufreq notifiers will fix this 944 * up if their speed diverges) 945 */ 946 for_each_possible_cpu(cpu) 947 set_cyc2ns_scale(cpu_khz, cpu); 948 949 if (tsc_disabled > 0) 950 return; 951 952 /* now allow native_sched_clock() to use rdtsc */ 953 tsc_disabled = 0; 954 955 lpj = ((u64)tsc_khz * 1000); 956 do_div(lpj, HZ); 957 lpj_fine = lpj; 958 959 use_tsc_delay(); 960 /* Check and install the TSC clocksource */ 961 dmi_check_system(bad_tsc_dmi_table); 962 963 if (unsynchronized_tsc()) 964 mark_tsc_unstable("TSCs unsynchronized"); 965 966 check_system_tsc_reliable(); 967 init_tsc_clocksource(); 968 } 969 970