include/qemu/timer.h

   1 #ifndef QEMU_TIMER_H
   2 #define QEMU_TIMER_H
   3
   4 #include "qemu/typedefs.h"
   5 #include "qemu-common.h"
   6 #include "qemu/notify.h"
   7
   8 /* timers */
   9
  10 #define SCALE_MS 1000000
  11 #define SCALE_US 1000
  12 #define SCALE_NS 1
  13
  14 /**
  15  * QEMUClockType:
  16  *
  17  * The following clock types are available:
  18  *
  19  * @QEMU_CLOCK_REALTIME: Real time clock
  20  *
  21  * The real time clock should be used only for stuff which does not
  22  * change the virtual machine state, as it is run even if the virtual
  23  * machine is stopped. The real time clock has a frequency of 1000
  24  * Hz.
  25  *
  26  * @QEMU_CLOCK_VIRTUAL: virtual clock
  27  *
  28  * The virtual clock is only run during the emulation. It is stopped
  29  * when the virtual machine is stopped. Virtual timers use a high
  30  * precision clock, usually cpu cycles (use ticks_per_sec).
  31  *
  32  * @QEMU_CLOCK_HOST: host clock
  33  *
  34  * The host clock should be use for device models that emulate accurate
  35  * real time sources. It will continue to run when the virtual machine
  36  * is suspended, and it will reflect system time changes the host may
  37  * undergo (e.g. due to NTP). The host clock has the same precision as
  38  * the virtual clock.
  39  */
  40
  41 typedef enum {
  42     QEMU_CLOCK_REALTIME = 0,
  43     QEMU_CLOCK_VIRTUAL = 1,
  44     QEMU_CLOCK_HOST = 2,
  45     QEMU_CLOCK_MAX
  46 } QEMUClockType;
  47
  48 typedef struct QEMUTimerList QEMUTimerList;
  49
  50 struct QEMUTimerListGroup {
  51     QEMUTimerList *tl[QEMU_CLOCK_MAX];
  52 };
  53
  54 typedef void QEMUTimerCB(void *opaque);
  55 typedef void QEMUTimerListNotifyCB(void *opaque);
  56
  57 struct QEMUTimer {
  58     int64_t expire_time;        /* in nanoseconds */
  59     QEMUTimerList *timer_list;
  60     QEMUTimerCB *cb;
  61     void *opaque;
  62     QEMUTimer *next;
  63     int scale;
  64 };
  65
  66 extern QEMUTimerListGroup main_loop_tlg;
  67
  68 /*
  69  * QEMUClockType
  70  */
  71
  72 /*
  73  * qemu_clock_get_ns;
  74  * @type: the clock type
  75  *
  76  * Get the nanosecond value of a clock with
  77  * type @type
  78  *
  79  * Returns: the clock value in nanoseconds
  80  */
  81 int64_t qemu_clock_get_ns(QEMUClockType type);
  82
  83 /**
  84  * qemu_clock_get_ms;
  85  * @type: the clock type
  86  *
  87  * Get the millisecond value of a clock with
  88  * type @type
  89  *
  90  * Returns: the clock value in milliseconds
  91  */
  92 static inline int64_t qemu_clock_get_ms(QEMUClockType type)
  93 {
  94     return qemu_clock_get_ns(type) / SCALE_MS;
  95 }
  96
  97 /**
  98  * qemu_clock_get_us;
  99  * @type: the clock type
 100  *
 101  * Get the microsecond value of a clock with
 102  * type @type
 103  *
 104  * Returns: the clock value in microseconds
 105  */
 106 static inline int64_t qemu_clock_get_us(QEMUClockType type)
 107 {
 108     return qemu_clock_get_ns(type) / SCALE_US;
 109 }
 110
 111 /**
 112  * qemu_clock_has_timers:
 113  * @type: the clock type
 114  *
 115  * Determines whether a clock's default timer list
 116  * has timers attached
 117  *
 118  * Note that this function should not be used when other threads also access
 119  * the timer list.  The return value may be outdated by the time it is acted
 120  * upon.
 121  *
 122  * Returns: true if the clock's default timer list
 123  * has timers attached
 124  */
 125 bool qemu_clock_has_timers(QEMUClockType type);
 126
 127 /**
 128  * qemu_clock_expired:
 129  * @type: the clock type
 130  *
 131  * Determines whether a clock's default timer list
 132  * has an expired clock.
 133  *
 134  * Returns: true if the clock's default timer list has
 135  * an expired timer
 136  */
 137 bool qemu_clock_expired(QEMUClockType type);
 138
 139 /**
 140  * qemu_clock_use_for_deadline:
 141  * @type: the clock type
 142  *
 143  * Determine whether a clock should be used for deadline
 144  * calculations. Some clocks, for instance vm_clock with
 145  * use_icount set, do not count in nanoseconds. Such clocks
 146  * are not used for deadline calculations, and are presumed
 147  * to interrupt any poll using qemu_notify/aio_notify
 148  * etc.
 149  *
 150  * Returns: true if the clock runs in nanoseconds and
 151  * should be used for a deadline.
 152  */
 153 bool qemu_clock_use_for_deadline(QEMUClockType type);
 154
 155 /**
 156  * qemu_clock_deadline_ns_all:
 157  * @type: the clock type
 158  *
 159  * Calculate the deadline across all timer lists associated
 160  * with a clock (as opposed to just the default one)
 161  * in nanoseconds, or -1 if no timer is set to expire.
 162  *
 163  * Returns: time until expiry in nanoseconds or -1
 164  */
 165 int64_t qemu_clock_deadline_ns_all(QEMUClockType type);
 166
 167 /**
 168  * qemu_clock_get_main_loop_timerlist:
 169  * @type: the clock type
 170  *
 171  * Return the default timer list assocatiated with a clock.
 172  *
 173  * Returns: the default timer list
 174  */
 175 QEMUTimerList *qemu_clock_get_main_loop_timerlist(QEMUClockType type);
 176
 177 /**
 178  * qemu_clock_nofify:
 179  * @type: the clock type
 180  *
 181  * Call the notifier callback connected with the default timer
 182  * list linked to the clock, or qemu_notify() if none.
 183  */
 184 void qemu_clock_notify(QEMUClockType type);
 185
 186 /**
 187  * qemu_clock_enable:
 188  * @type: the clock type
 189  * @enabled: true to enable, false to disable
 190  *
 191  * Enable or disable a clock
 192  * Disabling the clock will wait for related timerlists to stop
 193  * executing qemu_run_timers.  Thus, this functions should not
 194  * be used from the callback of a timer that is based on @clock.
 195  * Doing so would cause a deadlock.
 196  *
 197  * Caller should hold BQL.
 198  */
 199 void qemu_clock_enable(QEMUClockType type, bool enabled);
 200
 201 /**
 202  * qemu_clock_warp:
 203  * @type: the clock type
 204  *
 205  * Warp a clock to a new value
 206  */
 207 void qemu_clock_warp(QEMUClockType type);
 208
 209 /**
 210  * qemu_clock_register_reset_notifier:
 211  * @type: the clock type
 212  * @notifier: the notifier function
 213  *
 214  * Register a notifier function to call when the clock
 215  * concerned is reset.
 216  */
 217 void qemu_clock_register_reset_notifier(QEMUClockType type,
 218                                         Notifier *notifier);
 219
 220 /**
 221  * qemu_clock_unregister_reset_notifier:
 222  * @type: the clock type
 223  * @notifier: the notifier function
 224  *
 225  * Unregister a notifier function to call when the clock
 226  * concerned is reset.
 227  */
 228 void qemu_clock_unregister_reset_notifier(QEMUClockType type,
 229                                           Notifier *notifier);
 230
 231 /**
 232  * qemu_clock_run_timers:
 233  * @type: clock on which to operate
 234  *
 235  * Run all the timers associated with the default timer list
 236  * of a clock.
 237  *
 238  * Returns: true if any timer ran.
 239  */
 240 bool qemu_clock_run_timers(QEMUClockType type);
 241
 242 /**
 243  * qemu_clock_run_all_timers:
 244  *
 245  * Run all the timers associated with the default timer list
 246  * of every clock.
 247  *
 248  * Returns: true if any timer ran.
 249  */
 250 bool qemu_clock_run_all_timers(void);
 251
 252 /*
 253  * QEMUTimerList
 254  */
 255
 256 /**
 257  * timerlist_new:
 258  * @type: the clock type to associate with the timerlist
 259  * @cb: the callback to call on notification
 260  * @opaque: the opaque pointer to pass to the callback
 261  *
 262  * Create a new timerlist associated with the clock of
 263  * type @type.
 264  *
 265  * Returns: a pointer to the QEMUTimerList created
 266  */
 267 QEMUTimerList *timerlist_new(QEMUClockType type,
 268                              QEMUTimerListNotifyCB *cb, void *opaque);
 269
 270 /**
 271  * timerlist_free:
 272  * @timer_list: the timer list to free
 273  *
 274  * Frees a timer_list. It must have no active timers.
 275  */
 276 void timerlist_free(QEMUTimerList *timer_list);
 277
 278 /**
 279  * timerlist_has_timers:
 280  * @timer_list: the timer list to operate on
 281  *
 282  * Determine whether a timer list has active timers
 283  *
 284  * Note that this function should not be used when other threads also access
 285  * the timer list.  The return value may be outdated by the time it is acted
 286  * upon.
 287  *
 288  * Returns: true if the timer list has timers.
 289  */
 290 bool timerlist_has_timers(QEMUTimerList *timer_list);
 291
 292 /**
 293  * timerlist_expired:
 294  * @timer_list: the timer list to operate on
 295  *
 296  * Determine whether a timer list has any timers which
 297  * are expired.
 298  *
 299  * Returns: true if the timer list has timers which
 300  * have expired.
 301  */
 302 bool timerlist_expired(QEMUTimerList *timer_list);
 303
 304 /**
 305  * timerlist_deadline_ns:
 306  * @timer_list: the timer list to operate on
 307  *
 308  * Determine the deadline for a timer_list, i.e.
 309  * the number of nanoseconds until the first timer
 310  * expires. Return -1 if there are no timers.
 311  *
 312  * Returns: the number of nanoseconds until the earliest
 313  * timer expires -1 if none
 314  */
 315 int64_t timerlist_deadline_ns(QEMUTimerList *timer_list);
 316
 317 /**
 318  * timerlist_get_clock:
 319  * @timer_list: the timer list to operate on
 320  *
 321  * Determine the clock type associated with a timer list.
 322  *
 323  * Returns: the clock type associated with the
 324  * timer list.
 325  */
 326 QEMUClockType timerlist_get_clock(QEMUTimerList *timer_list);
 327
 328 /**
 329  * timerlist_run_timers:
 330  * @timer_list: the timer list to use
 331  *
 332  * Call all expired timers associated with the timer list.
 333  *
 334  * Returns: true if any timer expired
 335  */
 336 bool timerlist_run_timers(QEMUTimerList *timer_list);
 337
 338 /**
 339  * timerlist_notify:
 340  * @timer_list: the timer list to use
 341  *
 342  * call the notifier callback associated with the timer list.
 343  */
 344 void timerlist_notify(QEMUTimerList *timer_list);
 345
 346 /*
 347  * QEMUTimerListGroup
 348  */
 349
 350 /**
 351  * timerlistgroup_init:
 352  * @tlg: the timer list group
 353  * @cb: the callback to call when a notify is required
 354  * @opaque: the opaque pointer to be passed to the callback.
 355  *
 356  * Initialise a timer list group. This must already be
 357  * allocated in memory and zeroed. The notifier callback is
 358  * called whenever a clock in the timer list group is
 359  * reenabled or whenever a timer associated with any timer
 360  * list is modified. If @cb is specified as null, qemu_notify()
 361  * is used instead.
 362  */
 363 void timerlistgroup_init(QEMUTimerListGroup *tlg,
 364                          QEMUTimerListNotifyCB *cb, void *opaque);
 365
 366 /**
 367  * timerlistgroup_deinit:
 368  * @tlg: the timer list group
 369  *
 370  * Deinitialise a timer list group. This must already be
 371  * initialised. Note the memory is not freed.
 372  */
 373 void timerlistgroup_deinit(QEMUTimerListGroup *tlg);
 374
 375 /**
 376  * timerlistgroup_run_timers:
 377  * @tlg: the timer list group
 378  *
 379  * Run the timers associated with a timer list group.
 380  * This will run timers on multiple clocks.
 381  *
 382  * Returns: true if any timer callback ran
 383  */
 384 bool timerlistgroup_run_timers(QEMUTimerListGroup *tlg);
 385
 386 /**
 387  * timerlistgroup_deadline_ns:
 388  * @tlg: the timer list group
 389  *
 390  * Determine the deadline of the soonest timer to
 391  * expire associated with any timer list linked to
 392  * the timer list group. Only clocks suitable for
 393  * deadline calculation are included.
 394  *
 395  * Returns: the deadline in nanoseconds or -1 if no
 396  * timers are to expire.
 397  */
 398 int64_t timerlistgroup_deadline_ns(QEMUTimerListGroup *tlg);
 399
 400 /*
 401  * QEMUTimer
 402  */
 403
 404 /**
 405  * timer_init:
 406  * @ts: the timer to be initialised
 407  * @timer_list: the timer list to attach the timer to
 408  * @scale: the scale value for the tiemr
 409  * @cb: the callback to be called when the timer expires
 410  * @opaque: the opaque pointer to be passed to the callback
 411  *
 412  * Initialise a new timer and associate it with @timer_list.
 413  * The caller is responsible for allocating the memory.
 414  *
 415  * You need not call an explicit deinit call. Simply make
 416  * sure it is not on a list with timer_del.
 417  */
 418 void timer_init(QEMUTimer *ts,
 419                 QEMUTimerList *timer_list, int scale,
 420                 QEMUTimerCB *cb, void *opaque);
 421
 422 /**
 423  * timer_new_tl:
 424  * @timer_list: the timer list to attach the timer to
 425  * @scale: the scale value for the tiemr
 426  * @cb: the callback to be called when the timer expires
 427  * @opaque: the opaque pointer to be passed to the callback
 428  *
 429  * Creeate a new timer and associate it with @timer_list.
 430  * The memory is allocated by the function.
 431  *
 432  * This is not the preferred interface unless you know you
 433  * are going to call timer_free. Use timer_init instead.
 434  *
 435  * Returns: a pointer to the timer
 436  */
 437 static inline QEMUTimer *timer_new_tl(QEMUTimerList *timer_list,
 438                                       int scale,
 439                                       QEMUTimerCB *cb,
 440                                       void *opaque)
 441 {
 442     QEMUTimer *ts = g_malloc0(sizeof(QEMUTimer));
 443     timer_init(ts, timer_list, scale, cb, opaque);
 444     return ts;
 445 }
 446
 447 /**
 448  * timer_new:
 449  * @type: the clock type to use
 450  * @scale: the scale value for the tiemr
 451  * @cb: the callback to be called when the timer expires
 452  * @opaque: the opaque pointer to be passed to the callback
 453  *
 454  * Creeate a new timer and associate it with the default
 455  * timer list for the clock type @type.
 456  *
 457  * Returns: a pointer to the timer
 458  */
 459 static inline QEMUTimer *timer_new(QEMUClockType type, int scale,
 460                                    QEMUTimerCB *cb, void *opaque)
 461 {
 462     return timer_new_tl(main_loop_tlg.tl[type], scale, cb, opaque);
 463 }
 464
 465 /**
 466  * timer_new_ns:
 467  * @clock: the clock to associate with the timer
 468  * @callback: the callback to call when the timer expires
 469  * @opaque: the opaque pointer to pass to the callback
 470  *
 471  * Create a new timer with nanosecond scale on the default timer list
 472  * associated with the clock.
 473  *
 474  * Returns: a pointer to the newly created timer
 475  */
 476 static inline QEMUTimer *timer_new_ns(QEMUClockType type, QEMUTimerCB *cb,
 477                                       void *opaque)
 478 {
 479     return timer_new(type, SCALE_NS, cb, opaque);
 480 }
 481
 482 /**
 483  * timer_new_us:
 484  * @clock: the clock to associate with the timer
 485  * @callback: the callback to call when the timer expires
 486  * @opaque: the opaque pointer to pass to the callback
 487  *
 488  * Create a new timer with microsecond scale on the default timer list
 489  * associated with the clock.
 490  *
 491  * Returns: a pointer to the newly created timer
 492  */
 493 static inline QEMUTimer *timer_new_us(QEMUClockType type, QEMUTimerCB *cb,
 494                                       void *opaque)
 495 {
 496     return timer_new(type, SCALE_US, cb, opaque);
 497 }
 498
 499 /**
 500  * timer_new_ms:
 501  * @clock: the clock to associate with the timer
 502  * @callback: the callback to call when the timer expires
 503  * @opaque: the opaque pointer to pass to the callback
 504  *
 505  * Create a new timer with millisecond scale on the default timer list
 506  * associated with the clock.
 507  *
 508  * Returns: a pointer to the newly created timer
 509  */
 510 static inline QEMUTimer *timer_new_ms(QEMUClockType type, QEMUTimerCB *cb,
 511                                       void *opaque)
 512 {
 513     return timer_new(type, SCALE_MS, cb, opaque);
 514 }
 515
 516 /**
 517  * timer_free:
 518  * @ts: the timer
 519  *
 520  * Free a timer (it must not be on the active list)
 521  */
 522 void timer_free(QEMUTimer *ts);
 523
 524 /**
 525  * timer_del:
 526  * @ts: the timer
 527  *
 528  * Delete a timer from the active list.
 529  *
 530  * This function is thread-safe but the timer and its timer list must not be
 531  * freed while this function is running.
 532  */
 533 void timer_del(QEMUTimer *ts);
 534
 535 /**
 536  * timer_mod_ns:
 537  * @ts: the timer
 538  * @expire_time: the expiry time in nanoseconds
 539  *
 540  * Modify a timer to expire at @expire_time
 541  *
 542  * This function is thread-safe but the timer and its timer list must not be
 543  * freed while this function is running.
 544  */
 545 void timer_mod_ns(QEMUTimer *ts, int64_t expire_time);
 546
 547 /**
 548  * timer_mod_anticipate_ns:
 549  * @ts: the timer
 550  * @expire_time: the expiry time in nanoseconds
 551  *
 552  * Modify a timer to expire at @expire_time or the current time,
 553  * whichever comes earlier.
 554  *
 555  * This function is thread-safe but the timer and its timer list must not be
 556  * freed while this function is running.
 557  */
 558 void timer_mod_anticipate_ns(QEMUTimer *ts, int64_t expire_time);
 559
 560 /**
 561  * timer_mod:
 562  * @ts: the timer
 563  * @expire_time: the expire time in the units associated with the timer
 564  *
 565  * Modify a timer to expiry at @expire_time, taking into
 566  * account the scale associated with the timer.
 567  *
 568  * This function is thread-safe but the timer and its timer list must not be
 569  * freed while this function is running.
 570  */
 571 void timer_mod(QEMUTimer *ts, int64_t expire_timer);
 572
 573 /**
 574  * timer_mod_anticipate:
 575  * @ts: the timer
 576  * @expire_time: the expiry time in nanoseconds
 577  *
 578  * Modify a timer to expire at @expire_time or the current time, whichever
 579  * comes earlier, taking into account the scale associated with the timer.
 580  *
 581  * This function is thread-safe but the timer and its timer list must not be
 582  * freed while this function is running.
 583  */
 584 void timer_mod_anticipate(QEMUTimer *ts, int64_t expire_time);
 585
 586 /**
 587  * timer_pending:
 588  * @ts: the timer
 589  *
 590  * Determines whether a timer is pending (i.e. is on the
 591  * active list of timers, whether or not it has not yet expired).
 592  *
 593  * Returns: true if the timer is pending
 594  */
 595 bool timer_pending(QEMUTimer *ts);
 596
 597 /**
 598  * timer_expired:
 599  * @ts: the timer
 600  *
 601  * Determines whether a timer has expired.
 602  *
 603  * Returns: true if the timer has expired
 604  */
 605 bool timer_expired(QEMUTimer *timer_head, int64_t current_time);
 606
 607 /**
 608  * timer_expire_time_ns:
 609  * @ts: the timer
 610  *
 611  * Determine the expiry time of a timer
 612  *
 613  * Returns: the expiry time in nanoseconds
 614  */
 615 uint64_t timer_expire_time_ns(QEMUTimer *ts);
 616
 617 /**
 618  * timer_get:
 619  * @f: the file
 620  * @ts: the timer
 621  *
 622  * Read a timer @ts from a file @f
 623  */
 624 void timer_get(QEMUFile *f, QEMUTimer *ts);
 625
 626 /**
 627  * timer_put:
 628  * @f: the file
 629  * @ts: the timer
 630  */
 631 void timer_put(QEMUFile *f, QEMUTimer *ts);
 632
 633 /*
 634  * General utility functions
 635  */
 636
 637 /**
 638  * qemu_timeout_ns_to_ms:
 639  * @ns: nanosecond timeout value
 640  *
 641  * Convert a nanosecond timeout value (or -1) to
 642  * a millisecond value (or -1), always rounding up.
 643  *
 644  * Returns: millisecond timeout value
 645  */
 646 int qemu_timeout_ns_to_ms(int64_t ns);
 647
 648 /**
 649  * qemu_poll_ns:
 650  * @fds: Array of file descriptors
 651  * @nfds: number of file descriptors
 652  * @timeout: timeout in nanoseconds
 653  *
 654  * Perform a poll like g_poll but with a timeout in nanoseconds.
 655  * See g_poll documentation for further details.
 656  *
 657  * Returns: number of fds ready
 658  */
 659 int qemu_poll_ns(GPollFD *fds, guint nfds, int64_t timeout);
 660
 661 /**
 662  * qemu_soonest_timeout:
 663  * @timeout1: first timeout in nanoseconds (or -1 for infinite)
 664  * @timeout2: second timeout in nanoseconds (or -1 for infinite)
 665  *
 666  * Calculates the soonest of two timeout values. -1 means infinite, which
 667  * is later than any other value.
 668  *
 669  * Returns: soonest timeout value in nanoseconds (or -1 for infinite)
 670  */
 671 static inline int64_t qemu_soonest_timeout(int64_t timeout1, int64_t timeout2)
 672 {
 673     /* we can abuse the fact that -1 (which means infinite) is a maximal
 674      * value when cast to unsigned. As this is disgusting, it's kept in
 675      * one inline function.
 676      */
 677     return ((uint64_t) timeout1 < (uint64_t) timeout2) ? timeout1 : timeout2;
 678 }
 679
 680 /**
 681  * initclocks:
 682  *
 683  * Initialise the clock & timer infrastructure
 684  */
 685 void init_clocks(void);
 686
 687 int64_t cpu_get_ticks(void);
 688 /* Caller must hold BQL */
 689 void cpu_enable_ticks(void);
 690 /* Caller must hold BQL */
 691 void cpu_disable_ticks(void);
 692
 693 static inline int64_t get_ticks_per_sec(void)
 694 {
 695     return 1000000000LL;
 696 }
 697
 698 /*
 699  * Low level clock functions
 700  */
 701
 702 /* real time host monotonic timer */
 703 static inline int64_t get_clock_realtime(void)
 704 {
 705     struct timeval tv;
 706
 707     gettimeofday(&tv, NULL);
 708     return tv.tv_sec * 1000000000LL + (tv.tv_usec * 1000);
 709 }
 710
 711 /* Warning: don't insert tracepoints into these functions, they are
 712    also used by simpletrace backend and tracepoints would cause
 713    an infinite recursion! */
 714 #ifdef _WIN32
 715 extern int64_t clock_freq;
 716
 717 static inline int64_t get_clock(void)
 718 {
 719     LARGE_INTEGER ti;
 720     QueryPerformanceCounter(&ti);
 721     return muldiv64(ti.QuadPart, get_ticks_per_sec(), clock_freq);
 722 }
 723
 724 #else
 725
 726 extern int use_rt_clock;
 727
 728 static inline int64_t get_clock(void)
 729 {
 730 #ifdef CLOCK_MONOTONIC
 731     if (use_rt_clock) {
 732         struct timespec ts;
 733         clock_gettime(CLOCK_MONOTONIC, &ts);
 734         return ts.tv_sec * 1000000000LL + ts.tv_nsec;
 735     } else
 736 #endif
 737     {
 738         /* XXX: using gettimeofday leads to problems if the date
 739            changes, so it should be avoided. */
 740         return get_clock_realtime();
 741     }
 742 }
 743 #endif
 744
 745 /* icount */
 746 int64_t cpu_get_icount(void);
 747 int64_t cpu_get_clock(void);
 748
 749 /*******************************************/
 750 /* host CPU ticks (if available) */
 751
 752 #if defined(_ARCH_PPC)
 753
 754 static inline int64_t cpu_get_real_ticks(void)
 755 {
 756     int64_t retval;
 757 #ifdef _ARCH_PPC64
 758     /* This reads timebase in one 64bit go and includes Cell workaround from:
 759        http://ozlabs.org/pipermail/linuxppc-dev/2006-October/027052.html
 760     */
 761     __asm__ __volatile__ ("mftb    %0\n\t"
 762                           "cmpwi   %0,0\n\t"
 763                           "beq-    $-8"
 764                           : "=r" (retval));
 765 #else
 766     /* http://ozlabs.org/pipermail/linuxppc-dev/1999-October/003889.html */
 767     unsigned long junk;
 768     __asm__ __volatile__ ("mfspr   %1,269\n\t"  /* mftbu */
 769                           "mfspr   %L0,268\n\t" /* mftb */
 770                           "mfspr   %0,269\n\t"  /* mftbu */
 771                           "cmpw    %0,%1\n\t"
 772                           "bne     $-16"
 773                           : "=r" (retval), "=r" (junk));
 774 #endif
 775     return retval;
 776 }
 777
 778 #elif defined(__i386__)
 779
 780 static inline int64_t cpu_get_real_ticks(void)
 781 {
 782     int64_t val;
 783     asm volatile ("rdtsc" : "=A" (val));
 784     return val;
 785 }
 786
 787 #elif defined(__x86_64__)
 788
 789 static inline int64_t cpu_get_real_ticks(void)
 790 {
 791     uint32_t low,high;
 792     int64_t val;
 793     asm volatile("rdtsc" : "=a" (low), "=d" (high));
 794     val = high;
 795     val <<= 32;
 796     val |= low;
 797     return val;
 798 }
 799
 800 #elif defined(__hppa__)
 801
 802 static inline int64_t cpu_get_real_ticks(void)
 803 {
 804     int val;
 805     asm volatile ("mfctl %%cr16, %0" : "=r"(val));
 806     return val;
 807 }
 808
 809 #elif defined(__ia64)
 810
 811 static inline int64_t cpu_get_real_ticks(void)
 812 {
 813     int64_t val;
 814     asm volatile ("mov %0 = ar.itc" : "=r"(val) :: "memory");
 815     return val;
 816 }
 817
 818 #elif defined(__s390__)
 819
 820 static inline int64_t cpu_get_real_ticks(void)
 821 {
 822     int64_t val;
 823     asm volatile("stck 0(%1)" : "=m" (val) : "a" (&val) : "cc");
 824     return val;
 825 }
 826
 827 #elif defined(__sparc__)
 828
 829 static inline int64_t cpu_get_real_ticks (void)
 830 {
 831 #if defined(_LP64)
 832     uint64_t        rval;
 833     asm volatile("rd %%tick,%0" : "=r"(rval));
 834     return rval;
 835 #else
 836     /* We need an %o or %g register for this.  For recent enough gcc
 837        there is an "h" constraint for that.  Don't bother with that.  */
 838     union {
 839         uint64_t i64;
 840         struct {
 841             uint32_t high;
 842             uint32_t low;
 843         }       i32;
 844     } rval;
 845     asm volatile("rd %%tick,%%g1; srlx %%g1,32,%0; mov %%g1,%1"
 846                  : "=r"(rval.i32.high), "=r"(rval.i32.low) : : "g1");
 847     return rval.i64;
 848 #endif
 849 }
 850
 851 #elif defined(__mips__) && \
 852     ((defined(__mips_isa_rev) && __mips_isa_rev >= 2) || defined(__linux__))
 853 /*
 854  * binutils wants to use rdhwr only on mips32r2
 855  * but as linux kernel emulate it, it's fine
 856  * to use it.
 857  *
 858  */
 859 #define MIPS_RDHWR(rd, value) {                         \
 860         __asm__ __volatile__ (".set   push\n\t"         \
 861                               ".set mips32r2\n\t"       \
 862                               "rdhwr  %0, "rd"\n\t"     \
 863                               ".set   pop"              \
 864                               : "=r" (value));          \
 865     }
 866
 867 static inline int64_t cpu_get_real_ticks(void)
 868 {
 869     /* On kernels >= 2.6.25 rdhwr <reg>, $2 and $3 are emulated */
 870     uint32_t count;
 871     static uint32_t cyc_per_count = 0;
 872
 873     if (!cyc_per_count) {
 874         MIPS_RDHWR("$3", cyc_per_count);
 875     }
 876
 877     MIPS_RDHWR("$2", count);
 878     return (int64_t)(count * cyc_per_count);
 879 }
 880
 881 #elif defined(__alpha__)
 882
 883 static inline int64_t cpu_get_real_ticks(void)
 884 {
 885     uint64_t cc;
 886     uint32_t cur, ofs;
 887
 888     asm volatile("rpcc %0" : "=r"(cc));
 889     cur = cc;
 890     ofs = cc >> 32;
 891     return cur - ofs;
 892 }
 893
 894 #else
 895 /* The host CPU doesn't have an easily accessible cycle counter.
 896    Just return a monotonically increasing value.  This will be
 897    totally wrong, but hopefully better than nothing.  */
 898 static inline int64_t cpu_get_real_ticks (void)
 899 {
 900     static int64_t ticks = 0;
 901     return ticks++;
 902 }
 903 #endif
 904
 905 #ifdef CONFIG_PROFILER
 906 static inline int64_t profile_getclock(void)
 907 {
 908     return cpu_get_real_ticks();
 909 }
 910
 911 extern int64_t qemu_time, qemu_time_start;
 912 extern int64_t tlb_flush_time;
 913 extern int64_t dev_time;
 914 #endif
 915
 916 #endif