common/os/cyclic.c

126  *      cyclic_softint()     <-- CY_LOCK/LOW_LEVEL soft interrupt entry point
317  *  cyclic subsystem's soft interrupt handler, cyclic_softint(), we repeatedly
324  *  level, cyclic_softint() must be able to quickly determine which cyclics
333  *  cypc_prodndx.  The consumer (cyclic_softint() running at either
341  *  cyclic_softint() only consumes a cyclic after it has decremented the
381  *  cyclic_expire() executing at CY_HIGH_LEVEL and cyclic_softint() executing
382  *  at one of CY_LOCK_LEVEL or CY_LOW_LEVEL), forcing cyclic_softint() to raise
391  *  and cyclic_softint() code paths to be lock-free.
395  *  cyclic_softint(), their actions on the producer/consumer buffer appear
399  *  For cyclic_softint(), however, lock-free execution requires more delicacy.
400  *  When cyclic_softint() discovers a cyclic in the producer/consumer buffer,
404  *  If the compare&swap operation succeeds, cyclic_softint() behaves
408  *       cyclic_softint() increments the cypc_consndx and checks for more
412  *       to be done on the cyclic; cyclic_softint() calls the cyclic handler
415  *  If the compare&swap operation fails, cyclic_softint() knows that
418  *  operation, below).  cyclic_softint() thus reloads cy_pend, and re-attempts
424  *  most once.  This leads to a critical constraint on cyclic_softint(),
426  *  cy_pend to zero, cyclic_softint() must _not_ re-examine the consumed
427  *  cyclic.  In part to obey this constraint, cyclic_softint() calls the
457  *  interrupted cyclic_softint() in the middle of consumption. To resize the
460  *  and a soft buffer (the buffer from which cyclic_softint() is consuming).
467  *  then posts a CY_LOCK_LEVEL soft interrupt, landing in cyclic_softint().
469  *  As under normal operation, cyclic_softint() will consume cyclics from
471  *  cyclic_softint() will see that the hard buffer has changed.  At that time,
472  *  cyclic_softint() will change its soft buffer to point to the hard buffer,
475  *  After the new buffer is drained, cyclic_softint() will determine if both
477  *  cyclic_softint() will post on the semaphore cyp_modify_wait.  If not, a
482  *  sema_p() in cyclic_expand() and the sema_v() in cyclic_softint()).  This
489  *  step addresses the problem of a cyclic_softint() attempting to decrement
491  *  cyclic_softint() has already called the handler by the time cy_pend is
495  *  cyclic_softint() attempts to compare&swap on the cy_pend count, it will
496  *  fail and recognize that the count has been zeroed.  cyclic_softint() will
503  *  allow optimization for the cyclic_fire()/cyclic_expire()/cyclic_softint()
525  *  The cy_pend count is decremented in cyclic_softint() after the cyclic
530  *  until cyclic_softint() has finished calling the cyclic handler.  To let
531  *  cyclic_softint() know that this cyclic has been removed, we zero the
532  *  cy_pend count.  This will cause cyclic_softint()'s compare&swap to fail.
533  *  When cyclic_softint() sees the zero cy_pend count, it knows that it's been
1049 	 * to account for the handler call in cyclic_softint().
1068  *  cyclic_softint(cpu_t *cpu, cyc_level_t level)
1072  *    cyclic_softint() is the cyclic subsystem's CY_LOCK_LEVEL and CY_LOW_LEVEL
1077  *    The first argument to cyclic_softint() is the CPU on which the interrupt
1078  *    is executing; backends must call into cyclic_softint() on the specified
1082  *    cyclic_softint() will call the handlers for cyclics pending at the
1083  *    specified level.  cyclic_softint() will not return until all pending
1086  *    may therefore prolong cyclic_softint().
1088  *    cyclic_softint() never disables interrupts, and, if neither a
1090  *    lock-free.  This assures that in the common case, cyclic_softint()
1092  *    cyclic_add() or cyclic_remove() is pending, cyclic_softint() may grab
1095  *    While cyclic_softint() is designed for bounded latency, it is obviously
1097  *    arbitrarily, callers of cyclic_softint() should not rely upon
1100  *    cyclic_softint() may be called spuriously without ill effect.
1109  *    CY_LOCK_LEVEL or CY_LOW_LEVEL.  The level passed to cyclic_softint()
1116 cyclic_softint(cpu_t *c, cyc_level_t level)