kstat_runq_exit(9F)

NAME

     kstat_queue,      kstat_waitq_enter,       kstat_waitq_exit,
     kstat_runq_enter,    kstat_runq_exit,   kstat_waitq_to_runq,
     kstat_runq_back_to_waitq - update I/O kstat statistics

SYNOPSIS

     #include <sys/types.h>
     #include <sys/kstat.h>

     void kstat_waitq_enter(kstat_io_t *kiop);

     void kstat_waitq_exit(kstat_io_t *kiop);

     void kstat_runq_enter(kstat_io_t *kiop);

     void kstat_runq_exit(kstat_io_t *kiop);

     void kstat_waitq_to_runq(kstat_io_t *kiop);

     void kstat_runq_back_to_waitq(kstat_io_t *kiop);

INTERFACE LEVEL

     Solaris DDI specific (Solaris DDI)

PARAMETERS

     kiop  Pointer to a kstat_io(9S) structure.

DESCRIPTION

     A large number of I/O subsystems have  at  least  two  basic
     "lists"  (or  queues)  of  transactions they manage: one for
     transactions that have been accepted for processing but  for
     which  processing has yet to begin, and one for transactions
     which are actively being processed (but not done). For  this
     reason,  two cumulative time statistics are kept: wait (pre-
     service) time, and run (service) time.

     The kstat_queue() family of  functions  manage  these  times
     based  on  the transitions between the driver wait queue and
     run queue.

          kstat_waitq_enter()
                kstat_waitq_enter()  should  be  called  when   a
                request  arrives and is placed into a pre-service
                state   (such   as   just   prior   to    calling
                disksort(9F)).

          kstat_waitq_exit()
                kstat_waitq_exit() should be used when a  request
                is  removed  from its pre-service state. (such as
                just prior to calling  the  driver's  start  rou-
                tine).

          kstat_runq_enter()
                kstat_runq_enter() is also called when a  request
                is  placed  in  its  service state (just prior to
                calling the driver's  start  routine,  but  after
                kstat_waitq_exit()).

          kstat_runq_exit()
                kstat_runq_exit()  is  used  when  a  request  is
                removed  from  its  service  state (just prior to
                calling biodone(9F)).

          kstat_waitq_to_runq()
                kstat_waitq_to_runq() transitions a request  from
                the  wait  queue to the run queue. This is useful
                wherever the driver would have  normally  done  a
                kstat_waitq_exit()   followed   by   a   call  to
                kstat_runq_enter().

          kstat_runq_back_to_waitq()
                kstat_runq_back_to_waitq() transitions a  request
                from  the  run queue back to the wait queue. This
                may be necessary in some cases (write  throttling
                is an example).

RETURN VALUES

     None.

CONTEXT

     kstat_create() can be called from user or kernel context.

WARNINGS

     These transitions must be protected by holding  the  kstat's
     ks_lock,  and  must  be completely accurate (all transitions
     are recorded). Forgetting a  transition  may,  for  example,
     make an idle disk appear 100% busy.

SEE ALSO

     biodone(9F),         disksort(9F),         kstat_create(9F),
     kstat_delete(9F),      kstat_named_init(9F),      kstat(9S),
     kstat_io(9S)

     Writing Device Drivers