kstat_waitq_to_runq man page on Solaris

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kstat_queue(9F)		 Kernel Functions for Drivers	       kstat_queue(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 routine).

       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 ser‐
	   vice 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 nor‐
	   mally  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

SunOS 5.10			  4 Apr 1994		       kstat_queue(9F)
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