man/man9f/kstat_queue.9f

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 KSTAT_QUEUE 9F "Aug 18, 2019"
 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
illumos DDI specific (illumos 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 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
The kstat_queue() family of functions 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