illumos: manual page: kstat_runq

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

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.