Tribblix: manual page: kstat

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.