aio_monitor_run_sec(5)aio_monitor_run_sec(5)NAMEaio_monitor_run_sec - frequency of AIO thread pool monitor execution
The implementation of POSIX AIO on HP-UX uses kernel threads to perform
I/Os to filesystems that do not directly support true asynchronous I/O.
(This distinction is transparent to the user.) The kernel threads are
organized into worker-thread pools (called AIO thread pools) created on
a per-process basis. Since a thread pool mechanism for I/Os introduces
a variety of trade-offs concerning utilization of CPU time vs. I/O
resources, four dynamic tunables are available to customize the behav‐
ior of this thread pool: and Please see individual manpages for details
on each of these tunables.
The tunable specifies how frequently a process' AIO thread pool will be
monitored. Monitoring involves making decisions about growing or
shrinking the AIO thread pool based on the constraints specified by and
Note that although the AIO thread pool can grow both on its own (as new
I/Os are issued) or as a result of the monitoring mechanism, the moni‐
toring mechanism is the primary method by which the thread pool can
shrink. So this tunable effectively determines how quickly the AIO
thread pool will adapt itself to a given I/O load.
Who Is Expected to Change This Tunable?
System administrators that run applications requiring heavy usage of
POSIX AIO to filesystems.
Restrictions on Changing
This tunable is dynamic. Changes to to this tunable take effect imme‐
diately for new processes started after the change. They also impact
existing processes, but the speed with which the changes propagate to
running processes is determined by the former value of
When Should the Value of This Tunable Be Raised?
should be raised for applications that have steady I/O loads for which
POSIX AIO would rarely need to adapt. Another possibility is applica‐
tions with bursty or periodic I/O loads, that want POSIX AIO to main‐
tain a larger thread pool through periods of decreased I/O activity (to
be ready for busier periods). This can be accomplished by increasing
this tunable to reduce the frequency of AIO monitor updates.
What Are the Side Effects of Raising the Value of This Tunable?
Increasing this tunable will reduce the speed with which the POSIX AIO
thread pool mechanism adapts itself to changing I/O loads. This could
cause slightly reduced performance when applications first begin to
issue POSIX AIOs.
When Should the Value of This Tunable Be Lowered?
should be lowered when applications want to increase the speed with
which the POSIX AIO thread pool adapts itself to I/O loads. This
should generally maximize performance, except in the case of bursty I/O
loads, or I/O loads with periodic peaks, for which a slower adaptation
may be desirable.
What Are the Side Effects of Lowering the Value of This Tunable?
The POSIX AIO thread pool will adjust more quickly to changing I/O
loads, so new threads will be spawned more quickly for new I/Os, and
threads will be killed more quickly as I/O loads decrease. Except for
bursty or periodic I/O loads, this should maximize performance.
What Other Tunables Should Be Changed at the Same Time as This One?
interacts with this tunable by setting a strict limit on the number of
threads that can be used for POSIX AIO.
interacts with this tunable by setting a limit on the number of threads
that can be used for POSIX_AIO, but does so based on a percentage of
the maximum number of allowable process threads. This allows the AIO
thread pools to respond dynamically to changes in
defines the desired relationship between the number of POSIX AIO kernel
threads and the number of I/Os to be serviced.
All HP-UX kernel tunable parameters are release specific. This parame‐
ter may be removed or have its meaning changed in future releases of
Installation of optional kernel software, from HP or other vendors, may
cause changes to tunable parameter values. After installation, some
tunable parameters may no longer be at the default or recommended val‐
ues. For information about the effects of installation on tunable val‐
ues, consult the documentation for the kernel software being installed.
For information about optional kernel software that was factory
installed on your system, see at
was developed by HP.
SEE ALSOkctune(1M), sam(1M), gettune(2), settune(2), aio_proc_threads(5),
Tunable Kernel Parameters aio_monitor_run_sec(5)