aio_monitor_run

NAME

aio_monitor_run_sec — frequency of AIO thread pool monitor execution (in seconds)

VALUES

Failsafe

2

Default

30

Allowed values

1-60

Recommended values

1-60

DESCRIPTION

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 behavior of this thread pool: aio_proc_threads, aio_proc_thread_pct, aio_req_per_thread, and aio_monitor_run_sec. Please see individual manpages for details on each of these tunables.

The tunable aio_monitor_run_sec 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 aio_proc_threads, aio_proc_thread_pct, and aio_req_per_thread.

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 monitoring 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 immediately 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 aio_monitor_run_sec.

When Should the Value of This Tunable Be Raised?

aio_monitor_run_sec should be raised for applications that have steady I/O loads for which POSIX AIO would rarely need to adapt. Another possibility is applications with bursty or periodic I/O loads, that want POSIX AIO to maintain 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?

aio_monitor_run_sec 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?

aio_proc_threads interacts with this tunable by setting a strict limit on the number of threads that can be used for POSIX AIO.

aio_proc_thread_pct 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 max_thread_proc.

aio_req_per_thread defines the desired relationship between the number of POSIX AIO kernel threads and the number of I/Os to be serviced.

WARNINGS

All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of HP-UX.

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 values. For information about the effects of installation on tunable values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see HP-UX Release Notes at http://docs.hp.com.

AUTHOR

aio_monitor_run_sec was developed by HP.

aio_monitor_run_sec(5)

Technical documentation

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