aio_proc_thread_pct(5) File Formats Manual aio_proc_thread_pct(5)
aio_proc_thread_pct - percentage of all process threads allowed in AIO pool
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(5),
aio_proc_thread_pct(5), aio_req_per_thread(5), and aio_monitor_run_sec(5). Please see individual manpages for details on each of these
The tunable specifies, on a per-process basis, the percentage of threads that can be used by the POSIX AIO system as kernel threads for
issuing I/Os. The percentage is taken as a percentage of which is the upper bound on the number of threads a process may have.
This tunable interacts with in the following way: the maximum number of threads used for AIO will be the smaller of the two values defined
by the two tunables; i.e.:
This allows the number of AIO threads to vary dynamically with but to always be bound by an absolute limit of
Who Is Expected to Change This Tunable?
System administrators that run applications requiring heavy usage of POSIX AIO to filesystems.
Restrictions on Changing
This tunables 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 tunable
When Should the Value of This Tunable Be Raised?
should be raised for applications that do not use very many threads for their own work, but desire high performance from the POSIX AIO sub-
What Are the Side Effects of Raising the Value of This Tunable?
Some applications that use POSIX AIO but also require a large number of threads may find that they are unable to create new threads,
because the POSIX AIO thread pool ends up using too many of a process' allowable threads.
In addition, using a larger number of kernel threads might lead to increased CPU utilization.
When Should the Value of This Tunable Be Lowered?
should be lowered when POSIX AIO performance is acceptable but applications using POSIX AIO are seeing errors when trying to create new
threads for other work.
What Are the Side Effects of Lowering the Value of This Tunable?
By ultimately reducing the number of threads available to handle POSIX AIO requests, overall I/O throughput of the POSIX AIO subsystem
could be reduced.
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. This allows a hard limit to
be imposed, regardless of what value happens to take.
defines the desired relationship between the number of POSIX AIO kernel threads and the number of I/Os to be serviced.
defines how often (in seconds) the AIO thread mechanism will monitor itself for adherence to the constraints defined by the tunables above.
All HP-UX kernel tunable parameters are release specific. This parameter 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 values. For information about the effects of installation on tun-
able values, 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.
kctune(1M), sam(1M), gettune(2), settune(2), aio_proc_threads(5), aio_req_per_thread(5), aio_monitor_run_sec(5).
Tunable Kernel Parameters aio_proc_thread_pct(5)