aio_proc_threads man page on HP-UX

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aio_proc_threads(5)					   aio_proc_threads(5)

       aio_proc_threads	 -  maximum  number  of process threads allowed in AIO

   Allowed values
   Recommended values
       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: aio_proc_threads(5), aio_proc_thread_pct(5),
       aio_req_per_thread(5), and aio_monitor_run_sec(5).  Please see individ‐
       ual manpages for details on each of these tunables.

       The  tunable  specifies,	 on a per-process basis, the maximum number of
       process threads that can be used by the	POSIX  AIO  system  as	kernel
       threads for issuing I/Os.

       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  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 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 subsys‐

   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.	 (This
       could happen if 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 applica‐
       tions  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 limit on  the  number  of  AIO
       threads	based  on  a  percentage  of  the  maximum number of allowable
       process threads.	 This allows the AIO thread pools to  respond  dynami‐
       cally to changes in

       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 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.

       kctune(1M),  sam(1M),  gettune(2),  settune(2), aio_proc_thread_pct(5),
       aio_req_per_thread(5), aio_monitor_run_sec(5).

			   Tunable Kernel Parameters	   aio_proc_threads(5)

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