aio_req_per_thread man page on HP-UX

Man page or keyword search:  
man Server   10987 pages
apropos Keyword Search (all sections)
Output format
HP-UX logo
[printable version]

aio_req_per_thread(5)					 aio_req_per_thread(5)

       aio_req_per_thread  -  desirable	 ratio	between	 number of pending AIO
       requests and servicing threads

   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 desirable ratio
       between the number of pending POSIX AIO	requests  and  the  number  of
       threads in the AIO thread pool.

       The number of threads in the AIO thread pool is bounded by the tunables
       and but the tunable determines how the AIO thread pool  behaves	within
       that  bound.  determines how much the AIO thread pool grows as the num‐
       ber of outstanding AIO requests grows, by defining how many  I/Os  each
       thread will be responsible for.

   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 want to limit the number of
       threads used by the POSIX AIO subsystem.	 Applications would want to do
       this to either free up more process threads for other work, or to limit
       the level of concurrency inside POSIX AIO, perhaps to  reduce  load  on
       physically limited I/O devices.

   What Are the Side Effects of Raising the Value of This Tunable?
       By allowing less threads for POSIX AIO requests, concurrency is reduced
       and AIO I/O requests will have to wait longer for servicing.  This  can
       result  in  increased latency and reduced POSIX AIO performance on sys‐
       tems whose I/O stack could otherwise  handle  heavier  loads.   On  the
       other hand, less threads per request can result in less context switch‐
       ing, reducing the CPU utilization of POSIX AIO.

   When Should the Value of This Tunable Be Lowered?
       should be lowered when applications want to  maximize  the  concurrency
       and  performance	 of  POSIX  AIO requests.  This should be done when an
       application does not need a large number of threads for other work.

   What Are the Side Effects of Lowering the Value of This Tunable?
       Lowering this tunable results in more threads being used by  POSIX  AIO
       to  handle  I/O	requests,  which  could	 increase CPU usage and use up
       threads that applications might need for	 other	work.	On  the	 other
       hand, POSIX AIO performance should increase.

   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	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_threads(5),
       aio_proc_thread_pct(5), aio_monitor_run_sec(5).

			   Tunable Kernel Parameters	 aio_req_per_thread(5)

List of man pages available for HP-UX

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net