HP-UX Reference (11i v2 04/09) - 5 Miscellaneous Topics (vol 9)

i
ioforw_timeout(5) ioforw_timeout(5)
(Tunable Kernel Parameters)
NAME
ioforw_timeout - enable timeout in I/O forwarding
VALUES
Failsafe
0 (off)
Default
0 (off)
Allowed values
0 (off) or 1 (on)
Recommended values
0 (off)
DESCRIPTION
With I/O forwarding, the drivers’ strategy routine forwards the I/O requests to a processor that is
configured to handle the I/O completion interrupts from the device. I/O forwarding queues these requests
in a per processor queue and handles them in a low priority interrupt context. In case of large number of
requests, I/O forwarding may starve processes scheduled on the processor.
When the tunable
ioforw_timeout
is set to 1, I/O forwarding times out periodically to let the
processes execute. This is important when the system has time sensitive processes that may flag an error
condition in the system resulting in the generation of unnecessary correction triggers. Since a timeout is
introduced in I/O forwarding, there may be a loss in I/O throughput.
Who Is Expected to Change This Tunable?
Only HP Field engineers should change the value of this tunable.
Restrictions on Changing
Changes to this tunable take effect immediately.
When Should the Tunable Be Turned On?
This tunable should be turned on if a time critical process times out in the presence of heavy I/O.
What Are the Side Effects of Turning the Tunable On?
As the timeout is introduced in I/O forwarding request processing, I/O throughput of the system may be
reduced.
What Other Tunables Should Be Changed at the Same Time?
This tunable is independent of other tunables.
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 parame-
ter 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
ioforw_timeout was developed by HP.
SEE ALSO
kctune(1M), kcweb(1M).
Section 5−−152 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: September 2004