Enhancements to IO Forwarding

IO Forwarding is a functionality available in HP-UX, from 10.x onwards, by which I/O requests are forwarded to the processor assigned to handle the associated device interrupt, so as to eliminate cache-to-cache synchronization and thereby improve performance.

The following enhancements to IO Forwarding in HP-UX integrate with Detect & Strobe functionality. (For information on Detect & Strobe, see “Detect and Strobe”.)

Summary of Change

What’s New for Customers Migrating from HP-UX 11i v1 September 2005?

These enhancements include:

HP-UX 11i v3 no longer includes the tunable for ioforw_timeout, which was introduced as part of a patch.
IO Forwarding has been brought under the purview of Detect and Strobe.

What’s New for Customers Migrating from HP-UX 11i v2 June 2006?

HP-UX 11i v3 no longer includes the tunable for ioforw_timeout.
IO Forwarding has been brought under the purview of Detect and Strobe.

Impact

When Detect & Strobe is enabled, you see an improvement in overall system performance when the system is experiencing heavy IO Forwarding activity. This could lead to a slight drop in the rate of IO request processing and affect the throughput of high frequency interrupt generating IO-bound jobs.

Compatibility

Retraction of tunable for ioforw_timeout. Enablement of the throttling mechanism by default (interrupt throttling accomplished using Detect & Strobe).

Performance

You may experience some performance degradation for IO bound processes only with extremely high rate of interrupt generation. However, you should see overall system performance improvement under heavy interrupt activity.

Documentation

Beyond this section, there is no separate documentation for IO Forwarding in HP-UX 11i v3. For information about IO Forwarding when it was first introduced (during the HP-UX v10.0 to 10.30 era), see the following:

Obsolescence

This product was first developed as an enhancement over HP-UX 11i v1, integrated into the pre-release base kernel code in HP-UX 11i v2, and added into the pre-release base kernel code in HP-UX 11i v3. There are no current plans for obsolescence.