Operating System - OpenVMS
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IO_PREFER_CPUS not behaving as expected.

Christof Schoeman
Frequent Advisor

IO_PREFER_CPUS not behaving as expected.


Even though I've set IO_PREFER_CPUS to FFFC on this 16-CPU GS160, it still appears as if only CPU-0 and CPU-5 are handling all the interrupts.

CPU-0 is probably handling network I/Os, and CPU-5 the disk I/Os. But what about the rest? Why aren't they handling any interrupts?

Hope you can help.
John Gillings
Honored Contributor

Re: IO_PREFER_CPUS not behaving as expected.


IO_PREFER_CPUS controls the set of CPUs *available* for Fast Path I/O processing, it does not, in itself enable fast path.

SYSGEN parameters FAST_PATH and FAST_PATH_PORTS also need to be set correctly for your version and hardware (in recent versions they are enabled by default).

Finally, the selected devices themselves need to be enabled with


See the HP I/O User's Reference Manual for more detail in configuring Fast Path.
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