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IO_PRCPU_BITMAP is a bitmap system parameter that specifies which CPUs are available for use as a Fast Path preferred CPU on Alpha and Integrity servers.

This parameter is a bitmap representing up to 1024 CPUs. Each bit set in this bitmap indicates that the corresponding CPU is available for use as a Fast Path preferred CPU. IO_PRCPU_BITMAP defaults to all bits set. (CPU 0 through CPU 1023 are all enabled for Fast Path port assignment.)

You might want to disable the primary CPU from serving as a preferred CPU by leaving its bit clear in IO_PRCPU_BITMAP, which reserves the primary CPU for non-Fast Path IO operations to use.

To change the value of IO_PRCPU_BITMAP in SYSBOOT or SYSGEN, specify a list of individual bits or contiguous groups of bits. For example:


This command sets bits 0, 5, 17, 18, 19, 20, and 21 in the bitmap and clears all other bits.

Changing the value of IO_PRCPU_BITMAP causes the FASTPATH_SERVER process to run the automatic assignment algorithm that spreads Fast Path ports evenly among the new set of usable CPUs.

See also

This parameter replaces IO_PREFER_CPU.