Current and preferred processor compatibility modes

The processor compatibility mode in which the logical partition currently operates is the current processor compatibility mode of the logical partition. The preferred processor compatibility mode of a logical partition is the mode in which you want the logical partition to operate.

The hypervisor sets the current processor compatibility mode for a logical partition by using the following information:

• The processor features supported by the operating environment running in the logical partition.
• The preferred processor compatibility mode that you specify.

When you activate the logical partition, the hypervisor checks the preferred processor compatibility mode and determines whether the operating environment supports that mode. If the operating environment supports the preferred processor compatibility mode, the hypervisor assigns the logical partition the preferred processor compatibility mode. If the operating environment does not support the preferred processor compatibility mode, the hypervisor assigns the logical partition the most fully featured processor compatibility mode that is supported by the operating environment.

The following table describes when each processor compatibility mode can be current mode or the preferred mode.

The following table shows the current and preferred processor compatibility modes supported on each server type.

The preferred processor compatibility mode is the highest mode that the hypervisor can assign to a logical partition. If the operating environment installed in the logical partition does not support the preferred mode, the hypervisor can set the current mode to a lower mode than the preferred mode, but it cannot set the current mode to a higher mode than the preferred mode. For example, assume that a logical partition runs on a POWER8 processor-based server and you specify POWER8 as the preferred mode. The operating environment installed in the logical partition does not support the POWER8 processor capabilities, but it does support the POWER7 processor capabilities. When you activate the logical partition, the hypervisor assigns the POWER7 processor compatibility mode as the current mode for the logical partition because the POWER7 mode is the most fully featured mode that the operating environment supports and it is a lower mode than the preferred mode of POWER8.

You cannot dynamically change the current processor compatibility of a logical partition. To change the current processor compatibility mode, you must change the preferred processor compatibility mode, shut down the logical partition, and restart the logical partition. The hypervisor attempts to set the current processor compatibility mode to the preferred mode that you specified.

When you migrate an active logical partition between servers with different processor types, both the current and preferred processor compatibility modes of the logical partition must be supported by the destination server. When you migrate an inactive logical partition between servers with different processor types, only the preferred mode of the logical partition must be supported by the destination server.

If you specify the default mode as the preferred mode for an inactive logical partition, you can migrate that inactive logical partition to a server of any processor type. Because all servers support the default processor compatibility mode, you can migrate an inactive logical partition with the preferred mode of default to a server with any processor type. When the inactive logical partition is activated on the destination server, the preferred mode remains set to default, and the hypervisor determines the current mode for the logical partition.