Overriding topology default assumptions

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6.18 LPAR mode z/VM guest KVM guest

Use the topology= kernel parameter to override default assumptions about the CPU topology.

By default, CPU topology support is enabled in the Linux® kernel. If no topology information is available, a topology is assumed where the CPUs share least resources, that is, each CPU is assumed to be on a different drawer.

Use the topology=off kernel parameter to override these defaults if they are not suitable for your workload.

Format

Figure 1. topology= syntax

1! topology=on
1 topology=off
off
Disables CPU topology support.
on
If no topology information is available, assumes that all CPUs are core siblings. If topology information is available, this setting is ignored.

Example

      topology=off

Dynamic changes

On a running Linux instance, you can read the current topology setting from /proc/sys/s390/topology. You can also write to /proc/sys/s390/topology to change the setting.

The value 1 corresponds to topology=on, and 0 corresponds to topology=off.

Example

# echo 0 > /proc/sys/s390/topology