Setting server parameters

Modified: 28 Apr 2022 01:26 UTC

The commands sdc-server get and sdc-server set can be used from the head node to manage server parameters. If no server UUID is specified, the command applies to the default setting. Otherwise, the command refers a server-specific over-ride of the default.

A compute node must be setup with sdc-server setup for the parameter to apply.

Currently, the only server parameter defined is smt_enabled, which controls whether simultaneous multi-threading is active on the server.

Controlling hyper-threading

Simultaneous multi-threading (SMT), also known as hyper-threading on Intel systems, is a CPU feature that provides more CPUs by sharing some hardware resources.

By default, Triton systems will have simultaneous multi-threading enabled at the OS level. The current state for a particular node can be observed via the Operations Portal, or by examining the smt_enabled value in sdc-server sysinfo. If the value is missing, the node is probably running an older platform image, and SMT will be enabled.

You may prefer to disable SMT on systems where untrusted tenants will run, or for other security reasons. On a system where SMT has been disabled in software like this, the number of CPUs reported as 'on-line' will be less than the total count. SMT sibling CPUs are reported in tools such as psrinfo as disabled.

You can do this with sdc-server set smt_enabled=false. This sets the default: after setting this, any new compute nodes added to the data center will boot with SMT disabled. Any existing compute nodes will continue to operate with their existing setting.

You can also over-ride this on a per-system setting by specifying a UUID. For example:

[root@headnode (emy-15) ~]# sdc-server lookup headnode=true
[root@headnode (emy-15) ~]# sdc-server set 44454c4c-4800-104c-8035-c6c04f544432 smt_enabled false

As the example shows, this can apply to the head node as well as compute nodes.

A reboot of the system in question is required to actually change the effective setting.