smtctl Command

Purpose

The smtctl command controls the enabling and disabling of processor simultaneous multithreading mode.

Syntax

smtctl [ -m off | on [ -w boot | now ]]

smtctl [-t #SMT [-w boot | now ]]

Description

This command is provided for privileged users and applications to control utilization of processors with simultaneous multithreading support. The simultaneous multithreading mode allows processors to have thread level parallelism at the instruction level. This mode can be enabled or disabled for all processors either immediately or on subsequent boots of the system. This command controls the simultaneous multithreading options.

Flags

Item	Description
-m off	Set the simultaneous multithreading mode to `disabled`. This option cannot be used with the -t flag.
-m on	Set the simultaneous multithreading mode to `enabled`. By using the -m flag, the maximum number of threads supported per processor is enabled. This option cannot be used with the -t flag.
-t #SMT	Set the number of the simultaneous threads per processor. The value may be set to one to disable simultaneous multi-threading. The value may be set to two for systems that support 2-way simultaneous multi-threading and the value may be set to four, for the systems that support 4-way simultaneous multi-threading. This option cannot be used with the -m flag.
-w boot	Makes the simultaneous multithreading mode change effective on next and subsequent reboots if you run the bosboot command before the next system reboot.
-w now	Makes the simultaneous multithreading mode change immediately but will not persist across reboot. If neither the -w boot or the -w now options are specified, then the mode change is made immediately. It will persist across subsequent reboots if you run the bosboot command before the next system reboot.
-m limit	Limits the number of simultaneous multithreading threads to two, and enables more processor nodes, if available, effective at the next reboot (running bosboot is required to rebuild the boot image). This limit cannot be dynamically changed during run time, and you must reboot to change the operating state.
-m suspend	Suspends the simultaneous multithreading capability, and enables more processor nodes, if available, effective at the next reboot (running bosboot is required to rebuild the boot image). This limit cannot be dynamically changed during run time, and you must reboot to change the operating state.

If no options are specified then the following simultaneous multithreading settings will be reported:

Item	Description
SMT Capability	Indicator that the physical or virtual processors are capable of simultaneous multithreading.
SMT Mode	Current runtime simultaneous multithreading mode of `disabled` or `enabled`.
SMT Boot Mode	Current boot time simultaneous multithreading mode of `disabled` or `enabled`.
SMT Threads	Number of simultaneous multithreading threads per physical or virtual processor.
SMT Bound	Indicator that the simultaneous multithreading threads are bound on the same physical or virtual processor.
SMT Thread Capability	Maximum number of simultaneous multi-threading threads per physical or virtual processor supported by the system.

Exit Status

Item	Description
0	Successfully completed the requested operation.
>0	An error occurred.

Security

Attention RBAC users and Trusted AIX users: This command can perform privileged operations. Only privileged users can run privileged operations. For more information about authorizations and privileges, see Privileged Command Database in AIX® Version 7.1 Security. For a list of privileges and the authorizations associated with this command, see the lssecattr command or the getcmdattr subcommand.

Examples

To enable simultaneous multithreading for the current boot cycle, enter:
```
smtctl -m on -w now
```
The system displays a message similar to the following:
```
smtctl: SMT is now enabled.
```
To enable a 2-way simultaneous multithreading on a system that supports up to 4 way, enter:
```
smtctl -t 2 -w now
```
The system displays a message similar to the following:
```
smtctl: SMT is now enabled.
```

To view the current simultaneous multithreading mode settings and processor information, enter:

smtctl

The system displays a message similar to the following:

This system is SMT capable.

This system supports up to 4 SMT threads per processor
SMT is currently enabled.

SMT boot mode is set to disabled.


proc0 has 2 SMT threads
Bind processor 0 is bound with proc0
Bind processor 1 is bound with proc0


proc2 has 2 SMT threads
Bind processor 2 is bound with proc2
Bind processor 3 is bound with proc2

To disable simultaneous multithreading for the current boot cycle and for all subsequent boots, enter:
```
smtctl -m off
```
The system displays a message similar to the following:
```
smtctl: SMT is now disabled. It will persist across reboots if
        you run the bosboot command before the next reboot.
```
Another method to disable simultaneous multi-threading for the current boot cycle and for subsequent boots, enter:
```
smtctl -t 1
```
Note: The boot image must be remade with the bosboot command before the next reboot.

Location

/usr/sbin/smtctl

Files

Item	Description
/usr/sbin/smtctl	Contains the smtctl command.