SET QIOASSIST
Authorization
Privilege Class: B, G
Purpose
Use SET QIOASSIST to control the queue-I/O assist (QDIO performance assist for V=V guests) for a virtual machine. This interpretive-execution assist applies to devices that use the Queued Direct I/O (QDIO) architecture, HiperSockets devices, and FCP devices.
On processors that support the queue-I/O assist, there is a performance benefit for I/O performed with the queued-I/O protocols. With the aid of the assist, I/O interruptions can be passed directly from the hardware to the virtual machine. In addition, certain QDIO-related instructions can be interpretively executed by the processor, without z/VM®'s involvement.
To use queue-I/O assist, the following are required:
- The processor must support the queue-I/O assist. See z/VM: General Information.
- z/VM must be running in a logical partition and not as a guest.
- The assist must be globally enabled with the CP SET QIOASSIST ON ALL command.
- The virtual machine must be enabled with the CP SET QIOASSIST ON command.
- The device must not be attached to the virtual machine with the NOQIOASSIST option of the CP ATTACH command or the system DEDICATE directory statement.
- The virtual machine must not be using the CP TRACE command.
Operands
- ON
- OFF
- turns the queue-I/O assist on or off for a virtual machine.
- ALL
- enables or disables eligibility for all virtual machines to use the queue-I/O assist, independent of the individual settings for each user. The individual settings are not changed. When ALL is specified by a class B user, access to the queue-I/O assist is allowed or disallowed for all virtual machines, including any new users that might log on. When this global setting is OFF, it overrides any individual user's setting to allow the assist.
- USER userid
- specifies an individual user of the queue-I/O assist.
- *
- specifies the queue-I/O assist setting is for the command issuer's virtual machine.
Usage Notes
- If QIOASSIST is set ON for all users, an individual user can set QIOASSIST OFF without changing
the setting for other users. Note: The reverse is not true; setting OFF for ALL overrides individual user settings.
- Setting QIOASSIST ON or OFF for ALL users may not immediately enable or disable the assist for all users. The command will take effect as soon as possible. Use the QUERY QIOASSIST to determine when the user's virtual machine is in the desired state.
- If z/VM is not running on a configuration that supports the queue-I/O assist, the SET QIOASSIST command is not supported and an error message is issued.
Examples
The following command will disable userid test1 from using the queue-I/O assist.
set qioassist off test1
Messages
- HCP002E Invalid operand - operand
- HCP026E Operand missing or invalid
- HCP045E userid not logged on
- HCP263E Too many operands were supplied for this command
- HCP1014E A required option is missing
- HCP2162I QIOAssist is not available