z/VM: CP Commands and Utilities Reference - z/VM - IBM

SET QIOASSIST
►►
SET
Notes:
Authorization
Purpose
Operands
QIOAssist
ON
OFF
1 Class B users only.
2 Class B users only.
FOR
Privilege Class: B, G
*
(1)
ALL
USER
(2)
userid
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:
v The processor must support the queue-I/O assist. See the General Information
Manual.
v z/VM must be running in a logical partition and not as a guest.
v The assist must be globally enabled with the CP SET QIOAssist ON ALL
command.
v The virtual machine must be enabled with the CP SET QIOAssist ON command.
v The device must not be attached to the virtual machine with the NOQIOAssist
option of the CP ATTACH command or the system-directory DEDICATE
statement.
v The virtual machine must not be using the CP TRACE command.
SET QIOASSIST
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
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Chapter 2. CP Commands 1329