How to improve TCP/IP performance for z/VSE running as a z/VM guest
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Today we got questions about z/VSE running in a z/VM guest. One aspect was TCP/IP performance in z/VM guests.
You may improve your network performance with the z/VM queue-I/O assist (QDIO performance assist) for z/VM V=V guests, if the guest uses real adapters and real networking devices via the Queued Direct I/O (QDIO) facility. z/VSE exploits queue-IO assist for OSA Express (CHPID type OSD) and HiperSockets (CHPID type IQD) devices.
With the aid of the assist, I/O interruptions can be passed directly from the hardware to the z/VM guest. In addition certain QDIO-related instructions can be interpretively executed by the processor without z/VM's involvement.
To exploit the queue-I/O assist function in z/VSE use the z/VM CP command "SET QIOASSIST ON" before you IPL the z/VSE system. After you enabled the queue-I/O assist function each z/VSE "DEFINE LINK,TYPE=OSAX" command will automatically exploit it.
The queue-I/O assist function is supported on z/VM 5.4 or higher. z/VM must be running in an LPAR and not as a z/VM guest.
The "z/VSE Planning" and "z/VM CP Commands and Utilities Reference" books provide more information.