QDIO Enhanced Buffer State Management Requirements

The QDIO Enhanced Buffer State Management facility (QEBSM) provides virtual machines running under z/VM an optimized mechanism for transferring data via QDIO (including FCP, which uses QDIO).

Recommended Service

The following service is recommended in order to use QEBSM. No service is required to enable QEBSM on z/VM 5.2.0.

Component Level Needed
z890, z990, z9 Ask your IBM CE to make sure you are running with EC J13484 driver level 137 or later for z890/z990 or EC J99673 driver level 83 or later for z9.
z/VM 5.2.0
Control Program 		Apply PTF UM31710 (APAR VM63838).

When running QEBSM in a virtual machine the following problems may be encountered depending on the timing of different events within the system:

  1. IPLing Linux from a SCSI device on a dedicated FCP subchannel may hang during the IPL process
  2. Specifying NOQIOASSIST on the ATTACH CP Command or the DEDICATE directory statement may cause the input queue for a QDIO subchannel to stall. This will cause all active communications to cease for a FCP, OSA or HiperSockets device.
  3. Running intense FCP, OSA or HiperSockets workloads may encounter either a HTT001 or LCKxxx ABEND when the device is simultaneously being DETACHed or the QDIO
Linux for zSeries

You need Linux with QEBSM enabled. This requires Linux 2.6.16 or later. For more details refer to the "October 2005 stream" on IBM DeveloperWorks.

How to Disable It

If you are experiencing performance problems with the FICON Express card with FCP feature (FCP CHPID type), HiperSockets (IQD CHPID type), or OSA Express features (OSD CHPID type), you might consider disabling QEBSM to see how things change.

  1. Detach the FCP, OSA or HiperSockets devices from your virtual machine

  2. Attach the devices back to your virtual machine with the NOQIOASSIST option or specify NOQIOASSIST on the DEDICATE statement for the device in the user's directory entry.

  3. IPL your virtual machine.

To confirm that your guest is running with the assist disabled, do this:

  • From the virtual console of your guest, issue this command: #CP QUERY V. You should see that the QEBSM does not appear in the output and QIOAssist DISABLED is displayed.

Last revised Jan. 03, 2007 (CCB)