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Queued I/O Assist Requirements

The announcements for the z990 processor family and z/VM Version 4 Release 4.0 discussed performance improvements for V=V guests using real adapters and real networking devices that use the Queued Direct I/O (QDIO) facility.

The performance assist for V=V guests applies to the FICON Express card with FCP feature (FCP CHPID type), HiperSockets (IQD CHPID type), and OSA Express features (OSD CHPID type).

The performance improvements centered around replacing the heavyweight PCI interrupt interruption mechanism with a lighter adapter interrupt mechanism.

See the z990 page and the the z/VM 4.4.0 page for more information.

Recommended Service

To get best Queued I/O Assist performance from the System z processor and z/VM, it is necessary to ensure the systems and components involved are at appropriate service levels. Please consult the appropriate hardware and software service buckets. This web page documents key service that should be applied, but is not a substitute for the regular service research process.

IBM strongly recommends you apply these service levels before putting Queued I/O Assist technology into production in your environment.

Component Level Needed
z990 Ask your IBM CE to make sure your z990 is running current EC levels for MCL Driver 52G. In particular, EC J12558 needs to be at driver level 116 or later.
z/VM 4.4.0
Control Program 		Apply PTF UM31036 (APAR VM63385). While z/VM 4.4.0 is no longer in service, we leave this APAR reference since it was the PTF that enabled AIP and includes some information on the function.
z/VM 4.4.0
TCP/IP Feature 		Apply PTF UQ83180 (APAR PQ81580) and PTF UQ80870 (APAR PQ78679). While z/VM 4.4.0 is no longer in service, we leave this APAR reference since it was the PTF that enabled AIP and includes some information on the function.
z/VM 5.2.0 and 5.3.0
Control Program		 VM64287 Slow Ping Response Time over QDIO

A performance problem may occur when there is more than one virtual processor in a guest's configuration and the followi sequence of events take place:

  • LOGON a user with multiple virtual processors
  • IPL Linux or any QDIO capable Operating System
  • Establish and Activate a QDIO connection (doesn't matter whether it's OSA, HiperSockets or FCP) using AIs.
  • IPL Linux again (or issue a SYSTEM CLEAR CP Command)
  • Establish and Activate a QDIO connection again

Apply PTF UM32157 (z/VM 5.2.0) or PTF UM32158 (z/VM 5.3.0).

z/VM 5.3.0
Control Program		 VM64297 Paging Spike from Demand Scan Hangs System

Large spike in paging causes apparent hang situation. DEMAND SCAN effectively shuts down while paging tries to catch up.

Apply PTF UM32197 (z/VM 5.3.0)

z/VM 5.2.0 and 5.3.0
Control Program		 VM64306 Problems Running Linux on FCP SCSI Disk that are attached with QIOASSIST.

When running SLES10 SP1 or RHEL 5 under z/VM 5.3 or 5.2, with more than 2GB of guest storage defined and FCP or OSA devices attached with the Queued-I/O assist enabled (QIOASSIST), invalid data is read from and written to the affected FCP or OSA devices.

Apply PTF UM32194 (z/VM 5.2.0) or UM32198 (z/VM 5.3.0)

Linux for zSeries

You need QDIO code of the June 2003 stream dated 2003-10-31 or later.

If you need to upgrade your drivers, you can get appropriate driver levels from IBM DeveloperWorks. Download and install the "June 2003 stream", which contains the QDIO level needed.

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 Queued I/O Assist to see how things change.

  1. Log off any guests using assisted adapters. Even better, if at all possible, log off all guests using QDIO devices.

  2. From MAINT, issue this CP command: SET QIOASSIST OFF ALL

  3. Arrange for the networking adapters to be attached to the guests using the NOQIOASSIST option. You will have to do one of the following two things:
    • If the devices are DEDICATEd to the guest in the CP directory, put the NOQIOASSIST option on each DEDICATE statement. Remember to put the new CP directory online!
    • If the guest acquires the devices via the CP ATTACH command (in its own PROFILE EXEC, perhaps), change the ATTACH command to use the NOQIOASSIST option.

  4. Log on your guests and bring them up.

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 QIOASSIST. You should see that the assist is off.

  • Also from the guest console, issue this command: #CP QUERY VIRTUAL OSA. You should see that the adapters are running with QIOASSIST disabled.

Last revised Feb 8, 2008 (BKW)