Q-Logic IB0056101-00 G.02, OFED manual Use the ipathmtrr Script to Fix Mtrr Issues

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Write Combining MTRR Mapping and Write Combining

For systems with very large amounts of memory (32GB or more), it may also be necessary to adjust the BIOS setting for the PCI hole granularity to 2GB. This setting allows the memory to be mapped with fewer MTRRs, so that there will be one or more unused MTRRs for the InfiniPath driver.

Some BIOS’ do not have the MTRR mapping option. It may have a different name, depending on the chipset, vendor, BIOS, or other factors. For example, it is sometimes referred to as 32 bit memory hole. This setting must be enabled.

If there is no setting for MTRR mapping or 32 bit memory hole, and you have problems with degraded performance, contact your system or motherboard vendor and ask how to enable write combining.

Use the ipath_mtrr Script to Fix MTRR Issues

QLogic also provides a script, ipath mtrr, which sets the MTRR registers, enabling maximum performance from the InfiniPath driver. This Python script is available as a part of the InfiniPath software download, and is contained in the infinipath* RPM. It is installed in /bin.

To diagnose the machine, run it with no arguments (as root):

#ipath mtrr

The test results will list any problems, if they exist, and provide suggestions on what to do.

To fix the MTRR registers, use:

#ipath mtrr -w

Restart the driver after fixing the registers.

This script needs to be run after each system reboot. It can be set to run automatically upon restart by adding this line in /etc/sysconfig/infinipath:

IPATH_MTRR ACTIVE=1

See the ipath mtrr(8) man page for more information on other options.

IB0056101-00 G.02 Preliminary B-3