User guide

3–InfiniBand
®
Cluster Setup and Administration
Performance Settings and Management Tips
3-38 IB0054606-02 A
 rpm (see “rpm” on page G-32)

strings (see “strings” on page G-32)
Adapter and Other Settings
The following adapter and other settings can be adjusted for better performance.
 Use an IB MTU of 4096 bytes instead of 2048 bytes, if available, with
the QLE7340, and QLE7342. 4K MTU is enabled in the ib_qib driver by
default. To change this setting for the driver, see “Changing the MTU Size”
on page 3-20.
 Make sure that write combining is enabled. The x86 Page Attribute Table
(PAT) mechanism that allocates Write Combining (WC) mappings for the
PIO buffers has been added and is now the default. If PAT is unavailable or
PAT initialization fails for some reason, the code will generate a message in
the log and fall back to the MTRR mechanism. See Appendix F Write
Combining for more information.
 Check the PCIe bus width. If slots have a smaller electrical width than
mechanical width, lower than expected performance may occur. Use this
command to check PCIe Bus width:
$ ipath_control -iv
This command also shows the link speed.
 Experiment with non-default CPU affinity while running
single-process-per-node latency or bandwidth benchmarks. Latency
may be slightly lower when using different CPUs (cores) from the default. On
some chipsets, bandwidth may be higher when run from a non-default CPU
or core. For the MPI being used, look at its documentation to see how to
force a benchmark to run with a different CPU affinity than the default. With
OFED micro benchmarks such as from the qperf or perftest suites, taskset
will work for setting CPU affinity.
NOTE
Run these tools to gather information before reporting problems and
requesting support.
NOTE
For the most current information on performance tuning refer to the QLogic
OFED+ Host Software Release Notes.