User guide

F–Write Combining
Verify Write Combining is Working
IB0054606-02 A F-3
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.
Verify Write Combining is Working
To see if write combining is working correctly and to check the bandwidth, run the
following command:
$ ipath_pkt_test -B
With write combining enabled, the QLE7140 and QLE7240 report in the range
of 1150–1500 MBps. The QLE7280 reports in the range of 1950–3000 MBps.
You can also use ipath_checkout (use option 5) to check bandwidth.
Increased latency and low bandwidth may indicate a problem. The interconnect
could be operating in a degraded performance mode with latency increasing to
several microseconds, and bandwidth decreasing to as little as 200 MBps.
Upon driver startup, you may see these errors:
ib_qib 0000:04:01.0: infinqib0: Performance problem: bandwidth
to PIO buffers is only 273 MiB/sec
.
.
.
If you do not see any of these messages on your console, but suspect this
problem, check the /var/log/messages file. Some systems suppress driver
load messages but still output them to the log file.