pshpstuningguidewp040105.doc
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If you have eight cards for p690 (or four cards for p655), this command also indicates whether
you have full memory bandwidth.
3.8 Debug settings in the AIX 5L kernel
The AIX 5L kernel has several debug settings that affect the performance of an application. To
make sure you are running with all the debug settings in the kernel turned off, run the following
command:
bosdebug -L
The output will look something like this:
Memory debugger off
Memory sizes 0
Network memory sizes
0
Kernel debugger off
Real Time Kernel off
Check the output to make sure that all the debug settings are off. To change any of these settings,
run the following command:
bosdebug -o <variable>=off
After you make changes to the kernel settings, run the following command and then reboot:
bosboot -a
4.0 Daemon configuration
Several daemons on AIX 5L and the HPS can impact performance. These daemons run
periodically to monitor the system, but can interfere with performance of parallel applications. If
there are as many MPI tasks as CPUs, then when these demons run, they must temporarily take a
CPU away from a task. This perturbs the performance of the application if one task takes a little
longer to reach a synchronization point in its execution as compared to other tasks. Lowering the
frequency of these daemons can improve performance or repeatability of the performance of a
parallel application.
4.1 RSCT daemons
If you are using RSCT Peer Domain (such as VSD, GPFS, LAPI striping, or fail over), check the
IBM.ConfigRMd daemon and the hats_nim daemon. If you see these daemons taking cycles,
restart the daemons with
AIXTHREAD_SCOPE=S.
