IBM pSeries - Manual (Page 18)

pshpstuningguidewp040105.doc Page 18
SCHEDD_DEBUG = -D_ALWAYS
4.3 Settings for AIX 5L threads
Several variables help you use AIX 5L threads to tune performance. These are the recommended
initial settings for AIX 5L threads when using HPS. Set them in the /etc/environment file.
AIXTHREAD_SCOPE=S
AIXTHREAD_MNRATIO=1:1
AIXTHREAD_COND_DEBUG=OFF
AIXTHREAD_GUARDPAGES=4
AIXTHREAD_MUTEX_DEBUG=OFF
AIXTHREAD_RWLOCK_DEBUG=OFF
To see the current settings on a running system, run the following command:
ps ewaux | grep -v grep | grep -v AIXTHREAD_SCOPE
4.4 AIX 5L mail, spool, and sync daemons
AIX 5L automatically starts daemons for print spooling and mail. Because these are usually not
needed on HPS systems, they can be turned off. To dynamically turn off these daemons on a
running system, use the following commands:
stopsrc -s sendmail
stopsrc -s qdeamon
stopsrc -s writesrv
You can also change the frequency when the syncd daemon for the file system runs.
In the /sbin/rc.boot file, change the number of seconds setting between syncd calls by increasing
the default value of
60 to something higher. Here is an example:
nohup /usr/sbin/syncd 300 > /dev/null 2>&1 &
You also need to change the sync_release_ilock value to
1 by using the following command:
ioo -p -o sync_release_ilock=1
4.5 Placement of POE managers and LoadLeveler scheduler
Select one node to run POE managers for MPI jobs and to run the LoadLeveler scheduler. If
possible, do not use a compute node. If you do use a compute node, make sure that the CPUs on
it do not all try to run an MPI task. Otherwise, tasks assigned to that node will run slightly slower
than tasks on other compute nodes. A single slow task in a parallel job is likely to slow the entire
job.