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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.

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IBM pSeries User Manual Page 18