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Tuning Kernel Settings for AIX

There are a number of AIX kernel settings you can tune for optimal Siebel Server or Web server performance under AIX. These include the Virtual Memory Management and TCP settings. You must have root privileges to modify these settings. (On AIX 5.2, kernel settings can alternatively be tuned using vmo rather than vmtune.)

To change the kernel settings using vmtune

  1. Using a text editor such as vi, open the /etc/ file for editing.
  2. Modify the vmtune settings, as follows:

    if [ -f /usr/samples/kernel/vmtune ] ; then

    /usr/samples/kernel/vmtune -p 5 -P 8 -f 720 -F 768 -b 200 -s 1

    In providing values for minfree (-f for vmtune) and maxfree (-F for vmtune), use the following formulas:

    • minfree = number_of_CPUs * 120 = 6 * 120 = 720
    • maxfree = number_of_CPUs * (120 + maxpgahead) = 6 * (120 + 8) = 768


      number_of_CPUs = the number of CPUs on the AIX server you are tuning (for example, 6)

      maxpgahead = the value of the maxpgahead (-R for vmtune) parameter: for example, 8)

  3. Modify the network options, as follows:

    if [ -f /usr/sbin/no ] ; then

    /usr/sbin/no -a rfc1323=1

    /usr/sbin/no -a tcp_sendspace=131072

    /usr/sbin/no -a tcp_recvspace=131072

    /usr/sbin/no -a rfc2414=1

    /usr/sbin/no -a tcp_init_window=3

    /usr/sbin/no -a use_isno=0

    /usr/sbin/no -a tcp_nagle_limit=0

  4. Check the settings for all User Limits (ulimit) and make sure that they are set to -1 (unlimited), as follows:

    ulimit -a

    NOTE:  To change the set limits, update the /etc/security/limits file by changing all ulimit parameter values to -1 (unlimited).

  5. Save your changes and exit the editor.
  6. Restart the server machine to have the new settings take effect.
Performance Tuning Guide