Managing the workload

If a system is sufficiently well tuned for its applications and uses to which it is normally put, you still have a number of options open to you if you are looking for further performance gains. This involves managing the system's workload with the cooperation of the system's users. If they can be persuaded to take some responsibility with you (as the system administrator) for the system's performance, then significant improvements can usually be made. Below are some steps that users and administrators can take to alleviate excessive demands on a system without reconfiguring the kernel.

• Move jobs that do not have to run at a particular time of day to off-peak hours. Encourage users to submit jobs using at(C), batch(C), or crontab(C) depending on whether they are one-off (at or batch) or periodic jobs (crontab).

• Collect data on the average system workload and publish it to users so that they are aware of the daily peaks and troughs. If they have the flexibility to choose when to run a program, they will know when they can achieve more work.
  

• Adjust the default nice value of user processes using the Hardware/Kernel Manager. This will set a lower CPU priority for all user processes, and will allow critical jobs with higher priority to use the CPU more frequently.

• Encourage users to reduce the priority of their own processes using nice(C) and renice(C); this is especially important for those jobs that do not perform much I/O activity -- these CPU-intensive jobs are likely to monopolize the available processing time.

• The default action of the Korn shell ( ksh(C)) is to run background jobs at a reduced priority. Make sure users have not altered this setting in their .profile or .kshrc files.

• Encourage users to kill unnecessary processes, and to log out when they have finished rather than locking their screen.

• Reduce the maximum number of processes that a user can run concurrently by lowering the value of the kernel parameter MAXUP. For example, MAXUP set to 20 means that a user can run 19 other processes in addition to their login shell.