AIX 5L Problem Determination - IBM Redbooks

Priority calculation parameters
The priority of most user processes varies with the amount of CPU time the
process has used recently. The CPU scheduler’s priority calculations are based
on two flags that are set with schedtune, -r and -d. The formula used by the
scheduler to calculate the amount to be added to a process’s priority value as a
penalty for recent CPU use is:
CPU penalty = (recently used CPU value of the process) * (r/32)
The once-per-second recalculation of the recently used CPU value of each
process is:
new recently used CPU value = (old recently used CPU value of the process) *
(d/32)
Both -r and -d have default values of 16. This maintains the CPU scheduling
behavior of previous versions of the operating system.
Memory load control parameters
The operating system scheduler performs memory load control by suspending
when memory is over committed. Memory is considered over committed when
the following condition is met:
p * h s
Where p is the number of pages written to paging space in the last second, h is
an integer specified by the -h flag, and s is the number of page steals that have
occurred in the last second.
A process is suspended when memory is over committed and the following
condition is met:
r * p f
Where r is the number of repages that the process has accumulated in the last
second, p is an integer specified by the -p flag, and f is the number of page faults
that the process has experienced in the last second.
Time slice increment parameter
The schedtune command can also be used to change the amount the operating
system allows a given process to run before the dispatcher is called to choose
another process to run (time slice). The default value for this interval is a single
clock tick (10 milliseconds). The -t flag of the schedtune command allows the
user to specify the number of clock ticks by which the time length is to be
increased.
Chapter 10. Performance problem determination 255