AIX Version 4.3 Differences Guide

The nice value has a much greater impact on the priority of a thread. It is now
included in the calculation as a multiplier of the recent CPU usage in addition to
the use as a constant factor.
With the default values of 16 for sched_R and sched_D, and 60 for nice and
DEFAULT_NICE, the priority calculation equates to:
• Priority calculation: cpu / 2 + 60
• Once per second ageing of all threads: cpu = cpu / 2
Although the algorithm has changed, the default values provide an identical
function.
2.13.2 Sample Results of Altering Nice Value
The following tables list the results of changing the nice value of a thread on two
identical machines; one running the old algorithm, and the other running the new
algorithm. In each case, the tables list the percentage of CPU time delivered to
one thread that has been niced by the indicated delta, which is in competition with
varying numbers of default priority threads. All threads were running the same
CPU bound application.
From comparison of the values in Table 7 and Table 8, it can be seen that the
effect of a positive nice delta on a thread has been enhanced. Take, for example,
a thread running with a nice delta of 19 in competition with one default thread.
Previously, the niced thread would receive 41 percent of the CPU, with the default
thread receiving the remaining 59 percent. With the new algorithm, the niced
thread has been reduced to 15 percent, with the default thread increasing to 85
percent.
In addition, the effect of a negative nice delta has been increased. A thread
running with a nice delta of -20 competing against 31 default threads now
receives 32 percent of the CPU, compared with 23 percent under the previous
26 AIX Version 4.3 Differences Guide