There's no way you can set CPU usage to a percentage of CPU time. Anyway, you don't want to do that, because it would mean that your CPU would idle some of the time while at other times it still cannot perform the other (more important) tasks. What you want is for your script to use the CPU 100% when no other task is waiting to be run, but to release the processor when another process needs it.

The way this is done in *NIX is the process priority (otherwise known as the "nice" value). This is a value between -20 (highest priority, process is prioritized over all other processes) and 19 (lowest priority). Process priority can be set either on the commandline vie the "nice" or "renice" commands, e.g.

nice -n 10 perlscript.pl
# or, if the process is already running
renice 10 -p <PID>
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(see the man pages for these commands for more details). Or with the BSD::Resource module method setpriority

use BSD::Resource;
my $success = setpriority(0,10);
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#!/usr/bin/perl
#Description:  These subs allow you control how much % CPU maximum wil
+l use your script. CPU_start() must be called once when you script st
+art.
#This example script will use 30% CPU until Ctrl-C pressed:

CPU_start(); CPU_max(30) while 1;

use Time::HiRes qw(time);

sub CPU_used {
(map {$_->[13]+$_->[14]}
[split " ", Cat("/proc/self/stat")])[0]
}

{ my %start = (tm => 0, cpu => 0);
sub CPU_start { @start{"tm","cpu"} = (time(),CPU_used()) }
sub CPU_max {
my ($max, $real, $cpu) = ($_[0], time()-$start{tm},
CPU_used()-$start{cpu});
return unless defined($max) and $max > 0;
&sleep( $cpu/$max-$real );
}}

#
# macro used from CPU_used() and CPU_max()
#

sub sleep { select undef,undef,undef,$_[0] }
sub Cat {
local *F;
open F, "< ".$_[0] or return;
local $/ unless wantarray;
return <F>;
}
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