#! perl -slw
use strict;
use Win32::API::Prototype;

ApiLink(
    'kernel32', q[
        BOOL GetSystemTimes(
            LPFILETIME lpIdleTime,
            LPFILETIME lpKernelTime,
            LPFILETIME lpUserTime
        )
    ]
) or die $^E;

sub SystemTimes {
    my( $idleTicks, $kernelTicks, $userTicks ) =( chr( 0 ) x 8 ) x 3;
    GetSystemTimes( $idleTicks, $kernelTicks, $userTicks ) or die  $^E;

    return map{
        my( $lo, $hi ) = unpack 'VV', $_;
        ( $hi * 2**32 + $lo );
    } $idleTicks, $kernelTicks, $userTicks;
}

use constant { IDLE=>0, KERNEL=>1, USER=>2 };
$|=1;

my @last = SystemTimes;


while( sleep 1 ) {
    my @now = SystemTimes;
    my @deltas = map{ $now[ $_ ] - $last[ $_ ] } IDLE, KERNEL, USER;
    my $busy = $deltas[ KERNEL ] + $deltas[ USER ];
    my $pcUsage = ( $busy - $deltas[ IDLE ] )* 100 /( $deltas[ IDLE ] || 100e5 );
    printf "\rCPU usage(%%): %6.3f ", $pcUsage;
    @last = @now;
}

__END__
C:\test>SysTimes.pl
CPU usage(%): 25.490