0: Two years ago, when a colleague had root access to our
1: lab's SUN 4500s (8 processors each, each running at 500mhz),
2: we decided that all those spare processor cycles were
3: going to waste.  With his knowledge of UNIX calls and
4: my affinity for perl, we came up with a SETI runner which
5: fired up new instances when the system was idle, and
6: killed instances when the system load went up.
7: <readmore>
8: 
9: my $uptime       = "uptime";  # or whatever it's called...
10: 
11: my $setiRoot     = '/usr/bin/seti';
12: my $setiBinary   = 'setiathome';
13: my $setiFlags    = '';
14: my $setiLog      = 'seti.log';
15: 
16: my $napTime      = 2;
17: 
18: my $maxInstances = 8;    # maximum number of SETI instances
19: my $minInstances = 0;    # minimum number of SETI instances
20: my $lowThreshold = 8.00; # start SETI
21: my $hiThreshold  = 9.00; # stop SETI
22: 
23: my @setiPids;            # pid array
24: 
25: while(1)
26: {
27:    sleep( $napTime );
28:    
29:    my $uptime = `$uptime`;
30:    
31:    $uptime = $1 if $uptime =~ /load average: (\d+\.\d\d)/;
32: 
33:    print STDERR "load average: $uptime\n";
34:    
35:    #
36:    # if the uptime is below a certain load,
37:    # then fire up a new SETI instance.
38:    #
39:    &startSETI
40:       if ( ($uptime < $lowThreshold) && (@seti < $maxInstances) );
41:    
42:    #
43:    # if the uptime is above a certain load,
44:    # then kill a SETI instance.
45:    #
46:    &stopSETI
47:       if ( ($uptime > $hiThreshold) && (@seti > $minInstances) );
48: }
49: 
50: #
51: # Organize our list of PIDs
52: #
53: sub startSETI
54: {
55:    print STDERR "Firing up a SETI...\n";
56:    print STDERR "We have ", scalar( @setiPids ), " PIDs:\n";
57:    print STDERR join( " ", @setiPids ), "\n";
58:    # list all processes
59:    my $number = scalar( @setiPids );
60:       
61:    chdir( "$setiRoot/seti$number" );
62:    
63:    print STDERR "Working directory: $setiRoot/seti$number\n";
64:    
65:    push( @setiPids, `$setiBinary $setiFlags > $setiLog` );
66: }
67: 
68: #
69: # Quick and dirty killer
70: #
71: sub stopSETI
72: {
73:    print STDERR "Shutting down a SETI...\n";
74:    
75:    kill 9, pop @setiPids;
76: }