You need to set "Log Level" for both server and vhost to "DEBUG".
Now i get this:
2007-04-10 00:14:20.882 DEBUG Failed to execute 'mpstat' command: No such file or directory
2007-04-10 00:14:25.886 DEBUG Failed to execute 'mpstat' command: No such file or directory
2007-04-10 00:14:30.890 DEBUG Failed to execute 'mpstat' command: No such file or directory
2007-04-10 00:14:35.894 DEBUG Failed to execute 'mpstat' command: No such file or directory
2007-04-10 00:14:40.898 DEBUG Failed to execute 'mpstat' command: No such file or directory
2007-04-10 00:14:45.903 DEBUG Failed to execute 'mpstat' command: No such file or directory
2007-04-10 00:14:50.907 DEBUG Failed to execute 'mpstat' command: No such file or directory
2007-04-10 00:14:55.911 DEBUG Failed to execute 'mpstat' command: No such file or directory
2007-04-10 00:15:00.915 DEBUG Failed to execute 'mpstat' command: No such file or directory
2007-04-10 00:15:05.920 DEBUG Failed to execute 'mpstat' command: No such file or directory