Monday, February 14, 2011
The Satellite has several types of monitors that observe the behavior of a device in real time during testing. This week we will look at the Linux System Monitor, which is used to observe system performance. By watching this monitor, you can examine resource usage and task count to determine the extent to which device performance is affected under normal and abnormal operating conditions. Of course it is expected that performance will be affected during testing, but you might discover that it is affected more extremely than you had anticipated.
The Linux System Monitor is required for Achilles Level 1 Certification for host-based devices (HBD) running Linux. If you are using the Satellite to determine whether such an HBD would pass certification, it is necessary to configure and enable this monitor. ISA99 defines an HBD as a general purpose device running a general-purpose operating system capable of hosting one or more applications or data stores. An example is a human-machine interface (HMI), an engineering workstation, a historian server, or a domain controller.
How Does the Monitor Work?
The Linux System Monitor makes an SSH connection to the device to receive system performance information every second. This information includes CPU utilization, memory utilization (excluding the buffer and cache), and the number of tasks that are running on the device. The monitor watches for configured thresholds for maximum CPU usage, maximum memory usage, and minimum task count, and reports if any of these thresholds is crossed during testing. The thresholds are configurable so that they are meaningful for the tested device. For example, you could configure the maximum CPU usage threshold to be 100% as this value often indicates that there is a problem with a device. when configuring the monitor, you should observe the real-time data displayed in the Satellite's UI during normal operation of the device to determine the starting values for memory usage and task count.
What are the Linux System Monitor Requirements for Certification?
During HBD Certification, the tested device's CPU usage must not reach 100%, the memory must not exceed 125% of the starting memory usage, and the task count must not fall below the starting task count (the number of tasks active on the system during normal operation). If any of these conditions occur, the CPU usage, memory usage, and task count must return to the acceptable level within a specified period of time.
Where can you find additional information about HBD Certification?
Click here for further information about Level 1 HBD Certification.