In this and the next several blog entries I will explain SUSE YES Certification testing under the covers: specific tests in SUSE YES Certification which are not fully documented on the certification bulletin. This discussion covers the power management features in SUSE Linux Enterprise that are tested on hardware during certification. Through YES Certification the SUSE Linux power management capabilities are validated on certified servers or workstations (including desktops, laptops and netbooks). If power management works correctly on your systems, then your systems are more power-efficient and save your company money.
The first two power management functionality tests are Hibernate (a.k.a. ACPI S4 or Suspend to Disk) and Sleep (a.k.a. ACPI S3 or Suspend to RAM). These are both optional tests on servers but always required on workstations and laptops. (There is an ongoing community debate whether Hibernate or Sleep makes sense on servers; some think so others do not. I will not get into that debate here). If the hardware manufacturer decides to support Hibernate or Sleep on their server hardware, then the YES Certification bulletin will include a configuration note highlighting this support. If no note is included on the server bulletin, then they are not supported on that system. On a workstation certification bulletin a configuration note is only required for Hibernate and Sleep if the hardware failed the testing and is not fully compatible with SUSE Linux Enterprise. Hibernate saves a system configuration (including the running processes) on the hard drive and then completely powers the system off. Sleep saves the system configuration to RAM, stopping many of the power-consuming components, but the RAM must remain powered. The system must be restored to a fully functioning state, essentially by reversing the hibernation or suspend process, to pass the certification test. The restore process is where many systems fail in their compatibility with SUSE.
The next power management component tested is CPU Frequency Scaling. This is an extremely important feature for your systems to be compatible with if you want to save power, whether your systems are high-end servers in a data center or a laptop on a long flight. Most modern processors have load-based frequency changing capability built-in. SUSE Linux Enterprise uses this functionality to increase or decrease the processor frequency based on system workload. The frequency is the speed or gigahertz (GHz) that each processor runs at while in operation. For example, a processor that is designed to operate at 3.40 GHz could be scaled back to 1.20 GHz if the system is not doing much. The lower the operating frequency the less power the processor and overall system use. Imagine how much less efficient your car gas mileage would be if you kept the engine revved up whenever you were stopped. The processor is one of the main power-consuming components in a system. So, if a system does not need the higher computational power because of its workload, SUSE Linux Enterprise will reduce the frequency and save you power costs. The instant the workload increases, your processors increase speed to handle the load. There are two main causes of CPU frequency scaling failure: 1) the processor supports it but the hardware manufacturer has not implemented it in the system firmware; 2) the system firmware or processor microcode implementation causes erratic or inconsistent CPU speed fluctuation.
Next I will quickly bullet a few power management tests that are certified only on SUSE Linux Enterprise Desktop systems. The first two are run on workstations and laptops; the final three are only run on laptops.
- Throttling test. This tests a feature in the processor that slows down the number of instructions handled over a given time period; it is a predecessor to CPU frequency scaling. Essentially, the processor delays its work for longer than is typical, which cuts down the amount of power used.
- Fan thermal test. Systems have a number of devices that monitor temperature and help keep the system from overheating. The fans are one example of this type of device, but even processors have thermal capabilities that fall into this category by performing temperature monitoring.
- Brightness test. Most laptops have function keys on the keyboard to brighten or dim the screen. These need to function with the operating system to provide power savings.
- Lid close test. When you close the lid on a laptop, does the system go into sleep, hibernate or some other power saving mode? If not, it should.
- Battery test. The operating system needs to be aware that a system is running on battery power and function accordingly to save power, and when the system is plugged back in, the operating system needs to monitor the battery recharging process.
Most of the above power management tests validate whether a system has implemented the ACPI (Advanced Configuration and Power Interface) standard fully or correctly. YES Certification verifies these power management functions between the hardware and the operating system.I hope this gives you a better appreciation for the information that exists when you use YES Certification to help you buy SUSE-compatible hardware. You can find more information about SUSE YES Certification at https://www.suse.com/partners/ihv/yes/. Stay tuned for future blog topics about SUSE YES Certification testing under the covers.