Power consumption is a priority for NETINT customers and a passion for NETINT engineers and technicians. Matthew Ariho, a system engineer in SoC Engineering at NETINT, recently answered some questions about:
How to test power consumption
Which computer components draw the most power
Why using older computers is bad for your power bills, and
The best way for video-centric data centers to reduce power consumption.
What are the different ways to test power consumption (and cost)?
There are software and hardware-based solutions to this problem. I use one of each as a means of confirming any results.
One software tool is the IPMItool linux package which provides a simple command-line interface to IPMI-enabled devices through a Linux kernel driver. This tool polls the instantaneous, average and peak and minimum instantaneous power draw of the over a sampling period.
On the hardware side of things, you can use different forms of multimeters, like the Kill-A-Watt meter and a 208VAC power bar are examples of such devices available in our lab.
What are their pros and cons (and accuracy)?
The IPMItool is great because it provides a lot of information. It is fairly simple to set up and use. There is a question of reliability because it is software based, it depends on readings whose source I’m not familiar with.
The multimeters (like the Kill-A-Watt meter), while also simple to use, do not have any logging capabilities which makes measurements like average or steady state power draw difficult to measure. Both methods have a resolution of 1W which is not ideal but more than sufficient for our use cases.
What activities to you run when you test power consumption?
We run multi-instances that mimic streaming workloads but only to the point that each of those instances is performing up to par with our standards (for example, 30 fps).
What’s the range of power consumption you’ve seen?
I’ve seen reports of power consumption of up to 450 watts, but personally never tested a unit that drew that much. Typically, without any load on the T408 devices, the power consumption hovers around 150W, which increases to 210 to 220W during peak periods.
What’s the difference between Power Supply rating and actual power consumption (and are they related)?
Power supplies take in 120VAC or 208VAC and convert to various DC voltages (12V, 5V, 3.3V) to power different devices in a computer. This conversion process inherently has several inefficiencies. The extent of these inefficiencies depends on the make of the power supply and the quality of components used.
Power supplies are offered with an efficiency rating that certify how efficiently a power supply will function at different loads. Power consumption measured at the wall will always be less than power supplied within a computer.
What are the hidden sources of excessive power that most people don’t know about?
The operating system of a computer can consume a lot of power performing background tasks though this has become less of a problem with more efficient CPUs on the market. Other sources of excessive power are bloatware that are usually unnecessary programs that run in the background.
What distinguishes a power-hungry computer from an efficient one – what should the reader look for?
The power supply rating is something to watch. Small variations in the power supply rating make significant differences in efficiency. The difference between a PSU rated at 80 PLUS and a PSU rated at 80 PLUS Bronze is about 2% to 5% depending on the load. This number only grows with better rated PSUs.
Other factors including the components of the computer. Recently, newer devices (CPUs, GPUs and motherboards) have been made with beyond significant generational improvements in efficiency. A top-of-the-line computer from 3 years ago simply cannot compete with some mid-range computers in terms of both power efficiency or performance. So, while sourcing older but cheaper components in the past may have been a good decision, nowadays, its not as clear cut.
Which components draw the most power?
CPUs and GPUs. Even consumer CPUs can draw over 200W sustained. GPUs on the lower end consume around 150W and now more recently over 400W.
How does the number of cores in a computer impact power usage?
I’m really not an expert on server components and it is hard to say without having examples. There are too many options to provide a conclusion on a proper trend. There are AMD 64 core server CPUs that pull about 250 to 270 W and 12 to 38 core Intel server CPUs that do about the same. Ultimately architectural advantages/features determine performance and efficiencies when comparing CPUs across manufacturer or even CPUs from the same manufacturer.
One famous quote attributed to Peter Drucker is that you can’t manage what you don’t measure. As power consumption becomes increasingly important, it’s incumbent upon all of us to both measure and manage it.