To further understand the reason behind this, we charted the way CPU technology (lithography) has evolved over time, along with performance and idle power consumption (see Figure 2).

Note: The color-coded vertical bars represent generations — lithography — of processor technology (usually, Intel). For each generation of around three to four years, hundreds of servers are released. The steeper the rise of the orange line (compute performance per watt), the better. For the blue line — power consumption at idle — the steeper the decline, the better.

Figure 2 reveals some interesting insights. During the beginning of the decade, the move from one CPU lithography to another, e.g., 65 nanometers (nm) to 45 nm, 45 nm to 32 nm, etc., presented major performance per watt gains (orange line), as well as substantial reduction in idle power consumption (blue line), thanks to the reduction in transistor size and voltage.

However, it is also interesting to see that the introduction of a larger number of cores to maintain performance gains produced a negative impact on idle power consumption. This can be seen briefly during the 45 nm lithography phase and very clearly in recent years with 14 nm.

Over the past few years, while lithography stagnated at 14 nm, the increase in performance per watt (when working with a full load) has been accompanied by a steady increase in idle power consumption (perhaps due to the increase in core count to achieve performance gains). This is one reason why the case for hardware refresh for more recent kit has become weaker: Servers in real-life deployments tend to spend a substantial part of their time in idle mode — 75 percent of the time, on average. As such, the increase in idle power may offset energy gains from performance.

This is an important point that will likely have escaped many buyers and operators: If a server spends a disproportionate amount of time in active idle mode — as is the case for most — the focus should be on active idle efficiency (e.g., choosing servers with lower core count) rather than just on higher server performance efficiency, while satisfying overall compute capacity requirements.

It is, of course, a constantly moving picture. The more recent introduction of the 7 nm lithography by AMD (Intel’s main competitor) should give Moore’s law a new lease of life for the next couple of years. However, it has become clear that we are starting to reach the limits of the existing approach to CPU design. Innovation and efficiency improvements will need to be based on new architectures, entirely new technologies and more energy-aware software design practices.

The full report Beyond PUE: Tackling IT’s wasted terawatts is available to members of the Uptime Institute Network here.

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