HP ML150 ISS Technology Update, Volume 7, Number 8 - Page 2

ISS Technology Update Volume 7, Number 8 Count on the number of CPU cores increasing What's driving the increase in core counts? Historically, the hunger for higher performance has driven major processor innovations. With traditional single-core CPUs, improved performance is possible by increasing the clock frequency and increasing the number of transistors. But increasing the clock frequency leads to greater power consumption and heat generation. Processor power consumption (P) has a linear relationship to clock frequency (f) and a non-linear relationship to the supply voltage (v), as expressed by the equation P=Cv2f, where the total capacitance, C, is proportional to the number of transistors. As the frequency increases, there is an exponential increase in CPU power use (Figure 1 left) because within a particular transistor geometry generation, more voltage must be applied to get transistors to switch on and off at higher frequencies. At higher voltages, transistors experience increased leakage current-current that takes alternate paths through the transistor-resulting in increased heat generation and less efficient operation. From a power perspective, processors are more efficient when they operate below their maximum frequency. This fact combined with constrained facility space and rising power and cooling costs, has caused the market to demand higher CPU performance per watt. This market shift is driving processor vendors to shrink the size of cores. Smaller cores require less power, permitting more cores to be built into a single processor to get more performance out of each silicon chip. Figure 1-1. Power use and heat dissipation increase exponentially with frequency (left), so after 2004, processor vendors began limiting the frequency (right) and increasing the number of cores per chip. What determines the number of CPU cores offered in HP ProLiant servers? HP ProLiant servers include a range of single-core and multi-core processors from Intel and AMD. In determining which processor to offer for each ProLiant server model, HP tries to match the needs of its customers with the processor options available from these two processor vendors. The processor vendors determine the number of processor cores to offer by evaluating market trends while trying to maintain a competitive advantage. Are more cores better? Based on performance-per-watt, low-voltage quad-core processors deliver a cooler and more power-efficient option than processors with fewer cores. However, to take advantage of multiple cores, multi-threaded applications need to be employed. When more multi-threaded applications become available, HP recommends that customers begin to migrate from legacy applications to benefit from the higher performance and increased power efficiency. Alternatively, there are methods to shut down underutilized cores or place them in a low-power state to provide investment protection for tomorrow (see "Optimizing the performance of multi-core processors" in this issue). 2