Doi: 10.1145/1378727.1378740
The processor is, perhaps, the most obvious target of power management. On a modern system the CPU is likely to be the single component consuming the most power. Switching the state
BY matthe W GaRRett of hundreds of millions of transistors takes power. Modern processors can generate well over 100 watts of heat.
Powering How can this be reduced?
At the most basic level the answer is simple: reduce the power taken to switch those transistors. Making them smaller is one mechanism, as is reducing the amount of power lost via leakage. There are limits, however, to how
Down much power can be saved via fundamental improvements in semiconductor technology, and vendors are being forced to adopt increasingly high-tech solutions to maintain the rate of progress in this respect. We cannot rely on technological breakthroughs to be the silver bullet. We need to be smarter in how we use what we already have available.
The most reasonable approach to reducing the power consumption of processors is to realize that under normal usage patterns processors will not run at 100% utilization all the time. The first attempt to take advantage of this was in the Pentium era with the addition of idle power savings. The HLT (halt) instruction allowed operating systems to indicate that they had nothing to execute, letting the processor put itself into some form of power saving until the next interrupt arrived. Runtime processor power management had arrived.
PHO TOGRAPH BY PAUL TICHONCZUK
The APM (Advanced Power Management) specification extended this functionality. Rather than simply halting the processor, the APM CPU idle call allowed the processor to be put into a lower power state where it continued to execute instructions. If system load reached a threshold level, the operating system could then send a CPU busy call to restore the processor to full operating speed.
This concept of runtime power management has been further enhanced in recent years. CPU clock and volt-
Smart power management is all about doing more with the resources we have.
POWER MANAGEMENT—FROM laptops to rooms full of servers—is a topic of interest to everyone. in the beginning there was the desktop computer. it ran at a fixed speed and consumed less power than the monitor it was plugged into. Where computers were portable, their sheer size and weight meant that you were more likely to be limited by physical strength than battery life. it was not a great time for power management.
Now consider the present. Laptops have increased in speed by more than 5,000 times. Battery capacity, sadly, has not. With hardware becoming increasingly mobile, however, users are demanding that battery life start matching the way they work. People want to work from cafés. Long-haul flights are now perceived as the ideal opportunity to finish a presentation. Two hours of battery life just isn’t going to cut it; users are looking for upward of eight hours. What’s drawing that power, and more importantly, how can we reduce it?
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