The invention relates to power management in a computer system. More particularly, the invention relates to reducing power consumption of microprocessors in a computer system.
Reducing power consumption in computer systems is highly desirable. Reduced power consumption decreases the heat generated by the system. As the packaging of computer systems becomes more compact, the dissipation of heat generated by the system is difficult. Accordingly, it is desirable to reduce the generated heat by reducing power consumption. Additionally, portable or handheld computer systems usually rely on portable power supplies or batteries. Lower power consumption prolongs the usage of a single battery or power supply without a recharge.
The clock frequency of a microprocessor has a highly correlated relationship with the power consumption. The same microprocessor running with a higher clock frequency consumes more power and produces more heat than the same microprocessor running with a lower clock frequency. A typical computer system fixes the clock frequency of its microprocessor at initialization. Therefore, instead of running at the initialized clock frequency in both busy or idle modes, it is better to switch the system to a lower clock frequency if the computer is in an idle mode. One approach to triggering a reduction in clock frequency is to monitor inputs from input devices, such as a keyboard, mouse, or trackball. If there is no input from any of the input devices, for a predetermined period of time, the system will automatically switch from a normal system clock frequency to a slower one. The clock frequency returns to normal when the system receives an input from an input device, such as a keystroke or mouse movement. The input monitoring approach has drawbacks. Although the computer is not receiving an input, it may be engaged in heavy data processing, which a reduced clock frequency hinders this heavy processing.
Another approach for triggering a reduction in clock frequency is to analyze the number of instructions executed by the microprocess for a predetermined period of time. If the number of executed instructions is low, the clock frequency is reduced. If the number of executed instructions increases, the clock frequency is increased to normal. One drawback to analyzing past instruction execution is that the past number of instructions may not accurately reflect future processing requirements. Accordingly, it is desirable to have alternate approaches to reduce power consumption.
A computer system has a processor and a queue for storing instructions for execution by the processor. The processor is capable of being clocked at a plurality of different clock frequencies. A number of instructions in the queue is measured. A particular clock frequency is selected for the microprocessor based on in part the determined number of queued instructions.