Detecting Processor Bottlenecks

The symptoms of a processor bottleneck aren't difficult to recognize:

• Processor: %Processor Time often exceeds 90%.
• System: Processor Queue Length is often greater than 2.
• On multiprocessor systems, System: % Total Processor Time often exceeds 50%.

But these symptoms don't always indicate a processor problem. And even when the processor is the problem, adding extra processors doesn't always solve it. In this chapter, you'll learn to use Performance Monitor to analyze such symptoms, determine the likely cause of processor bottlenecks, and implement effective solutions.


Note Before upgrading or adding processors, verify that the processor is the source of problem. Memory shortages, by far the most common bottleneck, often masquerade as high processor use

The Idle Process

Processors never rest. Once powered up, they must always be executing some thread of instructions. When not executing the thread of an active user or system process, they execute a thread of a process called Idle.


The Idle process has one thread per processor. It has such a low base priority that it runs only when nothing else is scheduled to run. This process does nothing but occupy the processors until a real thread is ready to use them. On a quiet machine, when you would expect processor use to be very low, the Idle process will be using most of the processor time.


Performance Monitor and Task Manager both use the Idle thread to indicate that the processor is not busy. Processor: % Processor Time, System: % Total Processor Time, and Task Manager's CPU Usage and CPU Usage History all measure the Idle thread and display processor busy time as the difference between the total time and the time spent running the Idle thread. Performance Monitor's Process: % Processor Time for the _Total instance even includes time processing the Idle thread.


To measure the Idle thread, use the Process: %Processor Time counter for the Idle process, or use the Processes tab on Task Manager.