CPU usage exceeds 100% in Task Manager and Performance Monitor if Intel Turbo Boost is active

Applies to: Windows 8Windows 8 Enterprise

Symptoms


Starting with Windows 8, a change was made to the way that Task Manager and Performance Monitor report CPU utilization. With this change, CPU utilization may appear to exceed 100% when the system is under a heavy load, especially when capacity is boosted by Intel Turbo Boost.  

Cause


This change affects the way that CPU utilization is computed. The values in Task Manager now correspond to the Processor Information\% Processor Utility and Processor Information\% Privileged Utility performance counters, not to the Processor Information\% Processor Time and Processor Information\% Privileged Time counters as in Windows 7.

More Information


The difference between the two counter types concerns how they measure the actual work that the processor performs. The “time”-based performance counters measure the percentage of time that the processor is busy, whereas the “utility” performance counters measure how much work the processor actually performs. The utility performance counters take into account the processor performance state and Turbo Boost-based enhancements to measure and normalize the work that's being done by the CPU.

This change was intended to provide a more accurate representation of how much work the system is handling, and the utility counters do just that. A processor that’s running 50% of the time and clocked down to 50% frequency performs only half the work of a processor that’s running 100% of the time at 100% frequency. Before this change, under the time-based performance counters (used in Windows 7 Task Manager), those two processors clocked differently. Both appear to be doing the same amount of work: 100% of their capacity. With the redesigned Task Manager, the first processor is shown to be running at 50% capacity, whereas the second processor is shown to be running at 100% capacity. And Turbo Boost drives the processor above 100% of its nominal speed, and allows the processor to exceed 100% capacity.