For the user-mode sampling and tracing analysis types, the Intel® VTune™ Amplifier identifies a processor utilization scale, calculates the target CPU usage, and defines default utilization ranges depending on the number of processor cores. You can change the utilization ranges by dragging the slider in the Summary window.
Utilization Type |
Default color |
Description |
|---|---|---|
Idle |
|
Idle usage. By default, if the CPU Time on all threads is less than 0.5 of 100% CPU Time on 1 core, such CPU usage is classified as idle. Formula: ∑i=1,ThreadsCount(CPUTime(T,i)/T) < 0.5, where CPUTime(T,i) is the total CPU Time on thread i on interval T. |
Poor |
|
Poor usage. By default, poor usage is when the number of simultaneously running CPUs is less than or equal to 50% of the target CPU usage. |
OK |
|
Acceptable (OK) usage. By default, OK usage is when the number of simultaneously running CPUs is between 51-85% of the target CPU usage. |
Ideal |
|
Ideal usage. By default, Ideal usage is when the number of simultaneously running CPUs is between 86-100% of the target CPU usage. |
CPU usage may be higher than the thread concurrency if a thread is executing code on a CPU while it is logically waiting (that is, the thread is spinning).
Note
In the CPU Usage histogram provided in the Summary window, the VTune Amplifier treats the Spin and Overhead time as Idle CPU usage. Different analysis types may recognize Spin and Overhead time differently depending on availability of call stack information. This may result in a difference of CPU Usage graphical representation per analysis type.
CPU Usage may be lower than the thread concurrency if:
The concurrency level is higher than the number of available cores (oversubscription) and, thus, reaching this level of CPU usage is not possible. Generally, large oversubscription negatively impacts the application performance since it causes excessive context switching.
There was a period when the profiled process was swapped out. Thus, while it was not logically waiting, it was not scheduled for any CPU either.
Note
You may set the color scheme to colorblind from
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Intel VTune Amplifier
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pane. The colors of the utilization types will be shown in greyscale.