User Guide

Contents

CPU Utilization

Metric Description

This metric evaluates the parallel efficiency of your application. It estimates the percentage of all the logical CPU cores in the system that is used by your application -- without including the overhead introduced by the parallel runtime system. 100% utilization means that your application keeps all the logical CPU cores busy for the entire time that it runs.
Depending on the analysis type, you can see the CPU Utilization data in the Bottom-up grid (HPC Performance Characterization), on the Timeline pane, and in the
Summary
window on the
Effective CPU Utilization
histogram:
For the histogram, the
Intel® VTune™
Profiler
identifies a processor utilization scale, calculates the target CPU utilization, and defines default utilization ranges depending on the number of processor cores. You can change the utilization ranges by dragging the sliders, if required.
Utilization Type
Default color
Description
Idle
Idle
utilization. By default, if the CPU Time on all threads is less than 0.5 of 100% CPU Time on 1 core, such CPU utilization 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
utilization. By default, poor utilization is when the number of simultaneously running CPUs is less than or equal to 50% of the target CPU utilization.
OK
Acceptable (
OK
) utilization. By default, OK usage is when the number of simultaneously running CPUs is between 51-85% of the target CPU utilization.
Ideal
Ideal
utilization. By default, Ideal utilization is when the number of simultaneously running CPUs is between 86-100% of the target CPU utilization.
VTune
Profiler
treats the Spin and Overhead time as Idle CPU utilization. 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 Utilization graphical representation per analysis type.
For the HPC Performance Characterization analysis, the
VTune
Profiler
differentiates
Effective Physical Core Utilization
vs.
Effective Logical Core Utilization
for all systems other than Intel® Xeon Phi™ processors code named Knights Mill and Knights Landing.
For Intel® Xeon Phi™ processors code named Knights Mill and Knights Landing, as well as systems with Intel Hyper-Threading Technology (Intel HT Technology) OFF, only generic Effective CPU Utilization metric is provided.

CPU Utilization vs. Thread Efficiency

CPU Utilization may be higher than the Thread Efficiency (available for Threading analysis) if a thread is executing code on a CPU while it is logically waiting (that is, the thread is spinning).
CPU Utilization may be lower than the Thread Efficiency if:
  1. The concurrency level is higher than the number of available cores (oversubscription) and, thus, reaching this level of CPU utilization is not possible. Generally, large oversubscription negatively impacts the application performance since it causes excessive context switching.
  2. 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.

Possible Issues

The metric value is low, which may signal a poor logical CPU cores utilization caused by load imbalance, threading runtime overhead, contended synchronization, or thread/process underutilization. Explore CPU Utilization sub-metrics to estimate the efficiency of MPI and OpenMP parallelism or run the Threading analysis to identify parallel bottlenecks for other parallel runtimes.

Product and Performance Information

1

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804