HPjmeter 4.3 User's Guide

CPU Versus Clock Time

The clock time is the time as measured by an external independent clock, sometimes also called

wall clock. Clock time includes the time that passes for any state that a thread may be in. That is,

clock time includes the time the thread spends in sleeping, waiting, performing an I/O operation,

waiting for garbage collection to complete, being preempted by the operating system, and in

processing.

CPU time accounts for the time spent by any of the CPUs (processors) on executing a thread. Other

thread states are not counted in CPU time.

A so-called virtual CPU time, usually collected by sampling, is similar to CPU time, but includes

time elapsed while the thread was ready to run, but was not actually scheduled to run by a CPU,

for example, while the thread was preempted. Depending on the platform, virtual CPU time can

also include the time spent in I/O operations.

If the profile data file contains the information about the profiling overhead, HPjmeter adjusts the

measured CPU times by subtracting the time spent by the profiler. Thus, reported times match more

closely those actually used by the Java application.

To inform you about the increased accuracy, a console visualizer will show “times in milliseconds,

adjusted for profiling intrusion)” next to the metric label if the adjustment took place.

Locating Summary Information for Saved Data Sets

Summary data is displayed on the first tab that you encounter when you open a profiling data set

for viewing. This information includes when the application data was collected and for how long,

and a few application conditions present during the collection time.