cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 

This product reached the end of support date on March 31, 2021.

CPU Sample - Idle Time, CPU Used Time and Dynatrace Instrumentation CPU Overhead

asahoo1
Organizer

I have attached a CPU sample taken in one of our web servers. The web server CPU usage spiked from 50% to 70% during the time when the sample was taken. However, the CPU sampling overview screen shows dynaTrace instrumentation overhead as just 1%. Can you please help explain the terms CPU Idle time, CPU time and dynaTrace Instrumentation CU Overhead ( I couldn't find any detailed info in the 6.3 Product documentation)?

The server has 8 CPU cores. I have attached the CPU sample below.

cpu-sample-07262016.dts

1 REPLY 1

dennis_mispelba
Inactive

Hi Abhaya,

Dynatrace is keeping measurements for different CPU times:


























CPU I/O
Wait Time
Percentage
of total time the CPU spent waiting for I/O operations.
CPU Idle
Time
Percentage of total time
the CPU was in idle mode.
CPU Other
Time
Percentage of time the
CPU spent in everything else. This includes steal time, interrupt time, and
every unknown time.
CPU System
Time
Percentage of total time
the CPU spent processing system-space programs.
CPU Total
Time
Percentage of total
time the CPU was in use.
CPU User Time Percentage of total time
the CPU spent processing user-space programs.

Now, since the agent knows what it has instrumented in your application, it can derive, how many methods (lines of code) have been needed to go through in addition to your normal application execution. Thus, it can derive the overhead it creates, which is measured in terms of CPU time (overhead Dynatrace created on the CPU).

Depending on your settings, Dynatrace allows different settings as overhead. That is, if this threshold is exceeded, Dynatrace will move down with its auto-sensors, in order to keep below the allowed overhead. You may want to leave this setting to default (in Production this means an allowed overhead of maximum 3%, while in Pre-Prod it means a maximum allowed overhead of 10%), but you could change it within the Agent Group -> Agent Mapping -> Advanced section.

In your case you have 1% overhead, which appears normal/fine to me. From the information you gave, I would argue, your spiking times of the CPU are not caused by Dynatrace. I did not take a look at your DTS file yet, though.

I hope this information helps.

Best regards
Dennis