CPU Utilization

WebPageTest General Discussion
1

I’m really confused about the “CPU Utilization” chart which is shown on the test result page since I found different interpretations of this chat in this forum:

  1. Some posts in this forum state that this is chart shows client side (browser) CPU utilization caused by javascript execution etc…:

https://www.webpagetest.org/forums/showthread.php?tid=256

  1. Other posts claim this this chart shows CPU utilization on the server:

https://www.webpagetest.org/forums/showthread.php?tid=977
http://www.webpagetest.org/forums/archive/index.php?thread-5529.html

Which of these interpretations is true? From my personal experience would opt for the second option since CPU Utilization varies a lot depending on test location.

Can someone please clearify?

2

It is the client side CPU utilization on the test machine that is loading the page (not the WPT test server which just servs the WPT web UI). It will vary by location because not all of the locations are running the same hardware (unless you only test from the EC2 locations).

3

Thanks for your quick reply. Just to be more precise:

With “test machine” you refer to the virtual machine which hosts the browser, right?

I read in another thread that CPU Utilization refers only to the CPU utilization of the browser process on the virtual machine, but I think it refers to the overall CPU Utilization of the machine?

4

Yes and it refers to the overall CPU utilization of the machine (across all cores).

FWIW, there is also the “Browser Main Thread” utilization that shows up for mobile tests and for Chrome tests with the timeline enabled: https://www.webpagetest.org/result/170112_JE_4969939127ef77bbf6e72da062ce903c/1/details/#waterfall_view_step1

That is specifically just the main browser thread and it’s utilization (in case there was confusion).

5

Thanks a lot! That’s the info I needed.