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Weird idle time in the Waterfall - Printable Version

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Weird idle time in the Waterfall - CamiloAPR - 12-15-2020 07:35 AM

Hey everyone. So a couple of weeks ago I was running some tests on WebPageTest, Pingdom and Google Pagespeed Insights to get a general sense of a site's performance. Got relatively normal results on all of them but WebPageTest. on WebPageTest I kept noticing weird idle times between requests. but nothing I've seen before, they were really long idle times. last week I noticed those idle times were gone, but I'm pretty sure they weren't server/code related, as I noticed several sites were getting the same thing. Here's an example:

Result from Nov 24th -> https://i.imgur.com/7ZEWACe.png
Result from Dec 10th -> https://i.imgur.com/6lD28HU.png

Does anyone have a clue about this?, I can't help but think it may have been an issue in WebPageTest (As I said, no other tool had this issue).

RE: Weird idle time in the Waterfall - pmeenan - 12-15-2020 11:43 PM

Do you have links to the test results themselves (can email them to pmeenan@webpagetest.org if you don't want them public)?

The CPU line looks pretty busy at the time so it looks like there was something non-request-based going on (layout would be my guess).

Given the dates and location of the gaps, if the test location was Dulles, I am going to bet it was this: https://github.com/WPO-Foundation/webpagetest/issues/1410

Chrome on Ubuntu 20.04 was having some pathological layout times with some sites so the Dulles agents were re-deployed with 18.04 until I can track down what is going on.

RE: Weird idle time in the Waterfall - CamiloAPR - 12-16-2020 01:00 AM

Thanks for the quick reply!. Yeah. Looks like that might be it. is there something we should keep in mind going forward to avoid this issue?

RE: Weird idle time in the Waterfall - pmeenan - 12-16-2020 01:20 AM

As users you shouldn't have to worry about it now that we're aware it's a problem. Any OS updates in the future now have a decent number of test sites that demonstrate the problem to use for testing before deploying and it won't be deployed if there are issues.