Perf numbers are much faster with a warm chrome

[paulirish]

If there's no debugable chrome open (in the CLI case) then we launch one, wait for it, and then start profiling. It appears we're getting overhead from a new profile bootup that's having a big effect on the numbers.

Looking at https://example.com/ which is a superfast site..

Cold chrome:

Warm chrome:

Running chrome-debug and letting it sit for like 5 seconds.

On chat we discovered there's 200kb of data transferred on a cold chrome, seemingly for malware. In addition, there is likely some CPU cost overhead for initializing an empty profile.

Edit: I believe "downloading proxy config" is also responsible for a fair bit of it

I bet a little delay injected in there before the profiling starts would sort this out.

[brendankenny]

(somewhat related to #775, though that's no longer outright affecting us)

[wardpeet]

we could let the cli sleep for a few seconds and show them a message. Warming up chrome :D

[addyosmani]

I bet a little delay injected in there before the profiling starts would sort this out.

Ooof. Yes please.

[wardpeet]

How many seconds are we talking about? + is there a way to see if chrome is cold or warm? Or just delay all the time?

[paulirish]

Discussed this with @caseq and think proxy config is likely a concern here.

Best looking fix at the moment is as follows:

Load http://connectivitycheck.gstatic.com/hello_lighthouse and wait for load. Once loaded, proceed.
(Alternatively, could run our own webserver and put up a basic/blank page.)

[paulirish]

confirmation that it's proxy config:

[patrickhulce]

tracked by #1982