772492 - Clicking 'Analyze' in the SPS Profiler on Windows creates 10-50ms of jank that shows up in the profile

Status: RESOLVED WONTFIX

(Core :: Gecko Profiler, defect)

Description

[Katelyn Gadd (:kael)]

So, 

http://people.mozilla.com/~bgirard/cleopatra/?report=AMIfv94Yz5v-HTiqbaQh-DJUtd8Wviw3WgMelhNifnMRMgzYvZ1uV96VeD-HJBH5e3K0Y6Fba1u_owih-2u00PQS_Lgyytv_zDIZKpYDD9ZLODQWQxB7afXZ958b82tFeYh5ngQ1bwMTt8kGodT1wtllwFo_l1Rpgw

This is a narrowed version of a profile from SPS on Windows. The call stack you see here are some proxy resolutions that are triggered by the network traffic to load Cleopatra (loading css, html, script, etc). For some reason this is happening synchronously on the main thread. That's not great, but the real problem is:

When you click Analyze, the first thing that happens is Cleopatra loads... and THEN it captures the current profile buffer and starts parsing it. This means that you get some unknown amount of garbage at the tail of your current profile buffer that throws off all your statistics. And since Cleopatra's JS isn't always going to be on the stack, it's very difficult to realize that this is being caused by the profiler itself.

This also means that if you hit Stop after hitting Analyze, sometimes Cleopatra loses the race and fails to load your profile data.

I confirmed this by setting a breakpoint on proxy resolution and seeing that the URI the proxy is being resolved for was cleopatra (on people.mozilla.com).

Comment 1

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

Obsolete.