Recently the profiler settings were changed to collect screenshots by default. However, this has a very large performance impact on rendering performance (at least, in the case with WebRender enabled, I haven't check other backends).

For example, in https://perfht.ml/2yGi5yn (supplied by a user for https://bugzilla.mozilla.org/show_bug.cgi?id=1636604) you can see that the majority of time spent in the WR 'Renderer' thread is taking screenshots. This obscures or makes it hard to identify from a user profile what the WR performance would be like in normal usage.

Could we consider either:

• Switching to the old behavior - screenshots are disabled by default (my preference), or
• Add some kind of graphics / performance preset we can suggest users enable, which disables screenshots.

Another reason to have them disabled by default is that they currently permanently turn of the WebRender compositor/DirectComposition for the rest of the session. This causes a permanent performance loss and also makes the profile less reflective of reality.

Hey Greg, what do you think?

Severity S3 because there's a workaround (disabling manually) and it's low impact. But this is still painful for users because a user can't save presets so the change needs to be done all the time.

I may being pedantic, but I disagree that this is a defect, but is just different user needs, so I would categorize this as an "enhancement".

I filed Bug 1640183, since it sounds like the issue is "I'm asking a user to use the profiler the way I want". I think we should provide a way to do that. In addition, I think we should surface the screenshots option in the profiler popup, since it's one that causes a non-trivial amount of overhead. I still think it should be on by default in the common case since the screenshots are so useful. However, with Bug 1640183 this would remove the friction of asking a user to record a profile. I'm also fine adding more presets.

I also filed: Bug 1640187 to add a screenshots checkbox.

I think the current Graphics preset fulfills this need, especially it has screenshots disabled.