1714888 - DAMP Perf improvement in objectexpand many instances

Status: RESOLVED WONTFIX

(DevTools :: Object Inspector, task, P3)

Description

[Julian Descottes [:jdescottes]]

There is an unexpected 30% perf improvement on console.objectexpand-many-instances, confirmed after doing a compare using only Bug 1499679:

https://treeherder.mozilla.org/perfherder/comparesubtest?originalProject=try&newProject=try&newRevision=1f427250535471bb3c6f72903c28329334f15c8a&originalSignature=3165836&newSignature=3165836&framework=12&originalRevision=69adf280c487ed7e22d021598af4efe65e8519fe

Nicolas, you mentioned that this should not have improved the perf for this test. Do you want to investigate this and check if we haven't regressed the test or anything else?

Comment 1

[Nicolas Chevobbe [:nchevobbe]]

I was able to confirm that the improvement was introduced by https://hg.mozilla.org/mozilla-central/rev/f1b290559447 , which is the server-side part of the patch.
It introduced an early return when the OBJECT_PREVIEW_MAX_ITEMS is reached, meaning we won't start iterate over the symbols (and avoid calling objectActor._propertyDescriptor, at least once), so that might explain the improvement on the test, which makes use of a lot of symbol properties.

Comment 2

[Julian Descottes [:jdescottes]]

(In reply to Nicolas Chevobbe [:nchevobbe] from comment #1)

I was able to confirm that the improvement was introduced by https://hg.mozilla.org/mozilla-central/rev/f1b290559447 , which is the server-side part of the patch.
It introduced an early return when the OBJECT_PREVIEW_MAX_ITEMS is reached, meaning we won't start iterate over the symbols (and avoid calling objectActor._propertyDescriptor, at least once), so that might explain the improvement on the test, which makes use of a lot of symbol properties.

Thanks for the investigation, I don't think we will follow up on this in that case.