1698427 - Refactor JS frame extraction out of MergeStacks

Status: RESOLVED FIXED

(Core :: Gecko Profiler, task, P2)

Description

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

This small task moves the JS frame extraction code out of MergeStacks.
This ExtractJsFrames function will be called before MergeStacks, and even before stack-walking.

A later task will extract more data from JS frames, to be passed to stack walkers, to help them resume native walking past JIT frames.

Comment 1

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

Attachment: Bug 1698427 - ExtractJsFrames factored out of MergeStacks - r?canaltinova

Comment 2

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

Attachment: Bug 1698427 - Clean and optimize ExtractJsFrames - r?canaltinova

Some changes after the previous just-move-the-code refactoring:

• Updated functon comment for clarity.
• Moved samplePosInBuffer computation to where it's first needed. Bonus: It won't happen anymore if there is no JS stack.
• Construct jsIter as first for statement, it's clearer that it's the main loop iterator.
• Moved MAX_JS_FRAMES checks into the loop body, and only when needed.
• Moved context retrieval closer to first use. Same in MergeStacks; Note that aRegisteredThread.GetJSContext() is only reading a member variable, so it's cheap enough use it again there if needed, it may even be better overall than storing it in a register or on the stack (if the compiler couldn't optimize it already before).

Depends on D108415

Comment 3

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

Attachment: Bug 1698427 - Call ExtractJsFrames outside of MergeStacks, before native stackwalk (if present) - r?canaltinova

In a later bug, ExtractJsFrames will retrieve more information about the JS frames, which will be given to stack walkers in order to resume native sampling past JIT stacks.

Depends on D108416

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/9129f0dc9f38
ExtractJsFrames factored out of MergeStacks - r=canaltinova
https://hg.mozilla.org/integration/autoland/rev/314767eb5be5
Clean and optimize ExtractJsFrames - r=canaltinova
https://hg.mozilla.org/integration/autoland/rev/e90eebb4095d
Call ExtractJsFrames outside of MergeStacks, before native stackwalk (if present) - r=canaltinova

Comment 5

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/9129f0dc9f38
https://hg.mozilla.org/mozilla-central/rev/314767eb5be5
https://hg.mozilla.org/mozilla-central/rev/e90eebb4095d