1609487 - FunctionTree vector growBy is taking almost 1% of profile time in Parse microbenchmark

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P1)

Description

[Matthew Gaudet (he/him) [:mgaudet]]

Using this patch by nbp, as well as his fork of the real-js-samples repo and experimentation code, perf profiling a shell build shows 0.89% of execution time inside of mozilla::Vector<js::frontend::FunctionTree, 0ul, js::TempAllocPolicy>::growStorageBy

There's an opportunity to improve this (at a memory cost) by providing a non-zero MinInlineCapacity.

Comment 1

[Matthew Gaudet (he/him) [:mgaudet]]

Attachment: ChildrenCounts.patch

Comment 2

[Matthew Gaudet (he/him) [:mgaudet]]

Attachment: ChildrenCount.plot.png

Comment 3

[Matthew Gaudet (he/him) [:mgaudet]]

I just did a quick experiment to get a feel empirically what would be a good MinInlineCapacity for FunctionTree by dumping the number of children using Yoric+nbp's benchmarking system. The patch and results are attached. Note the log-10 Y axis scale.

As expected, the number of leaf FunctionTreeNodes is dramatically higher than any other count. We could still make the argument that a non-zero MinInlineCapacity makes sense, but as expected it may come with a memory tradeoff.

Next I'll experiment with performance.

Comment 4

[Matthew Gaudet (he/him) [:mgaudet]]

Ah -- funny story. We can't use MinInlineCapacity here because the Vector definition is within FunctionTree itself, and if you have a non-zero MinInlineCapacity, then Vector<T> needs sizeof(T), which isn't a complete type at that point.

LinkedList from mftb isn't a drop-in replacement either.

For giggles I tried std::list (not shippable due to OOM behaviour): Found no performance change.

Comment 5

[Ted Campbell [:tcampbell]]

We are going to remove the FunctionTree in Bug 1635976 so hopefully this is resolved by it.

Comment 6

[Ted Campbell [:tcampbell]]

Matt, can you sanity check this is resolved?

Comment 7

[Matthew Gaudet (he/him) [:mgaudet]]

Just ran a perf profile: No more interesting stencil related symbols anywhere near the top.