feature: refactor and extend log_exporter benchmark

[demurgos]

Design discussion issue: #2031

Changes

This commit refactors and extends the log_exporter benchmark.

1. Rename to be more precise: FooWithFuture becomes FooAsyncTrait, FooWithoutFuture becomes FooSync
2. Add variant using native Rust support for async traits
3. Share workload code between implementations
4. Use blackbox hint for implementations under test
5. Expand module documentation
6. Move each impl into its own submodule

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable): N/A
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes: N/A
• Changes in public API reviewed (if applicable): N/A

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.0%. Comparing base (99d24b7) to head (de4ee51).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2143   +/-   ##
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  Coverage   79.0%   79.0%           
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  Files        121     121           
  Lines      20945   20945           
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  Hits       16561   16561           
  Misses      4384    4384           

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[cijothomas]

@demurgos Thanks in advance for your patience! I am clearing my backlog and will get to this soon!

[cijothomas]

can you add this consistently to other ones too, to ensure a fair comparison.

[demurgos]

Oh, I missed the #[inline], I thought I applied it everywhere. I'll update my PR.

[cijothomas]

From the benchmarks, this looks to be close enough with sync counterpart. Wondering if there is a reason we can't try this in the Exporter traits? The <T> for output might make things complex...?
(I only added this benchmarks to see if there is actually some price to be paid for introducing async.)

@demurgos Do you have some bandwidth to modify existing exporter trait to use async native style? The existing benchmarks should show improvement with this change, based on what i observe in this PR.

(Still pretty new to Rust async, so I might be missing something obvious!)

[demurgos]

Hey 👋
I was also interested in trying to impl a version using native async. I'm pretty familiar with it, but the lib is pretty large. I'll try to send something, but I can't promise any timeline.

[cijothomas]

@lalitb Can you help continue this?

[lalitb]

@lalitb Can you help continue this?

Had a quick look. The impl Future approach is indeed much faster (around ~8 times faster in my local tests), which makes sense as it uses static dispatch with future type is known at compile time and so avoids overhead of heap allocations and dynamic dispatch that comes with using Pin<Box<dyn Future>> or async-trait. However, it requires Rust 1.75 or newer since impl Trait in traits was only stabilized in that version. Since our current msrv is 1.71, we can't use this approach without updating our Rust version.

Before going forward, it's good to discuss if we should bump-up our msrv to 1.75 for otel-sdk, and all exporters.