[KSP] Performance regression vs KAPT about dagger HOT 7 OPEN

Thanks for posting your findings @trevjonez!

I can't say I'm too surprised by this since we've had years to optimize for Javac but haven't really done any optimization for KSP yet (so far we've only been focused on correctness).

I can take a look through the flame charts and see if anything sticks out.

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I am fairly certain with the --rurun flag these should be effectively the same as a clean run of the ksp/kapt tasks. I did it that way to try and get the flame chart to have as little extra noise as possible given the tracing is picking up everything in gradle too.

That said I'll play with the scenarios a bit more tomorrow and setup clean + incremental just to be sure.

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One thing I noticed is that the KAPT flame chart looks like there's incremental processing going on (IncrementalProcessor.process(...)).

It might help to first compare both of them using a clean build with no incremental processing. That way we can rule out if the regression only occurs for incremental processing or also in clean builds.

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I still owe you some repro projects but I did end up rerunning my out of process benchmarks with the latest KSP (1.0.16) and the time is at least consistent now so the time balloon on 1.9.21-1.0.15 was caused by the memory leak in KSP.

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@trevjonez just to clarify, you're seeing the regression in KSP build times are gone with KSP 1.0.16, meaning it's about the same as your build times with Javac now?

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No it still is a big regression from KAPT. but initially it would take like 15 minutes on a clean KSP build then second run on hot daemons would be 30+ and usually OOM crash out before a third run could finish. It was an obvious indication of a memory leak but someone else reported it to KSP and they fixed leak that so now we should be able to get more accurate timing info for the dagger processor optimization.

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Okay, thanks for the clarification on that.

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