KSP2 Performance Issues

[ZacSweers]

(Filing at the request of the JB folks for referencing)

I re-profiled our builds with KSP2 with 2.0.21-1.0.27. Unfortunately, across the board in a bunch of benchmarks I found that

• abi change - KSP2 is ~40-50% slower
• noabi change - KSP2 is 80-100% slower
• clean build - negligible/amortized by the clean build

If I just benchmark expensive our two most expensive KSP tasks with `, KSP2 is around 20-30% slower.

Other notes:

• We give the kotlin and gradle daemons the same memory, and these benchmarks were run on overpowered AWS boxes
• None of these builds were experiencing memory pressure with the settings they had (somewhere in the dozens of GB for xmx)

time-to-task-start is more or less the same, assumes a hot configuration cache

Here's a few samples. Looking again there is some GC time creeping into some of these that I'll look closer into, but not enough to majorly skew the larger trend

[bcorso]

I re-profiled our builds with KSP2 with 2.0.21-1.0.27.

@ZacSweers sorry if I missed it, but what is the comparison against?

Is this comparing two different versions of KSP2 or KSP1 vs KSP2 (or something else)?

[ZacSweers]

Comparing against KSP1 yeah

[ZacSweers]

Tested again with 2.1.10-1.0.30 but still seeing significant regressions.

ABI - ~25%-28% slower
non-abi - ~ 40%-50% slower

[ting-yuan]

Hello @ZacSweers, 2.1.20-1.0.32 includes a few performance fixes on the startup time of KSP2. I hope that will help overall performance and especially on non-ABI changes. Please let me know if you're still seeing any kind of performance regressions. I'd really appreciate any data / information that may guide the direction of optimizations.

[ZacSweers]

Tested again with 2.1.20-1.0.32 with mixed results.

TL;DR

• Smaller projects - ~20% faster
• More intensive projects (large classpaths) - still ~15-18% slower

(large classpath + busier processor)

[ansman]

I tried KSP 2 on our large project, and this is the result:

	Longest KSP task	Total time spend in KSP	Total build time
KSP1	13.740s (100%)	14m 24.981s (100%)	5m 57.983s (100%)
KSP2 (1.0.31)	25.218s (184%)	15m 40.957s (109%)	5m 44.658s (96%)
KSP2 (1.0.32)	20.842s (152%)	11m 36.319s (81%)	4m 59.995s (84%)