I am seeing pretty bad performance in KSP compared to KAPT t

Question

I am seeing pretty bad performance in KSP compared to KAPT that is fairly concerning version 1 5 31 1 0 0 I am just about done migrating Epoxy to support KSP via XProcessing <https github com airbnb epoxy pull 1244> and took some time to benchmark ksp vs kapt via both gradle build scans and manual timing print statements in the processor All of our processors now support both ksp and kapt and I can switch between modes to compare them but numbers are much worse on KSP for clean builds Here are processors timings we manually logged for a clean build of one of our larger modules Paris 1100ms kapt 3600ms ksp 3 27x slower Epoxy 675ms kapt 4800ms ksp 7 1x slower another in house processor 375ms kapt 1800ms ksp 4 8x slower Even with taking kapt stub generation into account KSP does worse when looking at gradle tasks ksp mode kspDebugKotlin 18 992s kapt mode kaptDebugKotlin 5 652s kaptGenerateStubsDebugKotlin 3 814s I haven t done any in depth profiling yet to know where this comes from not sure if it would mainly be xprocessing or KSP itself Room uses xprocessing though and claimed 2x speed increase so I m curious if that is still correct or if maybe there was a regression I believe we used to actually see better performance with KSP a few months ago

yigit · Answer

i wonder if you can adopt these scripts and run with it

yigit · Answer

not relevant to your case but one mistake i made was relying on gradle profiler s ABI change which actually didn t change the ABI in a way KAPT would be invalidated

yigit · Answer

also you should definitely count KAPT stub time in your comparisons since that is what makes KAPT clean compilation slow

elihart · Answer

thanks for the scripts I d love to get a flamegraph to dig into where the time is going I m doing clean builds with a command on loop like this ` gradlew module clean module assembleDebug no build cache` even with stub generation taken into account ksp is twice as slow but I believe KSP claimed that even without stub generation KSP should be faster because they can do more granular type resolution on demand

yigit · Answer

Not sure about that because kotlin type system is more complex than Java

yigit · Answer

The first script i linked will give you a flame graph but to invalidate abi for KAPT you will need my custom gradle profiler build I might dig that up

yigit · Answer

The interesting case i found there was gradle profiler invalidates abi by addinga public method to a file which did invalidate KSP but didn t invalidate KAPT as it turns them into Java files hence the original annotated file stays unmodified

elihart · Answer

shouldn t matter for clean build profiling though

yigit · Answer

nope

yigit · Answer

let me see if i can find the results

yigit · Answer

just ran that ksp kapt comparison script ``` totals kapt 53759 ms ksp 33144 ms taskTotals kaptWithKaptDebugAndroidTestKotlin 22754 ms kaptClasspath kaptWithKaptDebugKotlin 0 ms kaptClasspath kaptDebugKotlin 1 ms kspWithKspDebugAndroidTestKotlin 32804 ms kaptAndroidTestWithKapt 329 ms kaptGenerateStubsWithKaptDebugAndroidTestKotlin 30438 ms kaptAndroidTestDebug 0 ms kapt 1 ms kaptAndroidTest 0 ms kspAndroidTestWithKsp 319 ms kaptGenerateStubsWithKaptDebugKotlin 80 ms kaptWithKaptDebugKotlin 41 ms kaptGenerateStubsDebugKotlin 50 ms kspWithKspDebugAndroidTestKotlinProcessorClasspath 21 ms kaptDebugKotlin 37 ms kaptWithKapt 0 ms kaptDebug 0 ms kaptWithKaptDebug 0 ms kaptAndroidTestWithKaptDebug 0 ms kaptClasspath kaptWithKaptDebugAndroidTestKotlin 28 ms ````

elihart · Answer

thanks for checking good to see Room is still faster I m trying to get a flame graph with the gradle profiler it s also interesting to see that without the stubs task direct comparison of kapt vs ksp is roughly 50 different so that helps me set expectations for my processors

elihart · Answer

I got a jprofiler flamegraph working happy to share it if anyone is interested in the data xprocessing s `getDeclaredMethods` takes a significant amount of time in large part I think because of forces type resolution for this ``` if it receives or returns inline drop it we can re enable these once room generates kotlin code it parameters any it type resolve isInline || it returnType resolve isInline == true``` similarly `syntheticGetterSetterMethods` checks type for inline functions I suppose anywhere that xprocessing currently resolves type should try to be deferred as much as possible that s really wasteful for my specific use case I m not sure how flexible you want to make the xprocessing api s it might be easier to have an escape hatch to expose the ksp resolver so we can do efficient things when we know we re in ksp right now I access the resolver reflectively but it would be nice to have a real api similarly maybe access to modifiers should be deferred more for example getting all methods forces creation of modifiers when we could probably defer knowing whether its a suspend function ``` return if declaration modifiers contains Modifier SUSPEND KspSuspendMethodElement env containing declaration else KspNormalMethodElement env containing declaration ``` Also accessing rawType seems to not defer creation of type name ```constructor original KspType this ksType = original ksType starProjection makeNotNullable typeName = original typeName rawTypeName ``` and that is a big chunk of my flame graph I think addressing those two things should help me a lot actually

elihart · Answer

In KSP itself there is a lot of time spent in `getSymbolsWithAnnotation gt resolveToUnderlying` which I suppose is to be expected but would be great if some optimizations could be done eventually

Jiaxiang · Answer

Thanks for doing performance evaluation we will address performance issues as part of our plan Speaking of `getSymbolsWithAnnotation` the overhead comes from resolving annotation type we do have some optimizations in place before calling `resolveToUnderlying` we will look into if we can put more optimization but my guess is it is most likely marginal since a type resolution is unavoidable unless we can improve performance for type resolution

elihart · Answer

thanks yes it seems type resolution is mostly needed I think the largest room for optimization is in xprocessing

Ting-Yuan Huang · Answer

re `getSymbolsWithAnnotation gt resolveToUnderlying` Looks like the optimization check simple name before resolution for Java sources is failing This is a huge performance hit because it basically resolves all annotations in Java sources We ll fix it in KSP 1 0 1 <https github com google ksp issues 707>

yigit · Answer

< elihart> can you file them as bugs also does your code never need those resolutions Flame graphs might sometimes be misleeading if you eventually read those values

elihart · Answer

gt does your code never need those resolutions yes in many cases we either only need names or are filtering the methods fields so it is wasteful to resolve all of them

elihart · Answer

I ll file a bug

yigit · Answer

i guess that lazy resolution wasn t a problem for room because most things we read pojos daos we need them all that being said it will probably help room as well as for entities sometimes they are not value objects so we might be reading more than we need possibly insignificant though might be significant for dagger as well

yigit · Answer

< elihart> do you have any of your profiles merged into any of those projects using xprocessing wondering if there is an easy way for me to take a look

yigit · Answer

profiler scripts

elihart · Answer

I ran this on a large module in our airbnb android project But I did it with the standard gradle profiler with jprofiler `gradle profiler profile jprofiler jprofiler config sampling all scenario file profiling scenarios` With a `profiling scenarios` file like ```default scenarios = profiling profiling title = Profile ksp tasks = kspDebugKotlin cleanup tasks = clean gradle args = no build cache Dkotlin compiler execution strategy=in process daemon = none ```

elihart · Answer

I can send you a jprofiler file if you like though

yigit · Answer

thumbsup i wanted to run them myself

yigit · Answer

actually if you can share the profiler result with yboyar google that would be nice i made some small changes but not resolving them does not seem to help much maybe it is a different path

yigit · Answer

also greatly struggling w picking a benchmarking library for this so suggestions are welcome there I need the API similar to androidx benchmarking that will allow me to stop start measurements JMH does not seem to provide that not very faimilar though

yigit · Answer

ok so i did some simple tight look of getting raw types and making it lazy does seem to help based on an async profiler output don t have proper benchmarks yet so it does feel a bit uncomfortable yet slightly smiling face

yigit · Answer

but when i try to measure actual time spent it does not seem to be getting better which does not make much sense need to dig deeper or better figure out how to setup jmh to run some of these properly

elihart · Answer

thanks for starting to look at this so quickly I don t have a benchmark library to recommend but I will email you my jprofiler file

yigit · Answer

this is how i m measuring it to be honest relying on profile is not great but that is the best i have for now

elihart · Answer

great start thanks