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The Graal compiler is known to be slow in terms of warmup. At the same time, it provides great peak-performance. However, and as you can see in the video, partial evaluation will trigger recompilation if the program is not "stable". And when you're interacting with an IDE, it will take quite some time for the IDE to become stable. Even worse, some things like debugging sessions will never be stable.

Of course, it doesn't make much sense to run your IDE at +60FPS. Squeak usually throttles the frame rate, and then the performance cliffs are harder to notice.

Nonetheless, the GraalVM team is very much aware of these problems and is actively working on them. We are only the first to visualize this in the form of an IDE. A couple of GraalVM releases ago, they introduced libgraal [1], which improved compilation times significantly. One idea to make this even better is to persist compiled code from the JIT, so that it can be reused the next time you run the program/IDE. Morphic, Squeak's UI framework, is unlikely to change and could be warmed up in advance.

[1] https://medium.com/graalvm/libgraal-graalvm-compiler-as-a-pr...

1 comments

Truffle team lead here. Yes we are working full steam on improving warmup and delays caused by going back to the interpreter in unexpected cases. Expect bigger improvements in this area soon.

That being said, we cannot do it all on the Truffle side without help of the language implementation. Truffle languages speculate on certain aspects of the program data. If they do so, then we need to deoptimize and invalidate the optimized code when this speculation is violated. So the stability of the language implementation really is an important factor. Questions like "do we need to speculate on this value being constant or does give us enough benefit to justify the deoptimization overhead?" need to be answered by the language implementation and not the Truffle framework. Afaik this was not a priority for TruffleSqueak so far, but it might be in the future. So there are potentialy future improvements also on the TruffleSqueak side.

I had no idea speculation was surfaced up through Truffle. That's so cool.

Well, it is necessary to expose this to language implementations to reach good performance. If we could reach the same performance otherwise, we would not expose it, as it makes implementing Truffle languages more complicated. Unfortunately automating the specializing part is an unsolved research question for a method based compiler (deserves its own PhD). Other trace based meta-compilation approaches (e.g. PyPy) have an advantage here, but disadvantages in other areas.