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Adaptive Optimization in the Jalapeño JVM

Adaptive Optimization in the Jalapeño JVM Matthew Arnold Stephen Fink David Grove Michael Hind Peter F. Sweeney Presentation by Michael Bond Talk overview Introduction: Background & Jalapeño JVM Adaptive Optimization System (AOS) Multi-level recompilation Miscellaneous issues

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Adaptive Optimization in the Jalapeño JVM

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  1. Adaptive Optimization in the Jalapeño JVM Matthew Arnold Stephen Fink David Grove Michael Hind Peter F. Sweeney Presentation by Michael Bond

  2. Talk overview • Introduction: Background & Jalapeño JVM • Adaptive Optimization System (AOS) • Multi-level recompilation • Miscellaneous issues • Feedback-directed inlining • Conclusion

  3. Background • Three waves of JVMs: • First: Compile method when first encountered; use fixed set of optimizations • Second: Determine hot methods dynamically and compile them with more advanced optimizations • Third: Feedback-directed optimizations • Jalapeño JVM targets third wave, but current implementation is second wave

  4. Jalapeño JVM • Written in Java (core services precompiled to native code in boot image) • Compiles at four levels: baseline, 0, 1, & 2 • Why three levels of optimization? • Compile-only strategy (no interpretation) • Advantages? Disadvantages? • Yield points for quasi-preemptive switching • Advantages? (Disadvantages later)

  5. Talk progress • Introduction: Background & Jalapeño JVM • Adaptive Optimization System (AOS) • Multi-level recompilation • Miscellaneous issues • Feedback-directed inlining • Conclusion

  6. Adaptive Optimization System

  7. “Distributed, asynchronous, object-oriented design” useful for managing lots of data, say authors Each successive pipeline (from raw data to compilation decisions) performs increasingly complex analysis on decreasing amounts of data AOS: Design

  8. Talk progress • Introduction: Background & Jalapeño JVM • Adaptive Optimization System (AOS) • Multi-level recompilation • Other issues • Feedback-directed inlining • Conclusion

  9. Multi-level recompilation

  10. Multi-level recompilation:Sampling • Sampling occurs on thread switch • Thread switch triggered by clock interrupt • Thread switch can occur only at yield points • Yield points are method invocations and loop back edges • Discussion: Is this approach biased?

  11. Multi-level recompilation:Biased sampling Short method Code with no method calls or back edges Long method method call method call

  12. Multi-level recompilation: Cost-benefit analysis • Method m compiled at level i; estimate: • Ti, expected time program will spend executing m if m not recompiled • Cj, the cost of recompiling m at optimization level j, for i ≤ j ≤ N. • Tj, expected time program will spend executing method m if m recompiled at level j. • If, for best j, Cj + Tj < Ti, recompile m at level j.

  13. Multi-level recompilation: Cost-benefit analysis (continued) • Estimate Ti : Ti = Tf * Pm • Tf is the future running time of the program • We estimate that the program will run for as long as it has run so far • Reasonable assumption?

  14. Multi-level recompilation: Cost-benefit analysis (continued) • Pm is the percentage of Tf spent in m Pm estimated from sampling • Sample frequencies decay over time. • Why is this a good idea? • Could it be a disadvantage in certain cases?

  15. Multi-level recompilation: Cost-benefit analysis (continued) • Statically-measured speedups Si and Si used to determine Tj: Tj = Ti * Si / Sj • Statically-measured speedups?! • Is there any way to do better?

  16. Multi-level recompilation: Cost-benefit analysis (continued) • Cj (cost of recompilation) estimated using a linear model of speed for each optimization level: Cj = aj * size(m), where aj = constant for level j • Is it reasonable to assume a linear model? • OK to use statically-determined aj?

  17. Multi-level recompilation:Results

  18. Multi-level recompilation:Results (continued)

  19. Multi-level recompilation: Discussion • Adaptive multi-level compilation does better than JIT at any level in short term. • But in the long run, performance is slightly worse than JIT compilation. • The primary target is server applications, which tend to run for a long time.

  20. Multi-level recompilation: Discussion (continued) • So what’s so great about Jalapeño’s AOS? • Current AOS implementation gives good results for both short and long term – JIT compiler can’t do both cases well because optimization level is fixed. • The AOS can be extended to support feedback-directed optimizations such as • fragment creation (i.e., Dynamo) • determining if an optimization was effective

  21. Talk progress • Introduction: Background & Jalapeño JVM • Adaptive Optimization System (AOS) • Multi-level recompilation • Miscellaneous issues • Feedback-directed inlining • Conclusion

  22. Miscellaneous issues:Multiprocessing • Authors say that if a processor is idle, recompilation can be done almost for free. • Why almost for free? • Are there situations when you could get free recompilation on a uniprocessor?

  23. You’re so hot! Adaptively optimize me all night long! AOS Controller Hot method

  24. Miscellaneous issues:Models vs. heuristics • Authors moving toward “analytic model of program behavior” and elimination of ad-hoc tuning parameters. • Tuning parameters proved difficult because of “unforeseen differences in application behavior.” • Is it believable that ad-hoc parameters can be eliminated and replaced with models?

  25. Miscellaneous issues:More intrusive optimizations • The future of Jalapeño is more intrusive optimizations, such as compiler-inserted instrumentation for profiling • Advantages and disadvantages compared with current system? • Advantages: • Performance gains in the long term • Adjusts to phased behavior • Disadvantages: • Unlike with sampling, you can’t profile all the time • Harder to adaptively throttle overhead

  26. Miscellaneous:Stack frame rewriting • In the future, Jalapeño will support rewriting of a baseline stack frame with an optimized stack frame • Authors say that rewriting an optimized stack frame with an optimized stack frame is more difficult? • Why?

  27. Talk progress • Introduction: Background & Jalapeño JVM • Adaptive Optimization System (AOS) • Multi-level recompilation • Miscellaneous issues • Feedback-directed inlining • Conclusion

  28. Feedback-directed inlining: More cost-benefit analysis • Boost factor estimated: • Boost factor b is a function of • The fraction f of dynamic calls attributed to the call edge in the sampling-approximated call graph • Estimate s of the benefit (i.e., speedup) from eliminating virtually all calls from the program • Presumably something like b = f * s.

  29. Feedback-directed inlining: Results Why? Why?

  30. Talk progress • Introduction: Background & Jalapeño JVM • Adaptive Optimization System (AOS) • Multi-level recompilation • Other issues • Feedback-directed inlining • Conclusion

  31. Conclusion • AOS designed to support feedback-directed optimizations (third wave) • Current AOS implementation only supports selective optimizations (second wave) • Improves short-term performance without hurting long term • Uses mix of cost-benefit model and ad-hoc methods. • Future work will use more intrusive performance monitoring (e.g., instrumentation for path profiling, checking that an optimization improved performance)

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