Bubo is an experimental implementation of late‑compiler‑stage instrumentation for the Graal just‑in‑time compiler.
It injects probes only in the low‑tier Graal IR, after almost all high‑ and mid‑tier optimisations have run, so the collected profile resembles an uninstrumented run‑time execution. The idea originates from work by Optimization-Aware Compiler-Level Event Profiling and Towards Realistic Results for Instrumentation-Based Profilers for JIT-Compiled Systems
| Challenge with traditional profilers | How Bubo addresses it |
|---|---|
| Probes inserted at bytecode or high‑tier IR interfere with inlining and other optimisations. | Probes are added in the final Graal low tier, so prior optimisations stay intact. |
| Instrument‑everything profilers often impose 80× overhead. | With an cycle threshold for “tiny” methods, Bubo shows a a much lower overhead on the AWFY suite |
| Tiny hot methods suffer when the probe is costlier than the code. | For units whose estimated cost is below 80 cycles, Bubo merely counts activations and estimates cycles from Graal’s own per‑node model |
| Sampling profilers avoid overhead but can miss short‑lived hot spots and suffer safepoint bias. | Bubo records nearly all cycles exactly (RDTSC), while still keeping low overhead. |
- Metadata phase (high tier) – gather compilation‑unit IDs and inlining maps; no probes yet.
- Instrumentation phase (low tier) – insert
ClockNodebefore/after each compilation unit; fall back to lightweight counter probes for units below the threshold. - Accounting & report – aggregate cycle deltas in a JVM‑side buffer; emit a plain‑text profile at JVM shutdown.
This repository is a functional fork of oracle/graal.