1. Adaptive Optimization in the Jalapeño JVM
M. Arnold et al.
Presented by D. Spoonhower
5 March 2003

2. Background Why JIT? JIT vs. Adaptive JRVM: Compile-only
Performance
Safety
JIT vs. Adaptive
Cost/benefit analysis
Feedback-driven
JRVM: Compile-only
Compare to HotSpot, et al.
JRVM: “99%” Java
Modular design, simple implementation
Self-optimizing
Why? Java has no registers
99% Java: class loader, object allocator, baseline compiler

3. Jalapeño AOS Overview Sampling-independent, e.g.
Hardware monitors
Invocation counters
Path profiles
Multiple optimization levels
Baseline – no register allocation
OptLevel0 – “on-the-fly”
OptLevel1 – flow-based
OptLevel2 – SSA (w/ arrays)
Profiling-based optimizations
Simple heuristics

4. AOS Architecture Runtime Measurement System Controller
Raw data collection
“Organizers”
Controller
Direct measurement
Including intrusive profiling
Manage recompilation
Recompilation System
Plan = optimization + profiling data + instrumentation
AOS Database

5. Recompilation: Sampling
Invocation count
Sample at context switch
Yield points in prologues and back edges
Low overhead
Setup:
Method listener
Hot method & decay organizers
Adaptive threshold
Set sample size
Set hotness threshold

6. Recompilation: Cost/Benefit Analysis
For each method m at opt level i:
Ti, future running time of m
Cj, cost to recompile to level j, for i ≤ j ≤ N
Tj, future running time of m if recompiled at level j
Choose j to minimize Cj + Tj and ensure that Cj + Tj < Ti

7. Recompilation: Estimates
Program will execute for twice current duration,
Tf = total future time
Sample to predict percent of time used by m (Pm) and compute:
Ti = Tf * Pm
Offline measurements for speedup:
Tj = Ti * Si / Sj
Use offline configuration of Cj

8. Feedback-directed Inlining
Approximate dynamic call graph
Listener samples in prologue
Caller + call site + callee
Adaptive threshold
Start high and decay
Estimate benefit: boost factor
Fraction of dynamic calls at site
Offline analysis of inlining
Correctness?

9. Opportunities New measurements? New optimization? New cost analysis?
Alias tracking?
New optimization?
arraycheck or castcheck?
New cost analysis?
CPU utilization?
Fewer configuration parameters?
Source available at:
(Now called “Jikes RVM”)