Speed frontier, increment 1 (measure-first, then bank the cheap win).
Profiler (crates/xenia-gpu/src/prof.rs): extend XENIA_PROFILE with hierarchical
attribution of the single-thread lockstep loop — ROUND (per-round tax) /
PROLOGUE (worker_prologue) / RUNSB (run_superblock) top level, plus the
STEP/EPILOGUE/KERNEL/BUILD subsets. Gated zero-cost via is_on() (off-check emits
0 lines). Movie-time split: interp step_block 42%, run_superblock chain-loop
body ~30%, worker_prologue+epilogue ~22%, kernel HLE 6%, per-round tax 0.6%,
texture 0.4%. => overhead-bound; the ceiling is a JIT (attacks the ~72% interp
+ dispatch). The per-round tax is a non-lever (0.6%).
Budget (crates/xenia-app/src/main.rs SUPERBLOCK_INSTR_BUDGET 128->192): the
per-slot-visit tax (prologue+epilogue ~22%) scales with slot-visit count, and
chains are NOT break-limited here — 128->192 cuts visits 27.4M->18.9M (-31%),
128->256 -44%. Banked 192 (not 256): the movie decode pipeline is more
timing-sensitive than boot. At 256 the decode worker tid25 (0x82506588)
intermittently fails to resume (1-of-2 runs) with a weakened feeder loop
(source-read 27->5-11) — a scheduling race the coarser interleaving exposes.
192 is deterministic and safe: 3/3 runs byte-identical (source-read=21,
tid25-resume=1, ADVreads=30) at both env-override and compiled-default, ~-7%
movie wall, well below the 384 boot cliff. XENIA_SUPERBLOCK_BUDGET still
overrides for A/B.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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