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>
Handoff snapshot of the env-gated diagnostic scaffolding used across the
intro-video RE. Kept out of the milestone commits (645feb8..5573ac1) to keep
those clean; committed here so nothing is lost on handoff.
New — XENIA_PROFILE wall-time profiler (crates/xenia-gpu/src/prof.rs):
Coarse buckets attributing playback wall time to interpreter (step_block),
kernel HLE (call_export), block decode/cache (lookup_or_build), texture
decode, host draw, and present; prints periodic snapshots (every 500M guest
instr, or every 500 presents) + a clean-exit report. Hot path is gated on a
cached is_on() (one relaxed load) so it is zero-cost when XENIA_PROFILE is
unset. Call sites: main.rs run_superblock / parallel worker (step_block,
lookup_or_build, call_export), texture_cache ensure_cached, render.rs present
+ dispatch_xenos_draws.
First profile (movie playback, headless single-thread lockstep): effective
~35 MIPS; interpreter body ~40% @ ~95-102 MIPS; texture decode 0.3% (cache
works); present ~0%; the rest is per-block dispatch + scheduler plumbing
(~13 instr/block over 229M blocks). Overhead-bound, not interpreter-body
bound; the levers are coarser execution units (superblock chaining) and
ultimately a JIT.
Pre-existing read-only probe knobs (were uncommitted; env-gated, observe-only):
XENIA_RET_CAPTURE_PC/_REG/_MEM, LOG_RESUMES, LOG_WAITS, LOG_SIGNAL,
FORCE_TID, STARVE_LIMIT, INCUMBENT_PICK, INSTR_PER_MS, DUMP_FRAME,
DUMP_WGSL, BIND_LOG, CONST_LOG, DISPATCH_REC, AUDIT_PC_TRACE.
Tooling: sylph-run.sh (movie oracle loop, 180s default timeout),
zq.py (DuckDB disasm/xref helper).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
