Tomba2's Trolley attract demo interprets a working set past 64K distinct
PCs. The per-PC tracking tables (g_dirty_ram_pc_table / exec_pc_table) used
an UNBOUNDED linear probe, so once a table filled, every lookup for an
absent PC scanned all 65536 slots before returning NULL — per executed
instruction. Host thread profile showed ~99% of emu-thread time inside
pc_table_get_or_insert_in; guest crawled at 0.3 fps (1M guest cycles per
3s wall) while telemetry showed the window "LIVE" on residual motion.
Fix: hard-bound the probe to 128 slots (miss => NULL => "stop tracking",
the documented degradation) and grow the tables 65536 -> 262144 so the
Trolley working set actually fits — the same table feeds overlay-capture
seed lists (MAX_CAPTURE_PCS aliases it), so the old size also silently
truncated capture manifests for large regions.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Matthew Stanley
bbe0d2ae8e