f3b7e8b760
The lockstep scheduler's pick_runnable is strict priority (max_by_key (priority, -idx)). On a cooperative single-host HW slot, a CPU-bound spinner that never blocks (the silph poll loop pinned by affinity to hw=5) wins pick_runnable every round forever, permanently starving a co-located peer (the submitter, tid6) that the spinner is actually waiting on. On real hardware those threads run on separate SMT contexts concurrently, so the spinner never starves the submitter; ours collapses them onto one slot with no anti-starvation, turning priority (or equal-priority index order) into permanent starvation. The starved submitter never dequeued job-4 -> the worker-hub (tid5) blocked INFINITE on completion event 0x1080 -> silph (tid13) wedged on 0x1078 -> no vsync -> draws_seen=0, the publisher splash never renders. (decrement_quantum's within-slot rotation is dead: begin_slot_visit unconditionally re-pick_runnable()s each round, discarding the rotated running_idx. The fix is therefore evaluated at pick time, not via that discarded rotation.) Fix (Option A, bounded anti-starvation, deterministic): - Add per-thread steps_starved counter to GuestThread. - begin_slot_visit increments it for every Ready peer passed over this visit, resets it to 0 for the picked thread. - pick_runnable selects by effective_priority: once steps_starved reaches STARVE_LIMIT (4096) the thread is lifted to i32::MAX and wins exactly one pick, then resets. The genuinely higher-priority thread still wins ~4095/4096 visits -- the boost grants periodic forward progress only, it does NOT invert priority. Pure function of counter/priority/index -> deterministic (no wall-clock, no RNG). Cascade (lockstep exec, XENIA_CACHE_PERSIST=1, -n 200M): - submitter dequeue sub_82458508 now fires 4x (was 3x); the 4th job (buf 0x40baa2c0) is dequeued at cycle 6.15M. - hub tid5 leaves Blocked(0x1080) -> now Ready (no more INFINITE wait). - GPU packets 0 -> 116,101,363 (command stream now flowing). - tid13 (silph::UImpl) advances past the old 0x1078 wedge to a NEW downstream wait (handle 0x10a0); 3 new threads spawn (tid14/15/16). - draws_seen still 0 -> the splash's first draw is a NEW downstream gate, not this starvation. Determinism: two cold lockstep `check -n 5M` runs byte-identical (full and stable digests). New n50m stable digest deterministic across two cold runs. Golden re-baselined: instructions 50000007->50000003, imports 92317->90296 (trajectory shift from the changed pick order). Tests: 666/666 (+1 test_anti_starvation_bounded_progress). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
11 lines
180 B
JSON
11 lines
180 B
JSON
{
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"instructions": 50000003,
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"imports": 90296,
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"unimpl": 0,
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"draws": 0,
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"swaps": 1,
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"unique_render_targets": 0,
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"shader_blobs_live": 0,
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"texture_cache_entries": 0
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}
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