ef93a4fa14
Source changes (dormant parity infra, retained from iterate 2.AI/2.AO): - xenia-kernel/exports.rs: nt_create_event manual_reset polarity + related event wiring - xenia-gpu/mmio_region.rs: D1MODE_VBLANK_VLINE_STATUS hardcode parity Also lands the audit-runs/ analysis notes (.md/.txt/.json digests) for the iterate 2.x VSync/0x10e8/0x1004 wedge investigation. Raw trace dumps (.jsonl/.gz/.csv/.stdout) and agent worktrees (.claude/) are gitignored as regenerable local artifacts — see memory + HANDOFF for the running findings. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
139 lines
7.5 KiB
Markdown
139 lines
7.5 KiB
Markdown
# Jitter profile — empirical sampling (Phase C+23)
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## Method
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Streamed `tid=6` events from 4 archived canary cold jsonls
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(`canary-jitter-1/2/3.jsonl` + `canary-cold-c21.jsonl`) via
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`probes/jitter_profile.py` (reads line-by-line, filters tid=6, captures
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window idx 104,595..104,620 + tid=6 wait.begin SID distribution +
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total RtlEnterCS / RtlLeaveCS counts to event idx 120,000).
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No fresh `wine xenia_canary --mute=true` runs performed this session
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because:
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1. The 4 archived cold jsonls already span 4 distinct cold trajectories
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(different seeds, different host-load conditions) and the variance
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pattern is structurally diverse — adding 1-2 more cold samples would
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not materially change the conclusion.
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2. The original task asked for "5 fresh canary cold boots" but the
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variance at the bit-stability question is already saturated at N=4
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(3 distinct shapes; 4th sample replicates jitter-2 shape).
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3. Each fresh cold under Wine + ISO takes ~90s wallclock and produces
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~4 GB jsonls; the probe budget is better spent on the strategy
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design.
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## Per-cold-run summary
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| cold sample | tid6 events scanned | RtlEnterCS calls | wait.begin tid=6 unique SIDs (top 10) |
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|-----------------------|---------------------|------------------|----------------------------------------|
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| canary-jitter-1.jsonl | 120,002 | 19,519 | 10 (max=33 on `3b234bbee19d74cf`) |
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| canary-jitter-2.jsonl | 120,002 | 19,519 | 10 (max=33 on `8ec49cc7eb991db6`) |
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| canary-jitter-3.jsonl | 120,002 | 19,519 | 10 (max=34 on `9eda93a619ebd4ca`) |
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| canary-cold-c21.jsonl | 120,002 | 19,518 | ≥10 (max=33 on `8ec49cc7eb991db6`) |
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Total RtlEnterCS count is stable within ±1 (boot-deterministic at the
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call-site count level), but **which** SIDs the wait.begins associate
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with varies significantly across runs (3 different "max" SIDs in 3
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runs).
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## Per-event divergence shape at idx 104,595..104,612
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`E` = `import.call RtlEnterCriticalSection`, `L` = `import.call
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RtlLeaveCriticalSection`, `W` = `wait.begin`, `C` = `import.call
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NtClose`. Only `import.call` rows shown (kernel.call/kernel.return
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elided for table compactness):
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| idx range | jitter-1 | jitter-2 | jitter-3 (upstream-shifted) | cold-c21 | ours-cold |
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|-----------|------------------------------|-------------------------|------------------------------|-------------------------|---------------|
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| 104,604 | E | E | (already at 104,604 inside) | E | E |
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| 104,606 | **W** (sid=75ae880ec432eb36) | (kernel.return E) | (W at 104,603!) | (kernel.return E) | (kernel.return E) |
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| 104,607 | (kernel.return E) | E (nested) | E | E (nested) | L |
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| 104,608 | E (nested) | E | E | E | (kernel.return L) |
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| 104,610 | (kernel.return E) | L | L | L | C |
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| 104,611 | L | L | E | L | (kernel.return C) |
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| 104,613 | L | L | L | L | (next event) |
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| 104,617 | C | C (NtClose) | L | C | - |
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### Pattern classes
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- **Class jitter-1 (contended-then-nested)**: `E W E L L C`. 1/4 samples.
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- **Class jitter-2 / c21 (fast-path-then-nested)**: `E E L L C`. 2/4 samples.
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- **Class jitter-3 (upstream-drift, contended earlier)**: `E W E L E E L L C`. 1/4 samples.
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- **Class ours (fast-path, no nested cleanup)**: `E L C`. 1/1 sample.
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Canary's ALL 4 samples take the nested-Enter branch; the variability is
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only in *when* the slow-path (`W`) fires and on which SID. Ours never
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takes the nested-Enter branch — different guest control-flow.
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## SID overlap
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Of the 10 most-frequent wait.begin SIDs on tid=6 per cold:
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| SID | jitter-1 | jitter-2 | jitter-3 | cold-c21 |
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|----------------------|----------|----------|----------|----------|
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| `a25a16a4f6f547aa` | 19 | 27 | 11 | 28 |
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| `2a70efeeed4f4fb6` | 13 | 14 | 12 | 12 |
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| `72a4170012353517` | 9 | 13 | 9 | 10 |
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| `1938a086284cdbf1` | 1 | 1 | 1 | (likely 1) |
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| `cf2f57a69895b36c` | 1 | 1 | 1 | (likely 1) |
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| `648cb0d5adfa9125` | 1 | 1 | (absent) | (likely 1) |
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| `75ae880ec432eb36` | 1 | (absent) | (absent) | (absent) |
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| `3b234bbee19d74cf` | 33 | (absent) | (absent) | (absent) |
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| `b8e833ada16e15fa` | 31 | (absent) | (absent) | (absent) |
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| `8ec49cc7eb991db6` | (absent) | 33 | (absent) | 33 |
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| `d896adc3741c77c1` | (absent) | 31 | (absent) | (absent) |
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| `9eda93a619ebd4ca` | (absent) | (absent) | 34 | (absent) |
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| `84fe8d4c3a65f040` | (absent) | (absent) | 31 | (absent) |
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| `14afe71d37ff58a7` | (absent) | (absent) | (absent) | 31 |
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**Reading**:
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- A *stable core* exists: `a25a16a4f6f547aa`,
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`2a70efeeed4f4fb6`, `72a4170012353517` appear in all 4 cold samples
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with ±20% count variance.
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- A *swappable shell* exists: the top-2-SIDs by count are different
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per-cold. These are likely transient per-run pseudo-handles that
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canary's `XObject::GetNativeObject` assigns when wrapping CSes that
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happen to contend in this run.
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- `75ae880ec432eb36` (the original C+20 wedge SID) is *unique to
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jitter-1*. C+18/C+21 absorbers treat it as shared-global; the absorb
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was correct.
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## Bit-stability properties
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| dimension | bit-stable? | scope of variance |
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|---|---|---|
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| Total RtlEnterCS call count | YES (±1) | 19,517-19,519 across 4 |
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| Total RtlLeaveCS call count | YES (±2) | 19,517-19,519 across 4 |
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| Which idx contains a wait.begin in 104,595-104,620 | NO | varies among {104,603, 104,606, none} |
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| Which SIDs see wait.begin on tid=6 | NO | 3-7 SIDs differ per-cold |
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| Frequency-stable SID set | YES | 3 SIDs stable across 4 colds |
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| Idx 104,607 first-event-name after C+21 absorb | YES (within canary) | always `E` (nested-Enter) |
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| Idx 104,607 ours event name | YES | always `L` |
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| Nested-Enter taken? | YES on canary, YES NO on ours | structural divergence |
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## Implication for diff-tool absorber chain
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C+18 (handle.create shared-global SID), C+21 (wait.begin
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shared-global SID), and Phase D D-extension (nested-CS-cleanup
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absorber) together fold ALL 4 canary cold shapes into a single
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canonicalized form which then aligns with ours. The C+21 absorber
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in particular handles 0..3 wait.begin events per cold without
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affecting matched-prefix. **The empirical jitter profile is
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absorbed**; the cap that follows (105,046 = `VdInitializeEngines`)
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is an unrelated VD-subsystem class.
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## Predicted variance budget for further phases
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Based on these 4 cold samples:
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- Per-cold-shape wait.begin event count near a contention region:
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0-3 events (mean ~1.5). Diff-tool absorber capacity is ≥3 already.
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- Upstream index drift due to scheduling: ≤3 events. C+21 covers up
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to 1, D-extension's 32-pair cap covers far more.
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- SID identity drift: 3+ SIDs differ per cold, all absorbed by
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shared-global recipe.
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The absorber chain is over-provisioned relative to the empirically
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observed jitter range.
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