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71 lines
5.0 KiB
Markdown
71 lines
5.0 KiB
Markdown
# Package ra — the wait rule, present credit, server-owned `gPipeInputs` (P5e; parallel, lands last)
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Read in this order, all of it: `PACKAGE-PREAMBLE-P5E.md`, `INTEGRATOR-DECISIONS-P5E.md` (ID-83,
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ID-84, ID-91, ID-92, ID-93 are yours), `BRIEF-P5E.md` (§0, §1, §2 "ra", §3 the integration gate, §4
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the device exit, §6 rulings 3, 4, 13, 14, 15, 17, 18), `CONTRACT-P5E.md` §2 and §3 (all of both),
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your scout report `scout-S6.md` (all of it), and lists (b) and (c) of `kimi-audit.md`. Notes:
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`//wsl.localhost/Arch/home/swung/w7/notes/p5e/`.
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Your slug is `ra`; your tree is `~/w7/p5e-ra` (branch `p5e/ra`, based on the landed c0e head — NOT
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on the family packages; you are parallel to them and rebase at landing). c0e landed the `WaitClass`
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column, `MGPipeWaitClassFor(op)`, the `RunAhead` / `PresentCredit` knobs, `kCapRunAheadApply` (bit
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10) and `kMGPipeP5eRunAheadReady = false`; id landed the `CurrentRecordBarriered` line in `ApplyOne`.
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## What "done" means
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The mechanism exists and is INERT until the integration commit: with `kMGPipeP5eRunAheadReady`
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false the server never publishes bit 10, the client never arms run-ahead, and every gate is exactly
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as green as today. Your last commit flips that constant — but only after the family packages have
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landed and the integrator says so, so structure your branch that way (the flip is its own final
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commit, trivially revertable).
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1. **The predicate.** `MGPipeBarriered(op, payload, applierState)` (c0e declared it) computed
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identically by both roles: the static `WaitClass` column, plus XFB-active from the context values
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and the `kDrawClientArrays` flag (ruling 3 / ID-83). The server's `ApplyOne` already sets
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`CurrentRecordBarriered` from it (id's line).
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2. **The client wait rule.** `EmitAndWaitTails` after `PublishAndNotify`: reply rows wait; barriered
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rows wait; unbarriered rows return. Present pacing through `WaitForPresentAck` with credit
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(default 1, range 1..8; ID-92) — the plumbing exists end to end and has no production caller
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today; `MGPPresent::FrameSerial` minted client-side; `OnPresent` returns the credit. Drains and
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forced waits per contract §2.5 (MapBuffer / GetBufferSubData / glFinish / fence client-wait /
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the EGL forwarders / the glGetError window — name the relaxation in the contract and in code).
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3. **`resource_subdata`'s buffer half stops waiting** (ruling 15 / ID-93): the reply Bool is
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discarded at the call site today, so every 64 KB persistent-map block push is a hidden round
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trip. The row keeps its `kReplySlot` on the wire; the client neither waits nor reads. The texture
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half keeps its reply (trailing).
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4. **`gPipeInputs` becomes server-role memory for unbarriered records** (contract §3): the client's
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residual fill and its stamp bookkeeping do not run for them (the tracker walk and the emitters
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still run — they produce records); the stamp becomes server-private; `MGPipeInputUnfreshRead`
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becomes an UNCONDITIONAL detector for unbarriered applies (a named Fatal, not a counter), which
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is what turns the strict lane into a hard gate. Barriered records keep P5C's semantics exactly
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(ID-84 / ruling 4).
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5. **Event-ring flow control** (contract §2.6): the ring's overflow is a Fatal today on the premise
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that the client drains at every verb — under run-ahead that premise is gone. Make the producer
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block/flow-control instead, and keep a named refusal for the impossible case.
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6. **Lifetime under run-ahead** (contract §2.7): slot reuse vs records in flight, `object_death`
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ordering, the deferred-destroy queue (ID-91 / ruling 13: it stays; an unbarriered enqueue is a
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finding — pin it), `Forget()` of a persistent map while its pushes are in SEG_STAGE.
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7. **The strict lane** (`.github/workflows/test.yml`): rewritten as a hard green gate with the
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contract §7 allowlist (`<field>@<verb>` for the barriered rows that keep pulling).
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8. Docs: `docs/Disaggregated/ARCHITECTURE.md` §11, §14, §17 — the wait rule, the credit, the event
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ring, `gPipeInputs` ownership.
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## Red-once (execute, revert, quote)
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1. Encode present without `WaitForPresentAck` → the credit-1 client behind a stalled apply thread
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publishes a third present; `Waits()` unchanged → red by count.
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2. Leave one `CopyField` in an unbarriered fill → `Fatal{RoleViolation, "gPipeInputs"}` by name.
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3. Count instead of Fatal under an unbarriered record → the strict lane turns red on the first
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pulled row (that is the gate's own red-once).
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4. Keep the event-ring Fatal → a unit case publishing ~300 KiB of events behind an unwaited
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sequence aborts; with flow control it completes.
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5. Publish bit 10 for Magma → `MagmaPipeIdentityTest` red.
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6. `MOBILEGL_IPC_RUN_AHEAD=0` renders identically; `MOBILEGL_IPC_VERB_BARRIER=0` under run-ahead is
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the documented red.
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## Gate (before the flip)
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`build`, `unit`, `isplit`, `gens`, `strict` — all exactly as green as the base, because every branch
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is inert with the bit unpublished. Your report must state, per numbered item above, what is wired
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and what it does when the bit flips; the integrator runs the device exit.
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