ADR housekeeping: category prefixes, lifecycle folders, retroactive 0034-0037
Filename + lifecycle:
- ADR rename to ADR-NNNN-<cat>-title.md with 8 3-letter category prefixes
(dev / mem / lat / prog / algo / par / api / ver). Numbers stay immutable.
- ADR Lifecycle split into 3 folders, documented in CLAUDE.md Part 2:
docs/adr/ (Accepted), docs/adr-proposed/ (Proposed/Stub/Draft),
docs/adr-history/ (Superseded/Merged). Status field gains "Draft" for
retroactive docs pending verification.
Merges (one ADR per topic, no change-history annotations):
- ADR-0017 absorbs ADR-0019 (Cube NOC + per-PE HBM connectivity, 10 D-items)
- ADR-0014 absorbs ADR-0021 (PE pipeline execution model, 8 D-items incl.
TileToken self-routing and multi-op composite epilogue scope)
- ADR-0023 absorbs docs/ipcq-dma-codesign-hw.md as new "HW Realization
Notes (Informative)" section (D16-D23 + Open HW Questions). codesign-hw.md
deleted; ADR-0019/0021 moved to adr-history with one-line stub status
Retroactive documentation (G4 closures, code-verified):
- ADR-0037 forwarding component (TransitComponent: first-flit overhead,
serial worker, path-based routing, single impl/multiple names)
- ADR-0036 IO_CPU component (target_start_ns global barrier stamping,
per-cube fan-out, response aggregation)
- ADR-0035 M_CPU & M_CPU.DMA component (3 fan-out paths, DMA Resources,
target_start_ns passthrough)
- ADR-0034 HBM controller internal design (per-PC state, address-based
selection, flit-aware per-flit commit, async finalize, command-only
fallback path)
Content updates:
- ADR-0010 expanded to full CLI surface (run/probe/web), retitled
"Command Line Interface and Execution Semantics"
- ADR-0007 D2 rewritten to current state; ADR-0015 supersession notes pruned
- ADR-0005 wrapped in Decision header with D1-D5; ADR-0022 metadata
block replaced with standard Status header
- ADR-0024 trimmed to rank=SIP launcher essentials (D1-D4);
ADR-0027 cleaned of supersession history
- ADR-0033 D6 cleanup: address-based PC selection moved out of future-work
(now documented in ADR-0034 D3); related D1/D3 wording realigned
- Cross-references back-filled in 5 ADRs (G3 gaps closed)
Onboarding docs split:
- docs/onboarding/ created
- moved: hw-architecture-overview.md, latency-model.md, di-presentation.md,
ccl-author-guide{,.en}.md
- references updated in README, ADR-0023{,.en}, src/kernbench/ccl/__init__.py
Source / test / yaml: ADR-NNNN cross-references in docstrings and YAML
comments updated after the merges (ADR-0021->0014 D6, ADR-0019->0017 D8).
No behavior change.
Tooling:
- tools/verify_adr_lang_pairs.py + tests/test_verify_adr_lang_pairs.py
(ADR EN/KO pair invariant checker)
- .claude/commands/report.md tracked (/report slash command)
- .gitignore: allow .claude/commands/*.md while keeping settings files ignored
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
@@ -0,0 +1,200 @@
|
||||
# ADR-0037: Forwarding Component (forwarding_v1)
|
||||
|
||||
## Status
|
||||
|
||||
Accepted
|
||||
|
||||
## Context
|
||||
|
||||
The simulation graph has many node positions that exist purely to model
|
||||
fabric traversal — NOC mesh routers, switches, UCIe protocol endpoints,
|
||||
IO chiplet io_noc, transit cubes. These share a common pattern: receive
|
||||
a message, apply per-component overhead (modeling header decode +
|
||||
routing decision time), forward to the next hop along the pre-computed
|
||||
path.
|
||||
|
||||
This ADR defines the contract for these transit nodes: a single
|
||||
component type (`TransitComponent`) that handles flit-aware forwarding
|
||||
with wormhole cut-through semantics, used under multiple impl names
|
||||
according to the conceptual role each instance plays.
|
||||
|
||||
## Decision
|
||||
|
||||
### D1. Role
|
||||
|
||||
The Forwarding component (`TransitComponent` class) is a **stateless
|
||||
transit node** in the simulation graph. It models any fabric position
|
||||
where a message physically traverses but no semantic processing
|
||||
happens.
|
||||
|
||||
Per traversal, the component:
|
||||
|
||||
1. Reads an incoming Transaction or Flit from an `in_port`.
|
||||
2. Applies the configured per-component overhead (`overhead_ns`),
|
||||
applied **once per Transaction** even across multi-flit payloads
|
||||
(see D2).
|
||||
3. Looks up the next hop along the Transaction's pre-computed `path`.
|
||||
4. Forwards to the corresponding `out_port`; at the terminal node
|
||||
(no next hop), signals `txn.done` once the `is_last` flit arrives.
|
||||
|
||||
The component **does NOT**:
|
||||
|
||||
- Decide routing — paths are pre-computed by the router (ADR-0002 /
|
||||
ADR-0017 D2). Forwarding only executes the per-hop step.
|
||||
- Model wire propagation or bandwidth occupancy — separate wire
|
||||
processes between components handle that (ADR-0015 D2).
|
||||
- Resolve addresses — the AddressResolver does that (ADR-0017 D9).
|
||||
- Aggregate completion — terminal endpoints (IO_CPU, M_CPU, HBM_CTRL)
|
||||
handle that.
|
||||
|
||||
### D2. First-flit overhead model (header decode)
|
||||
|
||||
Per-Transaction `overhead_ns` is applied **exactly once**, at first
|
||||
flit arrival:
|
||||
|
||||
- `_txn_decoded: set[int]` tracks which Transactions have already
|
||||
paid the overhead at this node.
|
||||
- On first-flit arrival for a Transaction: `yield self.run(env,
|
||||
msg.txn.nbytes)` — pays the overhead.
|
||||
- Subsequent flits of the same Transaction skip the overhead — they
|
||||
pipeline through with no extra delay.
|
||||
- On `is_last` flit: remove the Transaction from `_txn_decoded`.
|
||||
|
||||
This models the real-HW behavior where header decode and routing
|
||||
decision happen once on first flit; payload flits then stream through
|
||||
the same path (wormhole cut-through). Multi-hop pipelining emerges
|
||||
naturally — each hop adds its own first-flit overhead, but flits
|
||||
after the first do not re-pay overhead at any hop they have already
|
||||
passed first.
|
||||
|
||||
### D3. Serial worker forwarding (preserves order)
|
||||
|
||||
The component's worker is a single SimPy process that consumes flits
|
||||
from `_inbox` and forwards them serially in arrival order. The
|
||||
component does NOT spawn `env.process(...)` per flit.
|
||||
|
||||
Rationale: if the first flit yields on `overhead_ns` while subsequent
|
||||
flits run in parallel processes, the later flits can overtake the
|
||||
first. This produces out-of-order delivery and lets the `is_last`
|
||||
flit arrive at the destination before the first flit — corrupting
|
||||
both the transaction's completion semantics and any flit-index-based
|
||||
processing downstream.
|
||||
|
||||
### D4. Path-based next-hop routing
|
||||
|
||||
Routing is **not** a Forwarding-component concern. The Transaction
|
||||
arrives with a pre-computed `path` (built by the router; ADR-0002 /
|
||||
ADR-0017 D2). The component just looks up its own position in the
|
||||
path and forwards to `path[index + 1]`:
|
||||
|
||||
```python
|
||||
def _next_hop_in_path(self, txn):
|
||||
my_id = self.node.id
|
||||
path = txn.path
|
||||
for i, n in enumerate(path):
|
||||
if n == my_id and i + 1 < len(path):
|
||||
return path[i + 1]
|
||||
return None
|
||||
```
|
||||
|
||||
If `next_hop` is found and present in `out_ports`, the flit is
|
||||
forwarded. Otherwise (terminal node), `txn.done.succeed()` is
|
||||
invoked when the `is_last` flit arrives.
|
||||
|
||||
### D5. Flit-aware mode with Non-Flit fallback
|
||||
|
||||
`_FLIT_AWARE = True` opts this component out of the base class's
|
||||
flit-reassembly logic in `_fan_in`. Flits are placed directly on
|
||||
`_inbox` (no reassembly), enabling per-flit handling in the worker
|
||||
loop (D2, D3).
|
||||
|
||||
Non-Flit messages — zero-byte control Transactions and other
|
||||
non-chunkified payloads — fall through to the base class's legacy
|
||||
`_forward_txn` path via `env.process`. This preserves backward
|
||||
compatibility for control-plane traffic that does not benefit from
|
||||
flit-level processing.
|
||||
|
||||
### D6. Multi-stream merging at the base class
|
||||
|
||||
Multi-stream FIFO merging at routers is the base class's
|
||||
responsibility, not Forwarding's. The base class's `_fan_in` spawns
|
||||
one process per `in_port`; all push to a single shared `_inbox`.
|
||||
Flits from different upstream streams therefore interleave at
|
||||
flit granularity in `_inbox`'s FIFO order.
|
||||
|
||||
The Forwarding worker simply consumes `_inbox` in arrival order —
|
||||
correctly modeling per-router multi-flow arbitration as
|
||||
fair-FIFO over the shared inbox.
|
||||
|
||||
### D7. Single implementation under multiple impl names
|
||||
|
||||
A single `TransitComponent` class is registered under four impl names
|
||||
in `components.yaml`:
|
||||
|
||||
- `builtin.forwarding` — generic forwarding (e.g., `io_noc`,
|
||||
`noc_router`, UCIe conn bridges)
|
||||
- `builtin.switch` — tray-level switch
|
||||
- `builtin.noc` — cube-level NOC fabric (legacy singleton; current
|
||||
NOC routers use `builtin.forwarding`)
|
||||
- `builtin.ucie` — UCIe protocol endpoint
|
||||
|
||||
All four aliases instantiate the same class with the same behavior.
|
||||
Per-instance differentiation lives only in `attrs.overhead_ns`.
|
||||
Separate impl names exist as intent tags for readability and to
|
||||
allow future divergence without backward-incompatible config
|
||||
changes.
|
||||
|
||||
### D8. Configurable `overhead_ns`
|
||||
|
||||
A single attribute drives per-instance latency:
|
||||
|
||||
| Usage site | impl name | overhead_ns |
|
||||
| --- | --- | --- |
|
||||
| Tray-level switch | `builtin.switch` | 5.0 |
|
||||
| Cube NOC router | `builtin.forwarding` | 2.0 |
|
||||
| IO chiplet io_noc | `builtin.forwarding` | 0.0 |
|
||||
| UCIe protocol endpoint (`ucie-{N,S,E,W}`) | `builtin.ucie` | 8.0 |
|
||||
| UCIe conn bridge (`ucie-{PORT}.conn{N}`) | `builtin.forwarding` | 0.0 |
|
||||
|
||||
Default is 0.0. The attribute is read at each `run()` invocation, so
|
||||
dynamic reconfiguration is possible but not currently used.
|
||||
|
||||
## Consequences
|
||||
|
||||
### Positive
|
||||
|
||||
- A single class handles all transit-node roles in the simulation
|
||||
graph — minimal code surface for a high-population component type.
|
||||
- Flit-aware processing + serial worker preserves wormhole semantics
|
||||
across multi-hop paths without per-flit process overhead.
|
||||
- `overhead_ns` is the only per-instance tunable; routing, BW, and
|
||||
address resolution stay cleanly separated in their own components /
|
||||
modules.
|
||||
- Multi-stream merging emerges from the base-class structure; no
|
||||
router-specific logic duplicates fair-FIFO arbitration.
|
||||
- Non-Flit fallback path keeps control-plane traffic working without
|
||||
forcing every message into the flit framework.
|
||||
|
||||
### Negative
|
||||
|
||||
- The single class hides usage-site intent inside `attrs.overhead_ns`
|
||||
configuration; readers must consult `topology.yaml` +
|
||||
`components.yaml` to see which impl name maps to which behavior
|
||||
class.
|
||||
- Per-flit serial worker is a bottleneck if `overhead_ns` is large
|
||||
and many concurrent transactions arrive at the same router; current
|
||||
values (0–8 ns) make this negligible.
|
||||
|
||||
## Links
|
||||
|
||||
- ADR-0002 (Routing distance — path computation)
|
||||
- ADR-0015 D1 (Component port model)
|
||||
- ADR-0015 D2 (Wire process — BW + propagation, separate from this
|
||||
component)
|
||||
- ADR-0015 D6 (Transit cube forwarding pattern)
|
||||
- ADR-0016 D1 (IO chiplet io_noc — uses this component)
|
||||
- ADR-0017 D1 (Cube NOC routers — use this component)
|
||||
- ADR-0017 D6 (UCIe decomposition — `ucie-{PORT}` instances use this
|
||||
component)
|
||||
- ADR-0033 D1 (Flit-aware pass-through, first-flit overhead,
|
||||
multi-stream merge semantics)
|
||||
Reference in New Issue
Block a user