ADR 0004 — The Resource Manager allocates; the DFA compiler schedules

Accepted · 2026-05-21 · cortex/docs/adr/0004-rm-allocates-dfa-compiler-schedules.md

Status: Accepted Date: 2026-05-21 Source: docs/plan/bootstrap-plan.md, judgment call #4 (correction recorded there); docs/arch/cortex-repo.md, The All-Knowing Resource Manager Related: ADR-0008, ADR-0009

Context

The KPU is a spatial dataflow fabric. Tensors are physically distributed across the compute tiles, and their shape and location are part of how the KPU computes (“computational spacetime”). Time-slicing the fabric between operators would destroy the latency and energy efficiency that are its reason to exist.

Early drafts put “computational-spacetime scheduling” inside the Rust Resource Manager (RM). That was wrong.

Decision

Split the responsibilities cleanly:

• The DFA graph compiler (offline, separate repo) schedules. It fuses subgraphs and emits domain flow programs: scheduled, placed entities whose spacetime footprint is fixed at compile time.
• The Rust RM (core/) manages allocations: the live map of which domain flow programs occupy which physical tiles and memory regions, conflict detection, and release on completion.
• The KPU runs a loaded domain flow program’s dataflow itself. The host does no runtime scheduling.

Consequences

• No scheduler, fusion, or tile-placement logic belongs in core/. A feature that sounds like scheduling belongs in the compiler.
• Use the term “domain flow programs” (never “streamer programs”) for the compiler’s output.
• The RM’s state is small (an allocation map), which is what makes crash-only recovery feasible (ADR-0009).
• Current state: the RM lifecycle and memory-provider HAL exist; the allocation arbiter is issue #23.