NiccoloN
034c197260
Validate Operations / validate-operations (push) Failing after 3h10m55s
add plot generation scripts adjust validation tools add up-to-date results
102 lines
5.8 KiB
Markdown
102 lines
5.8 KiB
Markdown
# Spatial scheduling
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`ScheduleAndRealizeSpatial` constructs a shared `ComputeGraph`, then selects
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latency PEFT or pipeline scheduling. Pipeline mode does not run PEFT.
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See [implementation notes](scheduling-implementation.md) for fragment-view eligibility,
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receive forwarding, transfer rounding, cost-model boundaries, and recovery limits.
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## Ownership
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| Responsibility | Owner |
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| Instances, dependencies, execution/transfer costs, resident weights | `ComputeGraph`, `ComputeInstanceUtils` |
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| Target resources and physical link costs | Compiler target adapter via `SchedulingTarget` |
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| Latency priorities, reservations, placement, per-core order | `PeftScheduler` |
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| Capacity-driven workload splitting | `PipelineWorkloadPreparation` |
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| Groups, stage partitioning, core budgets | `buildPipelineGroups`, `partitionPipelineGroups`, `assignPipelineStages` |
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| Topology clustering and stage-local packing | `PipelineCoreLayout`, `packPipelineStages`, `IndexedResidentWeights` |
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| Timing evaluation and publication equivalence | `evaluateSchedule`, `populateScheduleEquivalenceClasses` |
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| Selected execution order and homogeneous runs | Scheduled compute planning/materialization |
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| Routing, forwarding, blocking communication order | Deferred transfer planning and communication scheduling |
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| READY/FREE counts, registers, overwrite/restart boundaries | Deferred boundary planning/realization |
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Both strategies produce `MergeScheduleResult`: core assignments, contiguous
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per-core slots, estimated starts, last-task markers, equivalence classes, and
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cost summaries. Pipeline results also assign each core a stage. Materialization
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uses verified slots for execution order and merges only consecutive compatible
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instances. Graph/class lane identity does not imply core identity or execution
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order.
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Dependencies and transfer costs share `getGraphBatchPublicationMap`.
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Statically proven physical-slot projections support many-to-many edges;
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unproven projections retain complete producer dependencies, including region
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captures. Malformed publication metadata fails graph construction.
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Normative contracts:
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[graph fragments](../../.agents/invariants/GRAPH_COMPUTE_BATCH_INVARIANT.md),
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[pipeline stages](../../.agents/invariants/PIPELINE_SCHEDULING_INVARIANT.md),
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[target boundary](../../.agents/invariants/SPATIAL_TARGET_GENERALITY_INVARIANT.md),
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[synchronization](../../.agents/invariants/PIM_SYNCHRONIZATION_INVARIANT.md),
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and [performance](../../.agents/invariants/PERFORMANCE_OPTIMIZATION_INVARIANT.md).
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## Costs and interpretation
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Execution and fixed transfer costs use integer nanoseconds, converted from
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target cycles. Bytes, elements, flits, weight slots, and lanes remain resource
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quantities. Memory work is rounded at its actual fragment/run granularity;
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runtime-free views cost zero. Transposes charge memory traffic and strided
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vector work; concatenation charges per-input blocks per outer row. Direct
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receives into assembly storage avoid duplicate endpoint-memory charges.
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Sub-byte storage is analyzable in Spatial but rejected by byte-addressed PIM
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communication lowering.
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The evaluator separates serial work, per-core work, dependency critical path,
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summed transfer work, single-inference completion, and stage spans. Dependency
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paths exclude core-order constraints; completion includes them. Stage spans
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exclude cross-stage routing, restart/host synchronization, and contention.
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Simulator latency and measured throughput remain the performance gates.
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Pipeline partitioning uses ordered-packing/dependency-tail priorities and
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nominal movement volumes. PEFT and final evaluation use physical cost estimates.
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Placement ranks maximum per-core compute/incident-transfer demand, then stage
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completion and compute load; within 1% demand, stage span breaks the tie.
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These are placement heuristics, not a steady-state timing model.
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## Capacity and recovery
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Distinct-weight union / per-core capacity is a lower bound; an oversized task
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is infeasible. Ordered pack counts estimate budgets, and failed heuristic
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packing does not prove infeasibility. Exhausted budgets restart from lower
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bounds and constructive packing establishes feasibility.
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Latency reservations try load/communication-aware placement, then
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largest-weight-first and shared reuse-first best fit on failure. Pipeline
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packing compares arrival/load-aware candidates and uses constructive recovery.
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The shared constructor retries in reverse order, then at most 16 single-choice
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deviations within 65,536 core-candidate checks. Successful placements are
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preserved. Exhausted search produces a bounded diagnostic, not a claim of
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proved hardware infeasibility.
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## Complexity and limits
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Let `T` be tasks, `E` dependencies, `P` cores, `G` groups, `S` stages,
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`R` weight references, `W` distinct weights, and `C` modeled work.
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| Analysis | Time / storage |
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|---|---|
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| Schedule evaluation | `O((T + E) log T + P)` / `O(T + E + P)` |
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| Weight indexing | Up to `O(R W)` equality comparisons |
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| Weight lower bounds | `O(R + W)` / `O(W)` bits |
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| Constructive best fit | `O(T log T + P R + P W)` / `O(P W)` bits plus `O(T + P)`; bounded retries only on failure |
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| Partition DP | Up to `O(S G² ((T + R) log C + W))` plus dependency traversal / `O(S G²)` cache |
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| Topology clustering / cached PEFT distances | `O(P²)` time |
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| Concat cost extraction | `O(A D)` for `A` inputs of rank `D`; constant auxiliary space |
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| Cached pipeline priorities | `O(T + D)` time / `O(T + G)` space for `D` template-body operations |
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| Exact projections | `O(Q + L)` time/temporary space for `Q` slot visits and `L` producer lanes; publication maps cached |
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| Conservative producer tracing | Linear in the input projection DAG, including captures |
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Latency insertion-gap searches can remain quadratic. Issue overhead,
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eliminated assembly copies, contention, and pipeline synchronization remain
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cost approximations. Changes require matched execution measurements.
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