Roofline¶

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This document describes the roofline field in src/tileops/manifest/: what it is, how to author one, and who consumes it.

1. Performance Model¶

1.1 Baseline Selection¶

Kernel performance is measured against hardware Speed-of-Light (SOL), not against PyTorch or vendor baselines. The roofline field supplies the per-op inputs this model needs (§2).

1.2 Metric Definition¶

memory_time  = bytes_moved / hbm_bandwidth
compute_time = total_flops / peak_flops
sol_time     = max(memory_time, compute_time)
efficiency   = sol_time / actual_time

Inputs:

bytes_moved, total_flops — manifest roofline (§2).
hbm_bandwidth, peak_flops — GPU profile (§5.1).
actual_time — benchmark output (§5.2).

Bound type is whichever term dominates sol_time (memory-bound if memory_time > compute_time, else compute-bound). It depends on shape, not on the op; the roofline tool computes it per-workload and the manifest does not declare it.

1.3 Convention¶

Per-element FLOP rule for elementwise ops:

One basic arithmetic op (add, sub, mul, div, neg, abs, recip) counts as 1 FLOP.
One transcendental call (exp, log, log1p, erf, tanh, sin, cos, sqrt, rsqrt, etc.) counts as 1 FLOP at the convention level. Hardware-specific cost models do not feed back into the manifest.
One compare-and-select (max, min, maximum, minimum, single- or two-bound clamp, relu-style branch, where) counts as 1 FLOP per output element.
Predicate-only outputs (eq, gt, etc.) count as 1 FLOP per element.

Composite ops sum their primitives — sigmoid = neg + exp + add + recip = 4 FLOPs/elem; silu = sigmoid + mul = 5 FLOPs/elem.

2. Field Specification¶

2.1 Output Contract¶

Per workload, the roofline field yields (flops: int, bytes: int). Consumers read these integers via op.eval_roofline() on an instantiated Op (§4.4).

2.2 Formula Modes¶

An entry uses one of two modes:

Mode	Form	When
Inline	`vars?` + `flops`/`bytes`	Formula fits a Python expression.
Func	`func: "module.path"`	Formula needs real Python logic.

Inline. Roofline variables come from shape dim names where possible. Anything shape cannot supply — arbitrary-rank dims, slice products, shape-derived quantities — is declared in vars. flops and bytes are Python expressions over all resolved variables + elem_bytes + approved helpers (§4.4.4). elem_bytes is the byte size of the first input's dtype. Ops whose bytes depend on multiple input dtypes (mixed-precision GEMM, Attention, etc.) cannot be expressed in inline mode and must use func.

Func. Point at tileops.perf.formulas.<name>. The callable is human-authored and returns (flops, bytes). Recommended signature: func(op) — matching the agent-generated eval_roofline(self) path, which is what codegen's emitted call assumes. A human author who prefers a different signature owns the resulting integration (e.g., a wrapper). Use func when inline arithmetic is insufficient (mixed-precision byte accounting, conditionals, shape traversal, data-dependent logic).

# Inline — shape dim names cover all variables
roofline:
  flops: "2 * M * N * K"
  bytes: "(M * K + K * N + M * N) * elem_bytes"

# Inline — shape cannot supply the variables; vars fills in
roofline:
  vars:
    M: "product(x.shape[:dim])"
    N: "x.shape[dim]"
  flops: "4 * M * N"
  bytes: "(2 * M * N + N) * elem_bytes"

# Func — complex formulas
roofline:
  func: "tileops.perf.formulas.my_op_roofline"

3. Consumers¶

src/tileops/manifest/ is the source of truth for the roofline field. Four modules read it:

Schema validator / CI — structural checks only (schema, mode exclusivity, func importability). Does not execute formulas or hold a helper whitelist. Spec: §4.1.
Benchmark layer — instantiates an Op per workload and reads (flops, bytes) from op.eval_roofline(). Hardcoded formulas in benchmark files are a CI failure. Spec: §4.2.
Roofline tool (M5) — reads (flops, bytes) from benchmark output (which was produced by op.eval_roofline()), combines with GPU profile (§5.1) to compute SOL efficiency and bound type. Spec: §4.3.
Op codegen — generates each op's eval_roofline() method; is the authoritative gate for name and form correctness. Spec: §4.4.

Tests and workloads are not consumers: they may supply shapes and dtypes but must not define or reinterpret roofline formulas.

4. Consumer Specifications¶

4.1 Schema Validator / CI¶

Runs on every PR touching src/tileops/manifest/. Scope is structural.

Every roofline entry MUST satisfy:

Required fields per mode: inline has flops and bytes; func has func.
Mode exclusivity: flops/bytes/vars and func do not coexist.
Field types: flops/bytes/func are non-empty strings; vars is a mapping of str → non-empty str.
func dotted path resolves at import time.

The validator enforces these rules.

Out of the validator's scope:

Name whitelist — a formula's names are checked by codegen (§4.4), which owns the binding table. Validator does not mirror it.
Form checks (layer violations, forbidden AST nodes) — codegen refuses to emit invalid forms.
Numeric checks (finite / non-negative / numeric) — tests exercise generated eval_roofline() on each workload.

Validator holds no callables, no sample bindings, no __builtins__ sandbox. Adding a helper does not touch the validator.

4.2 Benchmark Layer¶

Contract:

Instantiate the Op for each workload and call op.eval_roofline() to obtain (flops, bytes). No manifest-level helper exists — roofline evaluation lives only inside each Op's generated method.
ManifestBenchmark and workloads_to_params(..., include_extra=True) are the canonical consumers; non-reserved workload keys forward as op-call params passed to the Op's __init__.
A benchmark file that computes FLOPs or bytes locally is a CI failure.
Benchmark output must record the (flops, bytes) returned by op.eval_roofline() so downstream consumers (M5) can read the numbers without re-instantiating ops.

4.3 Roofline Tool (M5)¶

Inputs:

Benchmark output (JSON/CSV) produced by M4, carrying per-workload latency and the (flops, bytes) that benchmark obtained from op.eval_roofline().
GPU profile (§5.1).

Outputs: SOL efficiency, bound type, per-workload reports.

Does not interpret formula strings at all. M5 reads pre-computed numbers from the benchmark output; it never instantiates Ops or runs roofline expressions.

4.4 Op Codegen¶

Codegen runs for status: implemented entries only. spec-only entries — where either the implementation does not exist or the Op interface does not yet match the manifest — are skipped; codegen re-evaluates them once the status flips.

Codegen is the authoritative gate for name and form correctness. A formula referencing an unknown name or violating a layer's form constraints fails codegen; a manifest that fails codegen cannot land. Numeric correctness is exercised by tests, not codegen.

4.4.1 Method Template¶

For each op, codegen emits an eval_roofline() method returning (flops: int, bytes: int). The method signature is part of the shared Op interface defined in ops-design-reference.md; this document specifies only how the body is generated from the manifest.

def eval_roofline(self) -> tuple[int, int]:
    M = self.M
    N = self.N
    elem_bytes = self.dtype.itemsize
    return (
        4 * M * N,
        (2 * M * N + N) * elem_bytes,
    )

4.4.2 Manifest Inputs¶

For each manifest entry, codegen reads one of:

Inline — vars (optional), flops, bytes. All are Python expression source strings. Codegen emits the method body per §4.4.3.
Func — func (dotted module path resolving to a human-authored callable). Codegen emits return <func>(self) as the method body. This presumes the recommended signature func(op) -> tuple[int, int] (returning (flops, bytes)), aligned with the agent-generated eval_roofline(self) shape. The recommendation is a reference for authors, not a gate — codegen does not introspect or validate the callable. If the author wants a different signature, they take responsibility for making the callable work with the emitted call (e.g., by writing a thin wrapper at the dotted path).

4.4.3 Expression Layers¶

Inline mode has two layers. Codegen emits them as two sequential blocks in the method body.

vars layer — shape-derived resolution. Allowed operations: tensor shape access, slicing, product(), range(), small comprehensions.
arithmetic layer — flops and bytes over resolved variables + elem_bytes + approved helpers only. Forbidden: tensor access, shape slicing, comprehensions, attributes, arbitrary calls.

Codegen actions emit two sequential blocks:

Block 1 — vars resolution.

Bind each signature.inputs tensor and signature.params name referenced by the roofline expressions to a local. Names declared in the manifest but unused by the roofline are not bound; ops are not required to expose them. Op-author conventions for exposing referenced names on the op instance are specified in .claude/domain-rules/ops-design.md.
Bind elem_bytes from whichever dtype source exists at the call site (§4.4.5): use self.dtype.itemsize when eval_roofline() runs at __init__ (fixed-rank — no tensor yet), and self.<first_input>.dtype.itemsize when it runs in forward() (arbitrary-rank — the tensor is bound).
If vars: is present, emit one assignment per entry in YAML declaration order: <name> = <vars[name]>, copying the expression string verbatim. Later entries may reference earlier locals.
If vars: is absent and shape is fixed-rank, emit assignments from the shape declaration (tuple-unpack self.x.shape, or read self.<dim> if the Op stored dims at __init__).

Block 2 — arithmetic. Return (<flops>, <bytes>) with both expression strings copied verbatim. They reference only Block 1 locals + elem_bytes + arithmetic-layer helpers (§4.4.4).

Do not inline a vars expression into the arithmetic expression (e.g. return (4 * product(x.shape[:dim]) * x.shape[dim], ...)). That collapses the two layers and violates arithmetic-layer restrictions.

Reduction dim handling in the vars layer follows the manifest shape_rules contract: validate range → normalize % x.ndim → reject duplicate axes for sequence dims. A roofline expression must not silently normalize an invalid axis.

Example — arbitrary-rank (explicit vars):

def eval_roofline(self) -> tuple[int, int]:
    # Block 1: vars layer
    x = self.x
    dim = self.dim
    elem_bytes = self.x.dtype.itemsize
    M = product(x.shape[:dim])
    N = x.shape[dim]
    # Block 2: arithmetic layer
    return (
        4 * M * N,
        (2 * M * N + N) * elem_bytes,
    )

Fixed-rank form: see the template in §4.4.1.

Any Name node not resolvable to a Block 1 local, elem_bytes, or an arithmetic-layer helper causes codegen to raise. Any forbidden AST node (Attribute, Subscript, Comprehension, Lambda, …) in the arithmetic layer also causes codegen to raise. These are the enforcement of the "authoritative gate" responsibility.

4.4.4 Namespace¶

Codegen knows how to bind the following names when generating the method body. This is the single source of truth for what an inline formula may reference.

vars layer

Bucket	Names
Tensors	All `signature.inputs` names, exposed with a `.shape` accessor
Params	All `signature.params` names
Constants	`elem_bytes`
Helpers	`product`, `isinstance`, `len`, `set`, `tuple`, `list`, `range`, `int`, `float`, `bool`, `min`, `max`, `sum`, `abs`, `log2`, `ceil`, `floor`

arithmetic layer

Bucket	Names
Variables	Resolved vars from the vars layer
Constants	`elem_bytes`
Helpers	`ceil`, `floor`, `log2`

Adding or removing a helper = edit codegen's binding table. No parallel update in validator or anywhere else is required. If a formula references a name not in this table, codegen fails; the manifest does not land.

4.4.5 Runtime Timing¶

Generated eval_roofline() follows shape-inference timing: resolve variables at the first moment they are known, cache the result, do not recompute for identical inputs.

Op category	Variables known at	`eval_roofline()` behavior
Fixed-rank	`__init__` (all dimensions provided)	Called once during init; result may be stored on the Op.
Arbitrary-rank	`__init__` for `static_dims`; `forward` for remaining dynamic dims	Called in `forward()` when dynamic vars are resolved; cache by input.

Non-runtime consumers must instantiate the Op (or read pre-computed (flops, bytes) from benchmark output). No manifest-level roofline evaluator exists; every value flows through op.eval_roofline().

4.4.6 Evaluator Surface Boundary¶

Roofline expressions live in exactly one place at runtime: the plain Python body that codegen emits into each op's eval_roofline(). No standalone roofline evaluator exists.

Surface	Scope	Interprets roofline expressions?
Op-local AST evaluator	—	REJECTED — must not be built
Manifest-level roofline evaluator	—	REJECTED — must not be built

Rules:

No tileops.manifest.eval_roofline() / resolve_roofline_vars() helper that evaluates roofline expressions exists in the target design. Any consumer wanting (flops, bytes) either calls op.eval_roofline() on an Op instance or reads pre-computed values from benchmark output.
Generated eval_roofline() must not parse, AST-analyze, or safe-eval its own formula strings. Codegen does the name/form check at generation time (§4.4.3 / §4.4.4) and then copies validated expressions into plain Python.
If a formula is too complex for inline arithmetic (conditionals, shape traversal, data-dependent logic), switch the entry to func mode (§2.2). Do not extend inline formulas into a mini-language.

5. Reference¶

5.1 GPU Profile¶

Hardware parameters use theoretical values with calibration factors from one-time microbenchmark measurements. YAML files store only theoretical and calibration; effective = theoretical × calibration is computed by load_profile():

# src/tileops/perf/profiles/<gpu>.yaml
hbm:
  theoretical: 4800e9       # bytes/s, from spec sheet
  calibration: 0.848        # from microbench (STREAM Triad)
tensor_core:
  fp16:
    theoretical: 989.5e12   # FLOPS, from spec sheet
    calibration: 0.75       # from microbench (cuBLAS peak)

Profiles are stored in src/tileops/perf/profiles/. Microbenchmarks for calibration live in benchmarks/hardware/.

5.2 Benchmark–Roofline Decoupling¶

Benchmark (M4) produces per-workload records containing raw time and the (flops, bytes) from op.eval_roofline(). Roofline (M5) is a separate tool that reads those records + GPU profile to compute efficiency. This separation enables:

Re-analyzing historical data when GPU profiles are updated
Multiple consumers of raw benchmark data (roofline, regression detection, dashboards)
Benchmark module has no third-party dependencies beyond the project itself