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kernbench2/tests/analytical_visualization/test_chip_roofline.py
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mukesh b7c4c680aa analytical-viz: roofline tab — 'How hyperscalers pick GPU count' section
New section at the bottom of the Chip Roofline tab implementing the
three-axis GPU count decision:

  N_GPUs = max(capacity_floor, KV_headroom, throughput_SLO) × N_replicas

Interactive inputs: concurrent users, avg context/user, TPOT SLO.
Four KPI cards report each axis + the recommended total, with a
'binds:' delta chip showing which axis is the bottleneck.

  - Axis A (capacity):  PEs to hold weights alone
  - Axis B (KV):        PEs to hold weights + all KV of one replica's users
  - Axis C (throughput): replicas needed at B_at_SLO users each
  - Total: max(A,B) × N_replicas

Contextual caption explains what to do about the binding axis. If SLO
is infeasible (even B=1 exceeds SLO), an error block explains the
options (loosen SLO, shorten context, or scale up FLOPs/BW knobs).

Plus three collapsed expanders explaining the hybrid deployment
pattern hyperscalers use:
  - Layer 1: one elastic pool + PagedAttention + continuous batching
  - Layer 2: length-tier routing (standard vs long-context)
  - Layer 3: disaggregated prefill/decode (DistServe, Splitwise)

Pure additions in chip_roofline.py:
- max_batch_within_slo(machine, model, s_kv, slo_s) — analytical
  inverse of step_latency to find the largest per-replica B under SLO
- size_deployment(machine, model, n_users, avg_ctx, slo_s) — returns
  GpuSizingResult with all three axes + binding info

6 new tests cover: capacity scales with model size, KV grows with
users/context, binding axis flips with workload shape, tight SLO
shrinks max batch, weight-time-exceeds-SLO returns 0, total ==
per-replica × replicas.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-07-29 15:07:20 -07:00

520 lines
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"""Tests for chip_roofline: AI, B*, L*, per-token latency curves."""
from __future__ import annotations
import math
import pytest
from tests.analytical_visualization.chip_roofline import (
ai_sensitivity_curve,
arithmetic_intensity,
balance_context,
bound_regime,
critical_batch,
good_batch,
good_context,
knee_batch,
kv_bytes_per_token,
max_batch_within_slo,
memory_budget_curve_vs_batch,
memory_budget_curve_vs_skv,
per_token_latency_curve,
size_deployment,
step_latency_curve,
t_com,
t_mem_long,
t_mem_short,
total_active_params,
utilization_at,
)
from tests.analytical_visualization.model_config import (
FullConfig, MachineParams, ModelConfig, TopologyConfig,
)
from tests.analytical_visualization.model_presets import PRESETS
# ── Arithmetic intensity ────────────────────────────────────────────
def test_arithmetic_intensity_matches_ratio():
"""AI = peak_flops / bw_hbm — pure ratio, no util factor."""
m = MachineParams(peak_tflops_f16=8.0, bw_hbm_gbs=256.0)
assert arithmetic_intensity(m) == pytest.approx(8e12 / 256e9)
def test_ai_scales_with_flops_and_bandwidth():
m1 = MachineParams(peak_tflops_f16=8.0, bw_hbm_gbs=256.0)
m2 = MachineParams(peak_tflops_f16=16.0, bw_hbm_gbs=256.0)
m3 = MachineParams(peak_tflops_f16=8.0, bw_hbm_gbs=128.0)
assert arithmetic_intensity(m2) == pytest.approx(2 * arithmetic_intensity(m1))
assert arithmetic_intensity(m3) == pytest.approx(2 * arithmetic_intensity(m1))
# ── Critical batch B* ───────────────────────────────────────────────
def test_critical_batch_h100_reference():
"""H100-class: 989 TFLOPs BF16, 3.35 TB/s HBM3 → B* ≈ 295."""
m = MachineParams(peak_tflops_f16=989.0, bw_hbm_gbs=3350.0)
model = PRESETS["Llama 3 8B"].model # bf16 (b=2)
b_star = critical_batch(m, model)
assert b_star == pytest.approx(295, rel=0.05), b_star
def test_critical_batch_scales_with_sparsity():
"""MoE 8× sparsity gives 8× B*."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
b_dense = critical_batch(m, model, sparsity=1)
b_moe8 = critical_batch(m, model, sparsity=8)
assert b_moe8 == pytest.approx(8 * b_dense)
def test_critical_batch_bf16_formula():
"""For BF16 (b=2), B* = AI in flops-per-byte units → numerically."""
m = MachineParams(peak_tflops_f16=8.0, bw_hbm_gbs=256.0)
model = ModelConfig(bytes_per_elem=2)
ai = arithmetic_intensity(m)
assert critical_batch(m, model) == pytest.approx(ai), (
critical_batch(m, model), ai,
)
# ── Balance context L* ──────────────────────────────────────────────
def test_balance_context_positive_finite():
"""L* for a real model on real machine is a positive finite number."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
l_star = balance_context(m, model)
assert 0 < l_star < 1e9, l_star
def test_balance_context_scales_with_bandwidth():
"""L* = 2N*W/(C*kv_bpt): doubling HBM BW doubles L*.
Slower memory hits the KV wall at a shorter context. Machine-only
change so N_active and kv_bpt stay fixed."""
fast = MachineParams(bw_hbm_gbs=512.0)
slow = MachineParams(bw_hbm_gbs=256.0)
model = PRESETS["Llama 3 8B"].model
assert (balance_context(fast, model)
== pytest.approx(2 * balance_context(slow, model)))
# ── Knee ────────────────────────────────────────────────────────────
def test_knee_equals_b_star_at_short_context():
"""S_kv → 0: B_knee → B*."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
b_star = critical_batch(m, model)
assert knee_batch(m, model, s_kv=1) == pytest.approx(b_star, rel=1e-3)
def test_knee_diverges_at_balance_context():
"""S_kv = L*: knee is infinite; S_kv > L*: no knee (None)."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
l_star = balance_context(m, model)
assert knee_batch(m, model, s_kv=int(2 * l_star)) is None
# At 0.9 * L*, knee ~= 10 * B*; assert at least 5x to survive rounding.
below = knee_batch(m, model, s_kv=int(0.9 * l_star))
assert below is not None and below > 5 * critical_batch(m, model)
def test_knee_slides_right_with_context():
"""S_kv = L*/2 → B_knee = 2 * B*."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
b_star = critical_batch(m, model)
l_star = balance_context(m, model)
got = knee_batch(m, model, s_kv=int(l_star / 2))
assert got == pytest.approx(2 * b_star, rel=0.01), (got, 2 * b_star)
# ── Per-token latency curve ─────────────────────────────────────────
def test_latency_curve_monotonically_decreasing():
"""total_s must strictly decrease as batch increases (weight/B shrinks)."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
pts = per_token_latency_curve(m, model, [1, 2, 4, 8, 16, 32, 64],
s_kv=1024)
totals = [p.total_s for p in pts]
for a, b in zip(totals, totals[1:]):
assert b < a, (a, b)
def test_latency_curve_asymptotes_to_compute_plus_kv():
"""At very large B, total → compute + KV (weight/B → 0)."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
pts = per_token_latency_curve(m, model, [10_000_000], s_kv=1024)
p = pts[0]
assert p.total_s == pytest.approx(p.compute_s + p.kv_s, rel=1e-3)
def test_latency_at_b_star_is_roughly_2x_floor():
"""At B*, weight = compute (dense, S_kv small), so total ≈ 2 * compute."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
b_star = int(round(critical_batch(m, model)))
pts = per_token_latency_curve(m, model, [b_star], s_kv=1)
p = pts[0]
# weight_s ≈ compute_s at B*
assert p.weight_s == pytest.approx(p.compute_s, rel=0.05), (
p.weight_s, p.compute_s,
)
# ── Regime classification ───────────────────────────────────────────
def test_regime_memory_bound_at_b1():
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
assert bound_regime(m, model, batch=1, s_kv=1024) == "memory-bound"
def test_regime_kv_bound_past_balance_context():
"""S_kv > L* with reasonable batch → KV dominates."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
l_star = balance_context(m, model)
b_star = int(round(critical_batch(m, model)))
assert bound_regime(m, model, batch=b_star * 4,
s_kv=int(3 * l_star)) == "kv-bound"
# ── Component sanity ────────────────────────────────────────────────
def test_total_active_params_llama3_8b_ballpark():
"""Llama 3 8B — attn+FFN alone (no embeddings/LM head) is ~6.9B,
HF-reported total 8.03B. Guard the ballpark."""
n = total_active_params(PRESETS["Llama 3 8B"].model)
assert 6.5e9 < n < 8e9, n
def test_kv_bytes_per_token_llama3_8b():
"""Llama 3 8B: 2*8*128*2 bytes/layer/token × 32 layers = 131072 bytes."""
kv_bpt = kv_bytes_per_token(PRESETS["Llama 3 8B"].model)
assert kv_bpt == 2 * 8 * 128 * 2 * 32
# ── Regime terms + good-batch / good-context recommendations ──────
def test_t_mem_short_shrinks_with_batch():
"""t_mem_short = N·b/(W·B) — doubling B halves it."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
assert t_mem_short(m, model, 2) == pytest.approx(
t_mem_short(m, model, 1) / 2
)
def test_t_mem_long_equals_t_com_at_l_star():
"""L* is defined by t_mem_long(L*) == t_com. Cross-check."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
l_star = balance_context(m, model)
assert t_mem_long(m, model, int(round(l_star))) == pytest.approx(
t_com(m, model), rel=0.01,
)
def test_t_com_is_batch_independent():
"""t_com = 2·N/C. Constant — doesn't depend on B or S_kv."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
tc = t_com(m, model)
assert tc == pytest.approx(2 * total_active_params(model) / m.peak_flops)
def test_good_batch_is_two_b_star():
"""Recommendation is 2 × B* (Pope's rule)."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
rec = good_batch(m, model)
assert rec.effective == pytest.approx(2 * critical_batch(m, model))
assert rec.b_star == pytest.approx(critical_batch(m, model))
def test_good_batch_moe_scales_with_sparsity():
"""MoE sparsity=8 → recommended B is 8× dense recommendation."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
r_dense = good_batch(m, model, sparsity=1.0)
r_moe = good_batch(m, model, sparsity=8.0)
assert r_moe.effective == pytest.approx(8 * r_dense.effective)
def test_good_context_returns_l_star_as_ceiling():
"""Recommendation is L*; utilization drops past it."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
rec = good_context(m, model, s_kv=100)
assert rec.l_star == pytest.approx(balance_context(m, model))
assert rec.max_efficient == pytest.approx(rec.l_star)
def test_utilization_at_l_star_is_half():
"""At S_kv = L*, compute and KV read take equal time → 50% util."""
l_star = 3000.0
assert utilization_at(int(l_star), l_star) == pytest.approx(0.5)
def test_utilization_at_2_l_star_is_one_third():
"""At S_kv = 2·L*, util = 1/(1+2) = 33.3%."""
l_star = 3000.0
assert utilization_at(int(2 * l_star), l_star) == pytest.approx(1 / 3, rel=1e-3)
def test_utilization_at_zero_context_is_100_percent():
"""Zero context, no KV to read → all time is compute."""
assert utilization_at(0, 3000.0) == pytest.approx(1.0)
def test_utilization_drops_monotonically_with_context():
"""util(S_kv) is strictly decreasing."""
l_star = 3000.0
vals = [utilization_at(s, l_star) for s in [100, 1000, 3000, 6000, 30000]]
for a, b in zip(vals, vals[1:]):
assert b < a
# ── Step latency (undivided by B) ──────────────────────────────────
def test_step_weight_is_batch_invariant():
"""step_weight = N·b/W — same for every B (loaded once per step)."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
pts = step_latency_curve(m, model, [1, 8, 64, 512], s_kv=1024)
ws = [p.weight_s for p in pts]
assert all(w == pytest.approx(ws[0]) for w in ws), ws
def test_step_compute_linear_in_batch():
"""step_compute = 2·N·B/C — doubling B doubles compute."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
pts = step_latency_curve(m, model, [1, 2, 8], s_kv=1024)
assert pts[1].compute_s == pytest.approx(2 * pts[0].compute_s)
assert pts[2].compute_s == pytest.approx(8 * pts[0].compute_s)
def test_step_kv_linear_in_batch():
"""step_kv = B · S_kv · kv_bpt / W — linear in B."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
pts = step_latency_curve(m, model, [1, 4], s_kv=1024)
assert pts[1].kv_s == pytest.approx(4 * pts[0].kv_s)
def test_step_total_equals_per_token_times_batch():
"""The step and per-token views are just ÷ B / × B of each other."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
B_range = [1, 4, 16, 64]
s_kv = 1024
step_pts = step_latency_curve(m, model, B_range, s_kv=s_kv)
tok_pts = per_token_latency_curve(m, model, B_range, s_kv=s_kv)
for sp, tp in zip(step_pts, tok_pts):
assert sp.total_s == pytest.approx(tp.total_s * sp.batch)
def test_step_and_per_token_identical_at_b1():
"""At B=1, step latency == per-token cost (dividing by 1)."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
sp = step_latency_curve(m, model, [1], s_kv=1024)[0]
tp = per_token_latency_curve(m, model, [1], s_kv=1024)[0]
assert sp.total_s == pytest.approx(tp.total_s)
assert sp.weight_s == pytest.approx(tp.weight_s)
assert sp.compute_s == pytest.approx(tp.compute_s)
assert sp.kv_s == pytest.approx(tp.kv_s)
# ── PE memory budget sweeps ────────────────────────────────────────
def _budget_cfg():
"""Helper: real cfg with enough sharding to leave headroom."""
return FullConfig(
model=PRESETS["Llama 3 8B"].model,
topo=TopologyConfig(cp=2, tp=8, pp=1, b=1, s_kv=8192),
machine=MachineParams(),
)
def test_kv_grows_linear_with_skv():
cfg = _budget_cfg()
pts = memory_budget_curve_vs_skv(cfg, s_kv_range=[1024, 2048, 8192],
batch=1)
assert pts[1].kv_gb == pytest.approx(2 * pts[0].kv_gb, rel=1e-3)
assert pts[2].kv_gb == pytest.approx(8 * pts[0].kv_gb, rel=1e-3)
def test_kv_grows_linear_with_batch():
cfg = _budget_cfg()
pts = memory_budget_curve_vs_batch(cfg, b_range=[1, 2, 8],
s_kv=8192)
assert pts[1].kv_gb == pytest.approx(2 * pts[0].kv_gb, rel=1e-3)
assert pts[2].kv_gb == pytest.approx(8 * pts[0].kv_gb, rel=1e-3)
def test_weights_flat_across_skv_sweep():
"""Weight bytes are batch/S_kv-invariant — sharding fixed."""
cfg = _budget_cfg()
pts = memory_budget_curve_vs_skv(cfg, s_kv_range=[128, 8192, 1_000_000],
batch=1)
ws = [p.weights_gb for p in pts]
assert all(w == pytest.approx(ws[0]) for w in ws), ws
def test_over_budget_flag_trips_past_hbm():
"""Push S_kv until KV blows the HBM budget; over_budget must flip."""
cfg = _budget_cfg()
pts = memory_budget_curve_vs_skv(
cfg, s_kv_range=[1024, 10_000_000], batch=64,
)
# 10M tokens × B=64 KV should overflow the 6 GB budget.
assert not pts[0].over_budget, pts[0]
assert pts[-1].over_budget, pts[-1]
def test_free_gb_never_negative():
cfg = _budget_cfg()
pts = memory_budget_curve_vs_skv(
cfg, s_kv_range=[128, 10_000_000], batch=32,
)
for p in pts:
assert p.free_gb >= 0, p
# ── AI sensitivity to FLOPs / BW ──────────────────────────────────
def test_ai_scales_linearly_with_flops():
"""Doubling FLOPs doubles AI."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
pts = ai_sensitivity_curve(m, model, [1.0, 2.0, 4.0], axis="flops")
assert pts[1].ai == pytest.approx(2 * pts[0].ai)
assert pts[2].ai == pytest.approx(4 * pts[0].ai)
def test_ai_scales_inversely_with_bw():
"""Doubling BW halves AI."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
pts = ai_sensitivity_curve(m, model, [1.0, 2.0], axis="bw")
assert pts[1].ai == pytest.approx(pts[0].ai / 2)
def test_ai_sensitivity_b_star_tracks_ai_for_bf16():
"""For BF16, B* == AI. Curve should mirror."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model # BF16
pts = ai_sensitivity_curve(m, model, [0.5, 1.0, 4.0], axis="flops")
for p in pts:
assert p.b_star == pytest.approx(p.ai)
def test_ai_sensitivity_bad_axis_raises():
with pytest.raises(ValueError):
ai_sensitivity_curve(MachineParams(), PRESETS["Llama 3 8B"].model,
[1.0], axis="bogus")
# ── GPU sizing (three-axis) ────────────────────────────────────────
def test_capacity_floor_scales_with_model_size():
"""A model with 2× params needs ~2× PEs for weights alone (axis A)."""
m = MachineParams()
small = PRESETS["Llama 3 8B"].model
big = PRESETS["Llama 3 70B"].model
r_small = size_deployment(m, small, n_users=1, avg_ctx=1024,
tpot_slo_s=1.0)
r_big = size_deployment(m, big, n_users=1, avg_ctx=1024,
tpot_slo_s=1.0)
ratio = r_big.pes_axis_a_capacity / r_small.pes_axis_a_capacity
# 70B / 8B ≈ 8.75× params — allow generous tolerance
assert 5 < ratio < 12, (ratio, r_small, r_big)
def test_kv_headroom_scales_with_users_and_context():
"""Doubling n_users OR avg_ctx grows KV load roughly linearly."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
base = size_deployment(m, model, n_users=64, avg_ctx=4096,
tpot_slo_s=1.0)
twice_users = size_deployment(m, model, n_users=128, avg_ctx=4096,
tpot_slo_s=1.0)
twice_ctx = size_deployment(m, model, n_users=64, avg_ctx=8192,
tpot_slo_s=1.0)
# KV bytes doubled either way → axis-B PE count must strictly grow.
assert twice_users.pes_axis_b_kv > base.pes_axis_b_kv
assert twice_ctx.pes_axis_b_kv > base.pes_axis_b_kv
def test_binding_axis_flips_with_workload():
"""Huge N_users + short ctx → throughput binds.
Huge ctx + few users → kv (or capacity) binds."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
big_users = size_deployment(m, model, n_users=10_000, avg_ctx=1024,
tpot_slo_s=0.05)
long_ctx = size_deployment(m, model, n_users=1, avg_ctx=500_000,
tpot_slo_s=1.0)
assert big_users.binding_axis == "throughput", big_users
assert long_ctx.binding_axis in ("kv", "capacity"), long_ctx
def test_max_batch_shrinks_with_shorter_slo():
"""Tighter SLO → smaller B fits."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
loose = max_batch_within_slo(m, model, s_kv=1024, tpot_slo_s=1.0)
tight = max_batch_within_slo(m, model, s_kv=1024, tpot_slo_s=0.05)
assert tight < loose, (tight, loose)
def test_max_batch_returns_zero_when_weight_time_exceeds_slo():
"""If weight-fetch alone > SLO, no batch fits."""
m = MachineParams()
model = PRESETS["Llama 3 70B"].model
# 70B in BF16 = 140 GB. Reading at 256 GB/s takes ~547 ms.
# SLO of 100 ms cannot be met.
assert max_batch_within_slo(m, model, s_kv=100,
tpot_slo_s=0.1) == 0
def test_total_pes_equals_per_replica_times_replicas():
"""Sanity: total_pes = pes_per_replica × n_replicas."""
m = MachineParams()
model = PRESETS["Llama 3 8B"].model
r = size_deployment(m, model, n_users=500, avg_ctx=4096,
tpot_slo_s=0.1)
assert r.total_pes == r.pes_per_replica * r.n_replicas
# ── App wiring: tab exists on the Streamlit app ────────────────────
def test_roofline_tab_registered_in_app():
"""The new 'Chip roofline & B*' tab is listed in st.tabs and gets a
corresponding `with tab_roofline:` block."""
from pathlib import Path
src = (Path(__file__).parent / "app.py").resolve().read_text(
encoding="utf-8"
)
assert src.count('"Chip roofline & B*"') == 1
assert "with tab_roofline:" in src