First milestone of the decode 4-cases comparative study per
GQA_full_deck.pptx slides 11-17. Case 4 (Cube-SP × PE-SP, the optimal
case per slide 11) is structurally the existing _gqa_attention_decode_long
at sub_w=4 (Increment 2's lrab-adapted center-root reduce). This commit
wires it into a dedicated bench so the remaining cases land alongside.
Changes:
- New bench: src/kernbench/benches/milestone_gqa_decode_4cases.py
Houses the 4 case panels under one milestone-gqa-decode-4cases entry
(gated by GQA_DECODE_4CASES_RUN=1; output to
1H_milestone_output/gqa_decode_4cases/sweep.json). Cases 1-3 are
TBD in subsequent sub-increments (5C.A/B/C).
- New panel: single_kv_group_decode_gqa_cube_sp_pe_sp
C=8, P=8, sub_w=4, T_q=1, S_kv=131_072, d_head=128, h_q=8, h_kv=1.
- src/kernbench/benches/milestone_gqa_headline.py: _run_decode_panel
extended with keyword-only sub_w/T_q/d_head/h_q/h_kv overrides
(defaults preserve existing-panel behaviour).
- tests/attention/test_milestone_gqa_decode_4cases.py: 4 new tests
asserting registration, smoke completion, reduce-to-root at the lrab
center cube (cube 6), and the predicted 189-ipcq Case-4 traffic
pattern (168 intra-CUBE + 21 inter-CUBE lrab Phase 1+2).
- tests/attention/test_milestone_gqa_headline.py: rename
test_sweep_json_has_four_panels -> test_sweep_json_has_expected_panels
and switch hardcoded 4 to len(PANELS) (the panel set grew to 5
with Increment 5's single_kv_group_prefill_gqa_c8_p8).
Deviation noted: slide 13 prescribes AllReduce on (m,ℓ,O); our kernel
does reduce-to-root (only the lrab center cube has the answer) per
ADR-0060 §4. Treated as the kernbench Case-4 baseline.
Verification: all 4 new tests pass; 90 regression tests pass; the
previously-failing test_sweep_json_has_four_panels now passes under
its renamed form.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
