Second case in the GQA decode 4-cases comparative study per
GQA_full_deck.pptx slide 11. Case 2 replicates K, V across all 8
cubes × 8 PEs (the slide-11 8 KB/tok/PE memory waste) and has zero
inter-rank comm. For B=1 (single-user decode default), only PE 0
of CUBE 0 has work — the inherent PE-TP waste slide 11 calls out.
Changes:
- New kernel: src/kernbench/benches/_gqa_attention_decode_cube_repl_pe_tp.py
Simplest of the 4 cases. Active rank loads full Q/K/V from HBM,
computes attention via S_kv tile sweep with online-softmax merge,
writes O. All non-(0,0) ranks early-return. No tl.send/recv.
- src/kernbench/benches/milestone_gqa_decode_4cases.py:
- Add panel single_kv_group_decode_gqa_cube_repl_pe_tp (Case 2)
to _PANELS and _PANEL_DISPATCH.
- Add _run_decode_panel_cube_repl_pe_tp helper: DPPolicy K/V/Q/O
= cube=replicate, pe=replicate (models 8× memory waste).
- Extend _make_bench_fn to dispatch kind="decode_cube_repl_pe_tp"
to the new runner.
- tests/attention/test_milestone_gqa_decode_4cases.py:
4 new tests assert Case 2 contract: panel registered, smoke
completion, zero ipcq_copy (no comm), single dma_write from cube 0.
Verification: 8/8 tests pass (4 Case 4 anchor + 4 new Case 2).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
mukesh
5672c8f3ef