Replace each kernel's local one-shot partial with a Tile-0 bootstrap + a
``scratch_scope``-wrapped merge loop. Per-rank scratch is now bounded by
``TILE_S_KV = 1024`` regardless of ``S_local``, lifting the long-context S
ceiling. Backward compatible at ``S_local <= TILE_S_KV`` (loop body is
empty; op_log structurally identical to today).
Framework: extend ``memory_store.read`` to support partial reads at
offsets within a stored region. Models real Triton ``tl.load(ptr+offset,
shape=...)`` — needed because each tile loads ``k_ptr + tile_start*row_bytes``
for its sub-slice of the per-rank KV region.
prefill_long is intentionally left untiled. Its ring loop carries
full-slice ``Kc``/``Vc`` for ``tl.send`` between CUBEs, so tile-sweeping
step 0 wouldn't shrink the kernel's actual scratch footprint. Lifting
prefill_long's ceiling requires a tile-granular ring rewrite — separate
phase. Docstring + inline comments cleaned to reflect the current shape.
Docstrings across all 4 GQA kernels: drop P1a/P2a/P2b/P6a/P6b lineage
paragraphs and historical deviation lists; describe each kernel by what
it does, not how it got here. Add explicit ``# Local attention`` /
``# Communication`` section headers.
Tests: new ``tests/attention/test_gqa_tile_sweep.py`` with 5 tests
covering single-tile op_log stability, multi-tile ``copy_to`` emission
across all 3 refactored kernels, and the headline ceiling-lift
(decode_long at S_kv=256K). Full focused regression green: 85/85 across
``tests/attention/`` + Phase E + TL discipline tests.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
mukesh
91cdfebb67