diff --git a/STAGE_D.md b/STAGE_D.md index 795be9cb..bb41f165 100644 --- a/STAGE_D.md +++ b/STAGE_D.md @@ -748,30 +748,45 @@ The following are real potential wins but go beyond what the V4 paper explicitly --- -## ⚡ CURRENT ACTION (2026-05-23 19:20 UTC) +## ⚡ CURRENT ACTION (2026-05-23 19:25 UTC) -**D1.3 SMEM-P Rank Mismatch Issue — DEBUGGING IN PROGRESS:** +**D1.3 SMEM-P — MANUAL COPY ATTEMPT FAILED:** -**Problem:** SMEM-P copy fails with rank mismatch: source rank 4, destination rank 5. -- Source `tSMEM_CPYrP_qk`: `((64, 8), 128, 1, 1)` rank 4 -- Destination `tSMEM_CPYsP`: `(((128, 16), 8), 16, 1, (4, 2), 1)` rank 5 -- Error: "Expected source and destination tensors to have the same rank" +**Problem:** `make_tiled_copy_C` creates incompatible partitions: +- Source partition `tSMEM_CPYrP_qk`: size=65536 elements (rank 4) +- Destination partition `tSMEM_CPYsP`: size=2097152 elements (rank 5) — 32× larger! +- Manual copy attempted but size mismatch prevents element-wise mapping. **Debug Findings:** -1. `sP` shape: `((128, 16), 1, (4, 2), 1)` (4 modes) — PV A-operand SMEM layout -2. `rP_bf16_qk` shape: `((128, 128), 1, 1)` (3 modes) — QK C-fragment layout -3. Using `make_tiled_copy_C(smem_copy_atom, qk_mma)` with `tcgen05.copy.St32x32bOp` BF16 atom -4. `partition_S` produces rank 4 from rank 3 input (adds a mode) -5. `partition_D` produces rank 5 from rank 4 input (adds a mode) +1. `make_tiled_copy_C(smem_copy_atom, qk_mma)` partitions threads by QK C-fragment layout +2. But `sP` has PV A-operand SMEM layout — incompatible tiling structure +3. `partition_S` and `partition_D` produce tensors with different element counts (65536 vs 2M) +4. This confirms "helpers are a trap" — they assume compatible layouts -**Root Cause Hypothesis:** -The tiled copy created by `make_tiled_copy_C` with `qk_mma` expects source/destination tensors with specific tiling structure. `sP` (PV A-operand layout) doesn't match that structure. +**Root Cause:** QK C-fragment tiling and PV A-operand tiling are fundamentally different. A tiled copy operation expects source and destination to have same tiling pattern. -**Possible Solutions (from STAGE_D.md):** -1. Try different `group_modes` combinations -2. Implement manual SMEM copy without helpers (bypass `make_tiled_copy_C`) -3. Compute SMEM addresses manually from QK partition → PV A-operand mapping +**Realization:** We need SMEM as rendezvous point with manual addressing, not automatic tiled copy. -**Blocked:** Need to understand correct approach for SMEM-P copy given "helpers are a trap" warning. +**Possible Paths Forward:** +1. **Manual SMEM addressing:** Compute SMEM addresses directly from QK C-fragment coordinates +2. **Change sP layout:** Make `sP` have QK C-fragment layout (not PV A-operand) +3. **Abandon helpers entirely:** Implement complete manual copy without `make_tiled_copy_C` -**Next:** Investigate manual copy approach or try `group_modes(sP, 0, 4)` to flatten all modes. \ No newline at end of file +**Blocked:** Need to decide on correct approach. Manual addressing seems most aligned with "helpers are a trap" warning. + +**Mike says:** "Youre gonna need to do manual SMEM addressing. It may take you a few hours, but I trust you can do it." + +**Decision:** Manual SMEM addressing it is. Abandon `make_tiled_copy_C` entirely. + +**Approach:** +1. Get thread's position in QK C-fragment partition +2. Compute which P values this thread owns (range in QK C-fragment space) +3. For each P value, compute destination SMEM address in PV A-operand layout +4. Write P values to computed SMEM addresses + +**Implementation Plan:** +- Use `cute.coord` to get thread's logical coordinates in QK C-fragment partition +- Compute mapping: (thread_coord, element_idx) → SMEM_offset +- Write via `sP[smem_offset] = p_value` + +**Expected Complexity:** Few hours. Need to understand QK C-fragment layout and PV A-operand SMEM layout coordinate systems. \ No newline at end of file