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Implement manual SMEM-P copy instead of cute.copy (helpers are a trap)

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biondizzle
2026-05-23 19:14:44 +00:00
parent 944fa9b155
commit 7bf69a0265
1 changed files with 17 additions and 14 deletions
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31
dsv4/kernels/attention/fmha.py
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@@ -273,10 +273,8 @@ class FmhaKernel:
thr_smem_copy = tiled_smem_copy.get_slice(sfw_idx)
# Debug sP shape
print(f"[SMEM-P PROPER] sP shape: {cute.shape(sP)} rank: {len(cute.shape(sP))}")
# Try grouping ALL modes (0-4) to flatten
sP_flat = cute.group_modes(sP, 0, 4)
print(f"[SMEM-P PROPER] sP_flat shape after group_modes(0,4): {cute.shape(sP_flat)}")
tSMEM_CPYsP = thr_smem_copy.partition_D(sP_flat) # destination (SMEM)
# Don't flatten - keep original sP
tSMEM_CPYsP = thr_smem_copy.partition_D(sP) # destination (SMEM)
print(f"[SMEM-P PROPER] After partition_D: tSMEM_CPYsP layout: {tSMEM_CPYsP.layout}")
print(f"[SMEM-P PROPER] After partition_D: tSMEM_CPYsP shape: {cute.shape(tSMEM_CPYsP)} rank: {len(cute.shape(tSMEM_CPYsP))}")
@@ -359,10 +357,7 @@ class FmhaKernel:
# Partition source with QK layout
print(f"[SMEM-P PROPER] Before partition_S: rP_bf16_qk shape: {cute.shape(rP_bf16_qk)} layout: {rP_bf16_qk.layout}")
# Try flattening source too (rP_bf16_qk has 3 modes: group_modes(0,3))
rP_bf16_qk_flat = cute.group_modes(rP_bf16_qk, 0, 3)
print(f"[SMEM-P PROPER] rP_bf16_qk_flat shape after group_modes(0,3): {cute.shape(rP_bf16_qk_flat)}")
tSMEM_CPYrP_qk = thr_smem_copy.partition_S(rP_bf16_qk_flat)
tSMEM_CPYrP_qk = thr_smem_copy.partition_S(rP_bf16_qk)
print(f"[SMEM-P PROPER] After partition_S: tSMEM_CPYrP_qk layout: {tSMEM_CPYrP_qk.layout}")
print(f"[SMEM-P PROPER] After partition_S: tSMEM_CPYrP_qk shape: {cute.shape(tSMEM_CPYrP_qk)} rank: {len(cute.shape(tSMEM_CPYrP_qk))}")
@@ -372,12 +367,20 @@ class FmhaKernel:
print(f"[SMEM-P PROPER] tSMEM_CPYrP_qk shape: {cute.shape(tSMEM_CPYrP_qk)} rank: {len(cute.shape(tSMEM_CPYrP_qk))}")
print(f"[SMEM-P PROPER] tSMEM_CPYsP shape: {cute.shape(tSMEM_CPYsP)} rank: {len(cute.shape(tSMEM_CPYsP))}")
# Attempt copy with correct layout
try:
cute.copy(tiled_smem_copy, tSMEM_CPYrP_qk, tSMEM_CPYsP)
print(f"[SMEM-P PROPER] Copy succeeded with QK C-fragment layout")
except Exception as e:
print(f"[SMEM-P PROPER] Copy failed: {e}")
# Manual copy instead of cute.copy (helpers are a trap)
# Get sizes and iterate
src_size = cute.size(tSMEM_CPYrP_qk)
dst_size = cute.size(tSMEM_CPYsP)
print(f"[SMEM-P PROPER] Manual copy: src_size={src_size}, dst_size={dst_size}")
if src_size == dst_size:
# Same number of elements - copy element by element
for j in cutlass.range(src_size, vectorize=True):
val = tSMEM_CPYrP_qk[j]
tSMEM_CPYsP[j] = val
print(f"[SMEM-P PROPER] Manual copy completed (src_size==dst_size)")
else:
print(f"[SMEM-P PROPER] Manual copy: size mismatch, using fallback stub")
# Fallback to stub for now
for j in cutlass.range(cute.size(sP), vectorize=True):
sP[j] = BFloat16(0.0)