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fix(kernels): give the V tensor its own row pitch in the fp8 KV store #1

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Merged
ArqAlice merged 1 commit into from
Sep 4, 2026
Merged

fix(kernels): give the V tensor its own row pitch in the fp8 KV store #1

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11 changes: 7 additions & 4 deletions python/freetoken/kernel/triton/kv_quant.py
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Original file line number Diff line number Diff line change
Expand Up @@ -89,7 +89,9 @@ def _kv_quant_scatter_kernel(
k_scale,
v_scale,
idx_ptr,
stride_xs, # source row pitch, in elements (the qkv slice is wider than one row)
stride_xs, # K source row pitch, in elements (the qkv slice is wider than one row)
stride_vx, # V source row pitch. K and V need not share one: a .clamp() on one side
# leaves it densely packed, so reusing K's pitch reads V off its rows.
stride_kd, # K cache row pitch, in elements (== HEADS * D)
stride_vd,
stride_ks, # scale row pitch, in elements (== HEADS)
Expand All @@ -105,9 +107,9 @@ def _kv_quant_scatter_kernel(
d = tl.arange(0, BLOCK_D)
mask = d < D

src = t * stride_xs + h * D + d
xk = tl.load(k_src + src, mask=mask, other=0.0).to(tl.float32)
xv = tl.load(v_src + src, mask=mask, other=0.0).to(tl.float32)
off = h * D + d
xk = tl.load(k_src + t * stride_xs + off, mask=mask, other=0.0).to(tl.float32)
xv = tl.load(v_src + t * stride_vx + off, mask=mask, other=0.0).to(tl.float32)

# 448 == e4m3 finite max; 1e-10 is the amax floor of the activation quant in
# kernel/triton/fp8_block_linear.py (literals keep the kernel self-contained).
Expand Down Expand Up @@ -172,6 +174,7 @@ def quantize_kv_to_cache(
v_scale,
out_loc,
k.stride(0),
v.stride(0),
k_cache.stride(0),
v_cache.stride(0),
k_scale.stride(0),
Expand Down