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Remove a branch with pl.when in fetching bkv #1239

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8fe971f
Remove a branch with pl.when in fetching bkv
rupengliu-meta Dec 4, 2025
b85eb24
Merge branch 'main' into rupliu/k3
rupengliu-meta Dec 4, 2025
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23 changes: 10 additions & 13 deletions tpu_inference/kernels/ragged_paged_attention/v3/kernel.py
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Original file line number Diff line number Diff line change
Expand Up @@ -463,19 +463,16 @@ def loop_body(i, offset):
unroll=False,
)

# Fetch kv directly from new kv.
@pl.when(bkv_sz_frm_new > 0)
def _fetch_bkv_from_new_kv():
new_kv_len_start = q_end - kv_left_frm_new
debug_print("[RPA debug] new_kv_len_start={}",
new_kv_len_start)
debug_print("[RPA debug] offset_in_bkv={}", offset)
_async_copy(
kv_hbm_ref.at[pl.ds(new_kv_len_start, bkv_sz_frm_new)],
vmem_ref.at[pl.ds(offset, bkv_sz_frm_new)],
sem,
wait,
)
size = lax.select(bkv_sz_frm_new > 0, bkv_sz_frm_new, 0)
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@vanbasten23 vanbasten23 Dec 4, 2025

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so if size==0, then the dma will be a no-op?

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@rupengliu-meta rupengliu-meta Dec 4, 2025

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yes, exactly

new_kv_len_start = q_end - kv_left_frm_new
debug_print("[RPA debug] new_kv_len_start={}", new_kv_len_start)
debug_print("[RPA debug] offset_in_bkv={}", offset)
_async_copy(
kv_hbm_ref.at[pl.ds(new_kv_len_start, size)],
vmem_ref.at[pl.ds(offset, size)],
sem,
wait,
)

return kv_len_start + offset, bkv_sz_frm_new
else:
Expand Down
23 changes: 10 additions & 13 deletions tpu_inference/kernels/ragged_paged_attention/v3/kernel_hd64.py
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Original file line number Diff line number Diff line change
Expand Up @@ -520,19 +520,16 @@ def loop_body(i, offset):
unroll=False,
)

# Fetch kv directly from new kv.
@pl.when(bkv_sz_frm_new > 0)
def _fetch_bkv_from_new_kv():
new_kv_len_start = q_end - kv_left_frm_new
debug_print("[RPA debug] new_kv_len_start={}",
new_kv_len_start)
debug_print("[RPA debug] offset_in_bkv={}", offset)
_async_copy(
kv_hbm_ref.at[pl.ds(new_kv_len_start, bkv_sz_frm_new)],
vmem_ref.at[pl.ds(offset, bkv_sz_frm_new)],
sem,
wait,
)
size = lax.select(bkv_sz_frm_new > 0, bkv_sz_frm_new, 0)
new_kv_len_start = q_end - kv_left_frm_new
debug_print("[RPA debug] new_kv_len_start={}", new_kv_len_start)
debug_print("[RPA debug] offset_in_bkv={}", offset)
_async_copy(
kv_hbm_ref.at[pl.ds(new_kv_len_start, size)],
vmem_ref.at[pl.ds(offset, size)],
sem,
wait,
)

return kv_len_start + offset, bkv_sz_frm_new
else:
Expand Down