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optimize the performance of FlashBert Path for HPU #575

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Apr 16, 2025
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Original file line number Diff line number Diff line change
Expand Up @@ -323,19 +323,21 @@ def batch_type(self) -> Union[FlashBatch, PaddedBatch]:
def embed(self, batch: Union[FlashBatch, PaddedBatch]) -> List[Embedding]:
if isinstance(batch, PaddedBatch):
input_lens = batch.attention_mask.cumsum(-1)[:, -1].to(torch.int32)
max_input_lens = input_lens.max().item()
max_input_lens = 0 # This value will not be used
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Suggested change
max_input_lens = 0 # This value will not be used

NIT

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Hi, sorry , there may be misunderstanding. Here I commented "This value will not be used" means this variable can be any value, but we need to keep it here, as we need to pass it to L352

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@Narsil , can you help double check?

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I guess there are cases where the forward of the model does need a right value for this right? Otherwise why not removing it there?

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Well, this is a common file shared by CPU/XPU andd HPU devices. On CPU/XPU, we do need this variable with exact meaning, while on HPU, we do not have real varlen_attention API, so we pass attn_mask to replace its functionality. Here we just need to set a random value for max_input_lens. This line cannot be deleted, as we need to pass it to L352.

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Got it 👍

cu_seqlens = torch.cat(
(input_lens.new_tensor([0]), input_lens.cumsum(-1).int())
)
mask = batch.attention_mask.bool()
batch_size = input_lens.size(0)
bsz, tgt_len = mask.size()
min_val = torch.finfo(self.dtype).min
attn_mask = torch.full(
[batch_size, 1, 1, mask.shape[-1]],
fill_value=torch.finfo(self.dtype).min,
[bsz, 1, tgt_len, tgt_len],
fill_value=min_val,
device=self.device,
dtype=self.dtype,
)
attn_mask.masked_fill_(mask[:, None, None, :], 0)
expanded_mask = mask[:, None, None, :].expand(bsz, 1, tgt_len, tgt_len)
attn_mask = attn_mask.masked_fill(expanded_mask, 0.0)
elif isinstance(batch, FlashBatch):
cu_seqlens = batch.cu_seqlens
mask = None
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