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improve(llama): Faster apply_rotary_pos_emb #22785

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Apr 17, 2023
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improve(llama): Faster apply_rotary_pos_emb #22785

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9 changes: 5 additions & 4 deletions src/transformers/models/llama/modeling_llama.py
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Original file line number Diff line number Diff line change
Expand Up @@ -131,10 +131,11 @@ def rotate_half(x):


def apply_rotary_pos_emb(q, k, cos, sin, position_ids):
gather_indices = position_ids[:, None, :, None] # [bs, 1, seq_len, 1]
gather_indices = gather_indices.repeat(1, cos.shape[1], 1, cos.shape[3])
cos = torch.gather(cos.repeat(gather_indices.shape[0], 1, 1, 1), 2, gather_indices)
sin = torch.gather(sin.repeat(gather_indices.shape[0], 1, 1, 1), 2, gather_indices)
# The first two dimensions of cos and sin are always 1, so we can `squeeze` them.
cos = cos.squeeze((0, 1)) # [seq_len, dim]
sin = sin.squeeze((0, 1)) # [seq_len, dim]
cos = cos[position_ids].unsqueeze(1) # [bs, 1, seq_len, dim]
sin = sin[position_ids].unsqueeze(1) # [bs, 1, seq_len, dim]
q_embed = (q * cos) + (rotate_half(q) * sin)
k_embed = (k * cos) + (rotate_half(k) * sin)
return q_embed, k_embed
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