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Add flash-attn op

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Woosuk Kwon 2024-04-17 18:02:28 +00:00
parent 25bbc21ef6
commit 5cb213c85e
1 changed files with 28 additions and 0 deletions
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vllm/model_executor/models/jax/ops/flash_attn.py Normal file
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import jax
from jax.experimental.pallas.ops.tpu.flash_attention import BlockSizes, flash_attention
_DEFAULT_BLOCK_SIZES = {
"block_q": 512,
"block_k_major": 512,
"block_k": 512,
"block_b": 2,
}
def flash_attn(
q: jax.Array, # [batch, seq_len, num_heads, head_size]
k: jax.Array, # [batch, seq_len, num_heads, head_size]
v: jax.Array, # [batch, seq_len, num_heads, head_size]
sm_scale: float,
) -> jax.Array: # [batch, seq_len, num_heads, head_size]
return flash_attention(
q.transpose(0, 2, 1, 3),
k.transpose(0, 2, 1, 3),
v.transpose(0, 2, 1, 3),
causal=True,
sm_scale=sm_scale,
block_sizes=BlockSizes(
min(_DEFAULT_BLOCK_SIZES["block_q"], q.shape[1]),
min(_DEFAULT_BLOCK_SIZES["block_k_major"], k.shape[1]),
min(_DEFAULT_BLOCK_SIZES["block_k"], k.shape[1]),
min(_DEFAULT_BLOCK_SIZES["block_b"], q.shape[0]))
).transpose(0, 2, 1, 3)