61 transformer blocks › 60 MoE blocks › Latent attention › Causal attention › Attention weights
Softmax
×no parametersnn.functional.softmax(attn_weights, dim=-1, dtype=torch.float32).to(query_states.dtype)
Normalize each query row over key positions.
- in
- [B batch, 64 heads, T queries, T keys]
- out
- [B batch, 64 heads, T queries, T keys]
In float32, then cast back to the query type (modeling_deepseek.py 834–836). The flash-attention path computes it inside flash_attn_func (1063, 1080).
Explanation
, , and index batch, head, query and key; runs over the keys.
Codemodeling_deepseek.py 799–840
cos, sin = self.rotary_emb(value_states, seq_len=kv_seq_len)
q_pe, k_pe = apply_rotary_pos_emb(q_pe, k_pe, cos, sin, position_ids)
query_states = k_pe.new_empty(bsz, self.num_heads, q_len, self.q_head_dim)
query_states[:, :, :, : self.qk_nope_head_dim] = q_nope
query_states[:, :, :, self.qk_nope_head_dim :] = q_pe
key_states = k_pe.new_empty(bsz, self.num_heads, q_len, self.q_head_dim)
key_states[:, :, :, : self.qk_nope_head_dim] = k_nope
key_states[:, :, :, self.qk_nope_head_dim :] = k_pe
if past_key_value is not None:
cache_kwargs = {"sin": sin, "cos": cos} # Specific to RoPE models
key_states, value_states = past_key_value.update(
key_states, value_states, self.layer_idx, cache_kwargs
)
attn_weights = (
torch.matmul(query_states, key_states.transpose(2, 3)) * self.softmax_scale
)
if attn_weights.size() != (bsz, self.num_heads, q_len, kv_seq_len):
raise ValueError(
f"Attention weights should be of size {(bsz, self.num_heads, q_len, kv_seq_len)}, but is"
f" {attn_weights.size()}"
)
assert attention_mask is not None
if attention_mask is not None:
if attention_mask.size() != (bsz, 1, q_len, kv_seq_len):
raise ValueError(
f"Attention mask should be of size {(bsz, 1, q_len, kv_seq_len)}, but is {attention_mask.size()}"
)
attn_weights = attn_weights + attention_mask
# upcast attention to fp32
attn_weights = nn.functional.softmax(
attn_weights, dim=-1, dtype=torch.float32
).to(query_states.dtype)
attn_weights = nn.functional.dropout(
attn_weights, p=self.attention_dropout, training=self.training
)
attn_output = torch.matmul(attn_weights, value_states)Sources1
Direct evidence
The rotary parts are rotated; each head’s query and key join their non-rotated and rotated parts, the key’s rotated part being the shared rotary key; scores are scaled, masked by the causal mask, normalized and used to mix values.
mla-prefill · moonshotai/Kimi-K2-Instruct / modeling_deepseek.py
Pinned revision fd1984e2b7a3 ↗ · lines 799–840
Read code excerpt
cos, sin = self.rotary_emb(value_states, seq_len=kv_seq_len)
q_pe, k_pe = apply_rotary_pos_emb(q_pe, k_pe, cos, sin, position_ids)
query_states = k_pe.new_empty(bsz, self.num_heads, q_len, self.q_head_dim)
query_states[:, :, :, : self.qk_nope_head_dim] = q_nope
query_states[:, :, :, self.qk_nope_head_dim :] = q_pe
key_states = k_pe.new_empty(bsz, self.num_heads, q_len, self.q_head_dim)
key_states[:, :, :, : self.qk_nope_head_dim] = k_nope
key_states[:, :, :, self.qk_nope_head_dim :] = k_pe
if past_key_value is not None:
cache_kwargs = {"sin": sin, "cos": cos} # Specific to RoPE models
key_states, value_states = past_key_value.update(
key_states, value_states, self.layer_idx, cache_kwargs
)
attn_weights = (
torch.matmul(query_states, key_states.transpose(2, 3)) * self.softmax_scale
)
if attn_weights.size() != (bsz, self.num_heads, q_len, kv_seq_len):
raise ValueError(
f"Attention weights should be of size {(bsz, self.num_heads, q_len, kv_seq_len)}, but is"
f" {attn_weights.size()}"
)
assert attention_mask is not None
if attention_mask is not None:
if attention_mask.size() != (bsz, 1, q_len, kv_seq_len):
raise ValueError(
f"Attention mask should be of size {(bsz, 1, q_len, kv_seq_len)}, but is {attention_mask.size()}"
)
attn_weights = attn_weights + attention_mask
# upcast attention to fp32
attn_weights = nn.functional.softmax(
attn_weights, dim=-1, dtype=torch.float32
).to(query_states.dtype)
attn_weights = nn.functional.dropout(
attn_weights, p=self.attention_dropout, training=self.training
)
attn_output = torch.matmul(attn_weights, value_states)