add kv_cache to LLM (#244)

* init kv_cache pr

* pass past_key_values thru model fwd

* add qpadmask

* enable key_padding_mask for past_key_value

* use valid pos emb if using learned pos emb

* lint

* only compute past_position when needed

* nit

* Update examples/llm/src/models/layers/gpt_blocks.py

Co-authored-by: Daniel King <43149077+dakinggg@users.noreply.github.com>

* fix suggested edit

* dk pr cmt

---------

Co-authored-by: Daniel King <43149077+dakinggg@users.noreply.github.com>

examples/llm/src/models/layers/attention.py

@@ -23,12 +23,19 @@ def scaled_multihead_dot_product_attention(
     n_heads,
     softmax_scale=None,
     attn_bias=None,
+    query_padding_mask=None,
     key_padding_mask=None,
     is_causal=False,
     dropout_p=0.0,
     training=False,
     needs_weights=False,
 ):
+    if query_padding_mask is not None:
+        query = query.masked_fill(~query_padding_mask.unsqueeze(-1), 0)
+    if key_padding_mask is not None:
+        key = key.masked_fill(~key_padding_mask.unsqueeze(-1), 0)
+        value = value.masked_fill(~key_padding_mask.unsqueeze(-1), 0)
+
     q = rearrange(query, 'b s (h d) -> b h s d', h=n_heads)
     k = rearrange(key, 'b s (h d) -> b h d s', h=n_heads)  # includes key.t()
     v = rearrange(value, 'b s (h d) -> b h s d', h=n_heads)
@@ -50,6 +57,9 @@ def scaled_multihead_dot_product_attention(
             )
         attn_weight = attn_weight + attn_bias
 
+    if query_padding_mask is not None:
+        attn_weight = attn_weight.masked_fill(
+            ~query_padding_mask.view(b, 1, s_q, 1), -float('inf'))
     if key_padding_mask is not None:
         attn_weight = attn_weight.masked_fill(
             ~key_padding_mask.view((b, 1, 1, s_k)), -float('inf'))
@@ -65,14 +75,21 @@ def scaled_multihead_dot_product_attention(
 
     attn_weight = torch.softmax(attn_weight, dim=-1)
 
+    if query_padding_mask is not None:
+        attn_weight = attn_weight.masked_fill(
+            ~query_padding_mask.view(b, 1, s_q, 1), 0)
+    if key_padding_mask is not None:
+        attn_weight = attn_weight.masked_fill(
+            ~key_padding_mask.view(b, 1, 1, s_k), 0)
+
     if dropout_p:
         attn_weight = torch.nn.functional.dropout(attn_weight,
                                                   p=dropout_p,
                                                   training=training,
                                                   inplace=True)
 
     out = attn_weight.matmul(v)
-    out = rearrange(out, 'b h s d -> b s (h d)', h=n_heads)
+    out = rearrange(out, 'b h s d -> b s (h d)')
 
     if needs_weights:
         return out, attn_weight
@@ -94,6 +111,7 @@ def flash_attn_fn(
     n_heads,
     softmax_scale=None,
     attn_bias=None,
+    query_padding_mask=None,
     key_padding_mask=None,
     is_causal=False,
     dropout_p=0.0,
@@ -113,15 +131,13 @@ def flash_attn_fn(
 
     batch_size, seqlen = query.shape[:2]
 
+    if query_padding_mask is None:
+        query_padding_mask = torch.ones_like(query[:, :, 0], dtype=torch.bool)
     if key_padding_mask is None:
         key_padding_mask = torch.ones_like(key[:, :, 0], dtype=torch.bool)
 
-    if training:
-        pad_mask = key_padding_mask
-    else:
-        pad_mask = torch.ones_like(query[:, :, 0], dtype=torch.bool)
     query_unpad, indices_q, cu_seqlens_q, max_seqlen_q = bert_padding.unpad_input(
-        query, pad_mask)
+        query, query_padding_mask)
     query_unpad = rearrange(query_unpad, 'nnz (h d) -> nnz h d', h=n_heads)
 
     key_unpad, _, cu_seqlens_k, max_seqlen_k = bert_padding.unpad_input(
@@ -158,6 +174,7 @@ def triton_flash_attn_fn(
     n_heads,
     softmax_scale=None,
     attn_bias=None,
+    query_padding_mask=None,
     key_padding_mask=None,
     is_causal=False,
     dropout_p=0.0,
@@ -179,16 +196,31 @@ def triton_flash_attn_fn(
         raise NotImplementedError(
             f'attn_impl: triton cannot return attn weights.')
 
+    if query_padding_mask is not None:
+        query = query.masked_fill(~query_padding_mask.unsqueeze(-1), 0)
     if key_padding_mask is not None:
-        b_size, s_k = key_padding_mask.shape
+        key = key.masked_fill(~key_padding_mask.unsqueeze(-1), 0)
+        value = value.masked_fill(~key_padding_mask.unsqueeze(-1), 0)
+
+    if query_padding_mask is not None or key_padding_mask is not None:
+        b_size, s_q, s_k = query.size(0), 1, 1
+        if query_padding_mask is not None:
+            s_q = query_padding_mask.size(1)
+        if key_padding_mask is not None:
+            s_k = key_padding_mask.size(1)
 
         if attn_bias is not None:
             attn_bias = attn_bias.expand(b_size, -1, -1, -1)
         else:
-            attn_bias = query.new_zeros(b_size, 1, 1, s_k)
+            attn_bias = query.new_zeros(b_size, 1, s_q, s_k)
 
-        attn_bias = attn_bias.masked_fill(
-            ~key_padding_mask.view((b_size, 1, 1, s_k)), -float('inf'))
+        if query_padding_mask is not None:
+            attn_bias = attn_bias.masked_fill(
+                ~query_padding_mask.view((b_size, 1, s_q, 1)), -float('inf'))
+
+        if key_padding_mask is not None:
+            attn_bias = attn_bias.masked_fill(
+                ~key_padding_mask.view((b_size, 1, 1, s_k)), -float('inf'))
 
     query = rearrange(query, 'b s (h d) -> b s h d', h=n_heads)
     key = rearrange(key, 'b s (h d) -> b s h d', h=n_heads)
@@ -199,6 +231,9 @@ def triton_flash_attn_fn(
                                                     softmax_scale)
 
     output = attn_output.view(*attn_output.shape[:2], -1)
+    if query_padding_mask is not None:
+        output = output.masked_fill(~query_padding_mask.unsqueeze(-1), 0)
+
     return output, None
 
 
@@ -256,6 +291,7 @@ def __init__(self, cfg: DictConfig, device: Optional[str] = None):
 
     def forward(self,
                 x,
+                past_key_value=None,
                 attn_bias=None,
                 key_padding_mask=None,
                 is_causal=True,
@@ -266,12 +302,23 @@ def forward(self,
 
         query, key, value = qkv.chunk(3, dim=2)
 
+        query_padding_mask = None
+        if key_padding_mask is not None:
+            query_padding_mask = key_padding_mask[:, -query.size(1):]
+
         if self.attn_qk_ln:
             # Applying layernorm to qk
             dtype = query.dtype
             query = self.q_ln(query).to(dtype)
             key = self.k_ln(key).to(dtype)
 
+        if past_key_value is not None:
+            if len(past_key_value) == 0:
+                key = torch.cat([past_key_value[0], key], dim=1)
+                value = torch.cat([past_key_value[1], value], dim=1)
+
+            past_key_value = (key, value)
+
         if attn_bias is not None:
             attn_bias = attn_bias[:, :, -query.size(1):, -key.size(1):]
 
@@ -282,14 +329,15 @@ def forward(self,
             self.n_heads,
             softmax_scale=self.softmax_scale,
             attn_bias=attn_bias,
+            query_padding_mask=query_padding_mask,
             key_padding_mask=key_padding_mask,
             is_causal=is_causal,
             dropout_p=self.attn_dropout_p,
             training=self.training,
             needs_weights=needs_weights,
         )
 
-        return self.out_proj(context), attn_weights
+        return self.out_proj(context), attn_weights, past_key_value
 
 
 def attn_bias_shape(attn_impl, n_heads, seq_len, alibi, causal):

examples/llm/src/models/layers/gpt_blocks.py

@@ -3,7 +3,7 @@
 
 """GPT Blocks used for the GPT Model."""
 
-from typing import Optional
+from typing import Optional, Tuple
 
 import torch
 import torch.nn as nn
@@ -48,17 +48,19 @@ def __init__(self, cfg: DictConfig, device: Optional[str] = None):
     def forward(
         self,
         x: torch.Tensor,
+        past_key_value: Optional[Tuple[torch.Tensor]] = None,
         attn_bias: Optional[torch.Tensor] = None,
         key_padding_mask: Optional[torch.ByteTensor] = None,
         is_causal: bool = True,
-    ) -> torch.Tensor:
+    ) -> Tuple[torch.Tensor, Optional[Tuple[torch.Tensor]]]:
         a = self.ln_1(x)
-        b, _ = self.attn(a,
-                         attn_bias=attn_bias,
-                         key_padding_mask=key_padding_mask,
-                         is_causal=is_causal)
+        b, _, past_key_value = self.attn(a,
+                                         past_key_value=past_key_value,
+                                         attn_bias=attn_bias,
+                                         key_padding_mask=key_padding_mask,
+                                         is_causal=is_causal)
         x = x + self.resid_attn_dropout(b)
         m = self.ln_2(x)
         n = self.mlp(m)
         x = x + self.resid_mlp_dropout(n)
-        return x
+        return x, past_key_value

examples/llm/src/models/mosaic_gpt.py

@@ -8,7 +8,7 @@
 
 import math
 import warnings
-from typing import Optional
+from typing import List, Optional, Tuple
 
 import torch
 import torch.nn as nn
@@ -131,9 +131,11 @@ def _attn_bias(self, device, dtype):
 
         return self.attn_bias
 
-    def forward(self,
-                input_ids: torch.LongTensor,
-                key_padding_mask: Optional[torch.ByteTensor] = None):
+    def forward(
+            self,
+            input_ids: torch.LongTensor,
+            key_padding_mask: Optional[torch.ByteTensor] = None,
+            past_key_values: Optional[List[Tuple[torch.FloatTensor]]] = None):
         S = input_ids.size(1)
         assert (
             S <= self.cfg.max_seq_len
@@ -143,7 +145,25 @@ def forward(self,
         if self.alibi:
             x = tok_emb
         else:
-            pos = torch.arange(0, S, dtype=torch.long,
+            past_position = 0
+            if past_key_values is not None:
+                if len(past_key_values) != self.cfg.n_layers:
+                    raise ValueError(
+                        f'past_key_values must provide a past_key_value for each attention ' +\
+                        f'layer in the network ({len(past_key_values)=}; {self.cfg.n_layers=}).'
+                    )
+                # get the key tensor whose spec should be (batch, seq, dim), and
+                # collect the `seq`, so that the position embedding is shifted
+                past_position = past_key_values[0][0].size(1)
+
+            if S + past_position > self.cfg.max_seq_len:
+                raise ValueError(
+                    f'Cannot forward input with past sequence length {past_position} and current sequence length '
+                    f'{S + 1}, this model only supports total sequence length <= {self.cfg.max_seq_len}.'
+                )
+            pos = torch.arange(past_position,
+                               S + past_position,
+                               dtype=torch.long,
                                device=input_ids.device).unsqueeze(0)
             pos_emb = self.transformer.wpe(pos)  # type: ignore
             x = tok_emb + pos_emb
@@ -158,11 +178,18 @@ def forward(self,
             x = self.transformer.emb_drop(x_shrunk)
 
         attn_bias = self._attn_bias(device=x.device, dtype=x.dtype)
-        for block in self.transformer.blocks:  # type: ignore
-            x = block(x,
-                      attn_bias=attn_bias,
-                      key_padding_mask=key_padding_mask,
-                      is_causal=self.is_causal)
+
+        for b_idx, block in enumerate(self.transformer.blocks):  # type: ignore
+            past_key_value = past_key_values[
+                b_idx] if past_key_values is not None else None
+            x, past_key_value = block(x,
+                                      past_key_value=past_key_value,
+                                      attn_bias=attn_bias,
+                                      key_padding_mask=key_padding_mask,
+                                      is_causal=self.is_causal)
+            if past_key_values is not None:
+                past_key_values[b_idx] = past_key_value
+
         x = self.transformer.ln_f(x)  # type: ignore
         # output embedding weight tied to input embedding
         assert isinstance(self.transformer.wte, nn.Module)  # pyright

examples/llm/tests/test_flash_triton_torch.py

@@ -54,7 +54,7 @@ def test_attn_impl(attn_impl_0,
 
     key_padding_mask = torch.ones(n, s).to(device).bool()
 
-    def gen_bias(attn_impl, key_padding_mask):
+    def gen_bias(attn_impl):
         causal = True
         attn_bias = None
         bs = attention.attn_bias_shape(attn_impl,
@@ -72,24 +72,26 @@ def gen_bias(attn_impl, key_padding_mask):
                                 alibi=alibi,
                                 alibi_bias_max=8)
 
-        return attn_bias, key_padding_mask
+        return attn_bias
 
     x0 = torch.randn(n, s, f).to(device)
     x1 = x0.clone().detach()
     x0.requires_grad = True
     x1.requires_grad = True
 
     with torch.autocast(x0.device.type):
-        attn_bias, kpm = gen_bias(attn0.attn_impl, key_padding_mask)
-        y0, _ = attn0(x0,
-                      attn_bias=attn_bias,
-                      key_padding_mask=kpm,
-                      is_causal=True)
-        attn_bias, kpm = gen_bias(attn1.attn_impl, key_padding_mask)
-        y1, _ = attn1(x1,
-                      attn_bias=attn_bias,
-                      key_padding_mask=kpm,
-                      is_causal=True)
+        attn_bias = gen_bias(attn0.attn_impl)
+        y0, _, _ = attn0(x0,
+                         past_key_value=None,
+                         attn_bias=attn_bias,
+                         key_padding_mask=key_padding_mask,
+                         is_causal=True)
+        attn_bias = gen_bias(attn1.attn_impl)
+        y1, _, _ = attn1(x1,
+                         past_key_value=None,
+                         attn_bias=attn_bias,
+                         key_padding_mask=key_padding_mask,
+                         is_causal=True)
         y0 *= key_padding_mask.unsqueeze(-1)
         y1 *= key_padding_mask.unsqueeze(-1)
 
@@ -160,10 +162,11 @@ def gen_tca_mask():
     x1.requires_grad = True
 
     with torch.autocast(x0.device.type):
-        y0, _ = mmhsa(x0,
-                      attn_bias=None,
-                      key_padding_mask=key_padding_mask,
-                      is_causal=True)
+        y0, _, _ = mmhsa(x0,
+                         past_key_value=None,
+                         attn_bias=None,
+                         key_padding_mask=key_padding_mask,
+                         is_causal=True)
         y1, _ = tmhsa(x1,
                       x1,
                       x1,

examples/llm/tests/test_model.py

@@ -161,11 +161,12 @@ def test_attention_mechanism(batch_size=2):
 
     for block in model.model.transformer.blocks:
         a = block.ln_1(x)
-        b, attention_weights = block.attn(a,
-                                          attn_bias=attn_bias,
-                                          key_padding_mask=key_padding_mask,
-                                          is_causal=model.model.is_causal,
-                                          needs_weights=True)
+        b, attention_weights, _ = block.attn(a,
+                                             past_key_value=None,
+                                             attn_bias=attn_bias,
+                                             key_padding_mask=key_padding_mask,
+                                             is_causal=model.model.is_causal,
+                                             needs_weights=True)
 
         zerod_weights = (attention_weights == 0)
         assert torch.equal(expected_zerod_weights.expand(*zerod_weights.shape),