feat(server): add support for llamav2 (#633)

Author: Narsil

server/text_generation_server/models/custom_modeling/flash_llama_modeling.py

@@ -39,6 +39,7 @@
     TensorParallelEmbedding,
     PositionRotaryEmbedding,
     TensorParallelHead,
+    get_linear,
 )
 
 
@@ -59,7 +60,8 @@ def forward(self, hidden_states, residual=None):
                 hidden_states += residual
             residual = hidden_states
 
-            variance = hidden_states.to(torch.float32).pow(2).mean(-1, keepdim=True)
+            hidden_states = hidden_states.to(torch.float32)
+            variance = hidden_states.pow(2).mean(-1, keepdim=True)
             hidden_states = hidden_states * torch.rsqrt(
                 variance + self.variance_epsilon
             )
@@ -94,6 +96,27 @@ def forward(self, hidden_states, residual=None):
             return normed_hidden_states, res
 
 
+def _load_gqa(config, prefix: str, weights):
+    w = [
+        weights.get_sharded(f"{prefix}.q_proj.weight", dim=0),
+        weights.get_sharded(f"{prefix}.k_proj.weight", dim=0),
+        weights.get_sharded(f"{prefix}.v_proj.weight", dim=0),
+    ]
+    weight = torch.cat(w, dim=0)
+    weight = weight.to(dtype=weights.dtype).to(device=weights.device)
+    bias = None
+    assert config.hidden_size % config.num_attention_heads == 0
+    head_size = config.hidden_size // config.num_attention_heads
+    assert config.num_attention_heads % weights.process_group.size() == 0
+    num_heads = config.num_attention_heads // weights.process_group.size()
+    num_key_value_heads = config.num_key_value_heads // weights.process_group.size()
+    assert list(weight.shape) == [
+        (num_heads + 2 * num_key_value_heads) * head_size,
+        config.hidden_size,
+    ], f"{list(weight.shape)} != {[(num_heads + 2 * config.num_key_value_heads) * head_size, config.hidden_size]}"
+    return TensorParallelColumnLinear(get_linear(weight, bias, config.quantize))
+
+
 class FlashLlamaAttention(torch.nn.Module):
     def __init__(
         self,
@@ -118,22 +141,29 @@ def __init__(
                 f"and `num_shards`: {weights.process_group.size()}"
             )
         self.num_heads = self.num_heads // weights.process_group.size()
-        self.query_key_value = TensorParallelColumnLinear.load_multi(
-            config,
-            prefixes=[f"{prefix}.q_proj", f"{prefix}.k_proj", f"{prefix}.v_proj"],
-            dim=0,
-            weights=weights,
-            bias=False,
+        self.num_key_value_heads = (
+            config.num_key_value_heads // weights.process_group.size()
         )
+        if config.num_attention_heads != config.num_key_value_heads:
+            self.query_key_value = _load_gqa(config, prefix, weights)
+        else:
+            self.query_key_value = TensorParallelColumnLinear.load_multi(
+                config,
+                prefixes=[f"{prefix}.q_proj", f"{prefix}.k_proj", f"{prefix}.v_proj"],
+                dim=0,
+                weights=weights,
+                bias=False,
+            )
         self.o_proj = TensorParallelRowLinear.load(
             config,
             prefix=f"{prefix}.o_proj",
             weights=weights,
             bias=False,
         )
+        self.num_groups = self.num_heads // self.num_key_value_heads
         self.kv_head_mapping = torch.arange(
-            0, self.num_heads, dtype=torch.int32, device=weights.device
-        )
+            0, self.num_key_value_heads, dtype=torch.int32, device=weights.device
+        ).repeat_interleave(self.num_groups)
 
     def forward(
         self,
@@ -148,26 +178,33 @@ def forward(
         max_s,
     ):
         qkv = self.query_key_value(hidden_states)
-        qkv = qkv.view(-1, 3, self.num_heads, self.head_size)
+        query, kv = qkv.split(
+            [
+                self.head_size * self.num_heads,
+                2 * self.head_size * self.num_key_value_heads,
+            ],
+            dim=1,
+        )
+        query = query.view(-1, self.num_heads, self.head_size)
+        kv = kv.view(-1, 2, self.num_key_value_heads, self.head_size)
 
-        # Inplace rotary
-        self.rotary_emb(qkv[:, 0], cos, sin)
-        self.rotary_emb(qkv[:, 1], cos, sin)
+        self.rotary_emb(query, cos, sin)
+        self.rotary_emb(torch.select(kv, dim=1, index=0), cos, sin)
 
         vllm_cache_ops.reshape_and_cache(
-            qkv[:, 1], qkv[:, 2], kv_cache[0], kv_cache[1], slots
+            kv[:, 0], kv[:, 1], kv_cache[0], kv_cache[1], slots
         )
 
         # output tensor
-        attn_output = torch.empty_like(qkv[:, 0])
+        attn_output = torch.empty_like(query)
 
         # Prefill
         if cu_seqlen_prefill is not None:
             # flash attention
             attention(
-                qkv[:, 0],
-                qkv[:, 1],
-                qkv[:, 2],
+                query,
+                torch.select(kv, dim=1, index=0),
+                torch.select(kv, dim=1, index=1),
                 attn_output,
                 cu_seqlen_prefill,
                 max_s,
@@ -179,7 +216,7 @@ def forward(
             block_size = kv_cache[1].shape[3]
             vllm_attention_ops.single_query_cached_kv_attention(
                 attn_output,
-                qkv[:, 0],
+                query,
                 kv_cache[0],
                 kv_cache[1],
                 self.kv_head_mapping,
@@ -316,6 +353,7 @@ def __init__(self, config, weights):
 
         self.head_size = self.layers[0].self_attn.head_size
         self.num_heads = self.layers[0].self_attn.num_heads
+        self.num_key_value_heads = self.layers[0].self_attn.num_key_value_heads
 
     def forward(
         self,

server/text_generation_server/models/flash_llama.py

@@ -69,7 +69,7 @@ def __init__(
             model=model,
             tokenizer=tokenizer,
             num_layers=len(model.model.layers),
-            num_kv_heads=model.model.num_heads,
+            num_kv_heads=model.model.num_key_value_heads,
             head_size=model.model.head_size,
             dtype=dtype,
             device=device,