Gemma2 reward model support (#1954)

docs/references/supported_models.md

@@ -40,7 +40,8 @@
 
 - LlamaForSequenceClassification
   - `python -m sglang.launch_server --model-path Skywork/Skywork-Reward-Llama-3.1-8B-v0.2 --is-embedding`
-
+- Gemma2ForSequenceClassification
+  - `python -m sglang.launch_server --model-path Skywork/Skywork-Reward-Gemma-2-27B-v0.2 --is-embedding`
 
 ## How to Support a New Model
 

python/sglang/srt/models/gemma2_reward.py

+"""
+Copyright 2023-2024 SGLang Team
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+from typing import Iterable, Optional, Tuple
+
+import torch
+from torch import nn
+from transformers import Gemma2Config
+from vllm.model_executor.model_loader.weight_utils import default_weight_loader
+
+from sglang.srt.layers.pooler import EmbeddingPoolerOutput, Pooler, PoolingType
+from sglang.srt.layers.quantization.base_config import QuantizationConfig
+from sglang.srt.model_executor.forward_batch_info import ForwardBatch
+from sglang.srt.models.gemma2 import Gemma2ForCausalLM, Gemma2Model
+
+
+class Gemma2ForSequenceClassification(nn.Module):
+    def __init__(
+        self,
+        config: Gemma2Config,
+        quant_config: Optional[QuantizationConfig] = None,
+        cache_config=None,
+    ) -> None:
+        super().__init__()
+        self.config = config
+        self.torchao_config = None
+        self.quant_config = quant_config
+        self.num_labels = config.num_labels
+        self.model = Gemma2Model(config, quant_config=quant_config)
+        self.score = nn.Linear(config.hidden_size, self.num_labels, bias=False)
+        self.pooler = Pooler(pooling_type=PoolingType.LAST, normalize=False)
+
+        self.eos_token_id = config.eos_token_id
+
+    @torch.no_grad()
+    def forward(
+        self,
+        input_ids: torch.Tensor,
+        positions: torch.Tensor,
+        forward_batch: ForwardBatch,
+        input_embeds: torch.Tensor = None,
+        get_embedding: bool = True,
+    ) -> EmbeddingPoolerOutput:
+        assert (
+            get_embedding
+        ), "Gemma2ForSequenceClassification is only used for embedding"
+
+        hidden_states = self.model(input_ids, positions, forward_batch, input_embeds)
+        scores = self.score(hidden_states)
+
+        return self.pooler(scores, forward_batch)
+
+    def load_weights(self, weights: Iterable[Tuple[str, torch.Tensor]]):
+        stacked_params_mapping = [
+            # (param_name, shard_name, shard_id)
+            ("qkv_proj", "q_proj", "q"),
+            ("qkv_proj", "k_proj", "k"),
+            ("qkv_proj", "v_proj", "v"),
+            ("gate_up_proj", "gate_proj", 0),
+            ("gate_up_proj", "up_proj", 1),
+        ]
+        params_dict = dict(self.named_parameters())
+        for name, loaded_weight in weights:
+            for param_name, shard_name, shard_id in stacked_params_mapping:
+                if shard_name not in name:
+                    continue
+                name = name.replace(shard_name, param_name)
+                # Skip loading extra bias for GPTQ models.
+                if name.endswith(".bias") and name not in params_dict:
+                    continue
+                param = params_dict[name]
+                weight_loader = param.weight_loader
+                weight_loader(param, loaded_weight, shard_id)
+                break
+            else:
+                # lm_head is not used in vllm as it is tied with embed_token.
+                # To prevent errors, skip loading lm_head.weight.
+                if "lm_head.weight" in name:
+                    continue
+                # Skip loading extra bias for GPTQ models.
+                if name.endswith(".bias") and name not in params_dict:
+                    continue
+                param = params_dict[name]
+                weight_loader = getattr(param, "weight_loader", default_weight_loader)
+                weight_loader(param, loaded_weight)
+
+    def load_weights(self, weights: Iterable[Tuple[str, torch.Tensor]]):
+        Gemma2ForCausalLM.load_weights(self, weights)
+
+
+EntryClass = [Gemma2ForSequenceClassification]