[TPU][V1] Disable per-request seed/Generator (#16172)

Signed-off-by: NickLucche <nlucches@redhat.com>

tests/v1/tpu/test_sampler.py

@@ -34,3 +34,8 @@ def test_sampler_different(model_name: str):
     sampling_params = SamplingParams(temperature=0.1, min_p=0.8, max_tokens=64)
     output2 = llm.generate(prompts, sampling_params)
     assert output[0].outputs[0].text != output2[0].outputs[0].text
+
+    with pytest.raises(ValueError):
+        # Unsupported `seed` param.
+        sampling_params = SamplingParams(temperature=0.3, seed=42)
+        output2 = llm.generate(prompts, sampling_params)

vllm/platforms/tpu.py

@@ -7,7 +7,7 @@ import torch
 import vllm.envs as envs
 from vllm.inputs import PromptType
 from vllm.logger import init_logger
-from vllm.sampling_params import SamplingParams
+from vllm.sampling_params import SamplingParams, SamplingType
 
 from .interface import Platform, PlatformEnum, _Backend
 
@@ -145,7 +145,10 @@ class TpuPlatform(Platform):
         params: Union[SamplingParams, PoolingParams],
     ) -> None:
         """Raises if this request is unsupported on this platform"""
-        if isinstance(params,
-                      SamplingParams) and params.guided_decoding is not None:
+        if isinstance(params, SamplingParams):
+            if params.guided_decoding is not None:
                 raise ValueError("Structured output is not supported on "
                                  f"{cls.device_name}.")
+            if params.sampling_type == SamplingType.RANDOM_SEED:
+                raise ValueError(
+                    "Torch XLA does not support per-request seed.")

vllm/v1/sample/tpu/metadata.py

@@ -33,10 +33,6 @@ class TPUSupportedSamplingMetadata:
     # Greedy sampling flag for compiling single xla graph.
     all_greedy: bool = True
 
-    # Generator not supported by xla
-    generators: dict[int,
-                     torch.Generator] = field(default_factory=lambda: dict())
-
     # unsupported, you need to return an extra tensor of static size BxV
     max_num_logprobs = None
 
@@ -57,6 +53,15 @@ class TPUSupportedSamplingMetadata:
     allowed_token_ids_mask = None
     bad_words_token_ids = None
 
+    # Generator not supported by xla
+    _generators: dict[int,
+                      torch.Generator] = field(default_factory=lambda: dict())
+
+    @property
+    def generators(self) -> dict[int, torch.Generator]:
+        # Generator not supported by torch/xla. This field must be immutable.
+        return self._generators
+
     @classmethod
     def from_input_batch(
         cls,
@@ -109,5 +114,4 @@ class TPUSupportedSamplingMetadata:
             top_p=None,  # input_batch.top_p[:padded_num_reqs],
             top_k=None,  # input_batch.top_k[:padded_num_reqs],
             min_p=input_batch.min_p_cpu_tensor[:padded_num_reqs].to(
-                xla_device),
-            generators=input_batch.generators)
+                xla_device))

vllm/v1/worker/tpu_model_runner.py

@@ -23,7 +23,6 @@ from vllm.model_executor.model_loader import get_model
 from vllm.multimodal import MULTIMODAL_REGISTRY
 from vllm.multimodal.inputs import MultiModalKwargs, PlaceholderRange
 from vllm.multimodal.utils import group_mm_inputs_by_modality
-from vllm.sampling_params import SamplingType
 from vllm.sequence import IntermediateTensors
 from vllm.utils import LayerBlockType, cdiv, is_pin_memory_available
 from vllm.v1.attention.backends.pallas import (PallasAttentionBackend,
@@ -267,11 +266,6 @@ class TPUModelRunner:
         for new_req_data in scheduler_output.scheduled_new_reqs:
             req_id = new_req_data.req_id
             sampling_params = new_req_data.sampling_params
-            if sampling_params.sampling_type == SamplingType.RANDOM_SEED:
-                generator = torch.Generator(device=self.device)
-                generator.manual_seed(sampling_params.seed)
-            else:
-                generator = None
 
             self.requests[req_id] = CachedRequestState(
                 req_id=req_id,
@@ -280,7 +274,7 @@ class TPUModelRunner:
                 mm_inputs=new_req_data.mm_inputs,
                 mm_positions=new_req_data.mm_positions,
                 sampling_params=sampling_params,
-                generator=generator,
+                generator=None,
                 block_ids=new_req_data.block_ids,
                 num_computed_tokens=new_req_data.num_computed_tokens,
                 output_token_ids=[],