[Core] Subclass ModelRunner to support cross-attention & encoder sequ…

…ences (towards eventual encoder/decoder model support) (vllm-project#4942)

Co-authored-by: Andrew Feldman <afeld2012@gmail.com>
Co-authored-by: Nick Hill <nickhill@us.ibm.com>

.buildkite/test-pipeline.yaml

@@ -148,8 +148,9 @@ steps:
     - python3 cpu_offload.py
     - python3 offline_inference_with_prefix.py
     - python3 llm_engine_example.py
-    - python3 llava_example.py
+    - python3 offline_inference_vision_language.py
     - python3 tensorize_vllm_model.py --model facebook/opt-125m serialize --serialized-directory /tmp/ --suffix v1 && python3 tensorize_vllm_model.py --model facebook/opt-125m deserialize --path-to-tensors /tmp/vllm/facebook/opt-125m/v1/model.tensors
+    - python3 offline_inference_encoder_decoder.py
 
 - label: Models Test # 1hr10min
   source_file_dependencies:
@@ -289,6 +290,7 @@ steps:
   commands:
   - VLLM_TEST_SAME_HOST=1 torchrun --nproc-per-node=4 distributed/test_same_node.py
   - TARGET_TEST_SUITE=L4 pytest -v -s distributed/test_basic_distributed_correctness.py
+  - pytest -v -s distributed/test_basic_distributed_correctness_enc_dec.py
   - pytest -v -s distributed/test_chunked_prefill_distributed.py
   - pytest -v -s distributed/test_multimodal_broadcast.py
   - pytest -v -s spec_decode/e2e/test_integration_dist_tp2.py

examples/offline_inference_encoder_decoder.py

@@ -0,0 +1,99 @@
+'''
+Demonstrate prompting of text-to-text
+encoder/decoder models, specifically BART
+'''
+
+from vllm import LLM, SamplingParams
+from vllm.inputs import ExplicitEncoderDecoderPrompt, TextPrompt, TokensPrompt
+from vllm.utils import zip_enc_dec_prompt_lists
+
+dtype = "float"
+
+# Create a BART encoder/decoder model instance
+llm = LLM(
+    model="facebook/bart-large-cnn",
+    dtype=dtype,
+)
+
+# Get BART tokenizer
+tokenizer = llm.llm_engine.get_tokenizer_group()
+
+# Test prompts
+#
+# This section shows all of the valid ways to prompt an
+# encoder/decoder model.
+#
+# - Helpers for building prompts
+text_prompt_raw = "Hello, my name is"
+text_prompt = TextPrompt(prompt="The president of the United States is")
+tokens_prompt = TokensPrompt(prompt_token_ids=tokenizer.encode(
+    prompt="The capital of France is"))
+# - Pass a single prompt to encoder/decoder model
+#   (implicitly encoder input prompt);
+#   decoder input prompt is assumed to be None
+
+single_text_prompt_raw = text_prompt_raw  # Pass a string directly
+single_text_prompt = text_prompt  # Pass a TextPrompt
+single_tokens_prompt = tokens_prompt  # Pass a TokensPrompt
+
+# - Pass explicit encoder and decoder input prompts within one data structure.
+#   Encoder and decoder prompts can both independently be text or tokens, with
+#   no requirement that they be the same prompt type. Some example prompt-type
+#   combinations are shown below, note that these are not exhaustive.
+
+enc_dec_prompt1 = ExplicitEncoderDecoderPrompt(
+    # Pass encoder prompt string directly, &
+    # pass decoder prompt tokens
+    encoder_prompt=single_text_prompt_raw,
+    decoder_prompt=single_tokens_prompt,
+)
+enc_dec_prompt2 = ExplicitEncoderDecoderPrompt(
+    # Pass TextPrompt to encoder, and
+    # pass decoder prompt string directly
+    encoder_prompt=single_text_prompt,
+    decoder_prompt=single_text_prompt_raw,
+)
+enc_dec_prompt3 = ExplicitEncoderDecoderPrompt(
+    # Pass encoder prompt tokens directly, and
+    # pass TextPrompt to decoder
+    encoder_prompt=single_tokens_prompt,
+    decoder_prompt=single_text_prompt,
+)
+
+# - Finally, here's a useful helper function for zipping encoder and
+#   decoder prompt lists together into a list of ExplicitEncoderDecoderPrompt
+#   instances
+zipped_prompt_list = zip_enc_dec_prompt_lists(
+    ['An encoder prompt', 'Another encoder prompt'],
+    ['A decoder prompt', 'Another decoder prompt'])
+
+# - Let's put all of the above example prompts together into one list
+#   which we will pass to the encoder/decoder LLM.
+prompts = [
+    single_text_prompt_raw, single_text_prompt, single_tokens_prompt,
+    enc_dec_prompt1, enc_dec_prompt2, enc_dec_prompt3
+] + zipped_prompt_list
+
+print(prompts)
+
+# Create a sampling params object.
+sampling_params = SamplingParams(
+    temperature=0,
+    top_p=1.0,
+    min_tokens=0,
+    max_tokens=20,
+)
+
+# Generate output tokens from the prompts. The output is a list of
+# RequestOutput objects that contain the prompt, generated
+# text, and other information.
+outputs = llm.generate(prompts, sampling_params)
+
+# Print the outputs.
+for output in outputs:
+    prompt = output.prompt
+    encoder_prompt = output.encoder_prompt
+    generated_text = output.outputs[0].text
+    print(f"Encoder prompt: {encoder_prompt!r}, "
+          f"Decoder prompt: {prompt!r}, "
+          f"Generated text: {generated_text!r}")