feat: Add --enable-log-outputs flag for logging model generations #20707
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Summary of Changes
Hello @mizadri, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request introduces a new, optional --enable-log-outputs command-line flag to vLLM, enabling comprehensive logging of model generations. This feature complements the existing input logging by providing detailed output information, which is crucial for debugging, monitoring, auditing, and development workflows. It supports various response types, including streaming deltas, complete responses, and tool calls, while ensuring full backward compatibility and minimal performance impact.
Highlights
- New Output Logging Flag: A new
--enable-log-outputsCLI flag has been added to enable comprehensive logging of model generations (outputs), disabled by default for backward compatibility. - Comprehensive Output Logging: The system now logs model outputs for both streaming (individual token deltas and final complete responses) and non-streaming requests, including support for tool calls and their arguments.
- Integration with Existing Logging: The new output logging functionality integrates seamlessly with the existing
RequestLoggerand respects the--max-log-lensetting for truncation of long outputs and token ID lists. - API Endpoint Coverage: Output logging has been implemented for both
/v1/chat/completions(streaming and non-streaming) and/v1/responsesendpoints, ensuring broad applicability.
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Code Review
This pull request introduces an --enable-log-outputs flag to enable logging of model generations, complementing vLLM's existing input logging. The changes include modifications to RequestLogger, CLI arguments, and enhancements to OpenAIServingChat and OpenAIServingResponses. The new unit tests for the logger are not correctly validating the behavior, and there are a couple of suggestions to enhance the logging functionality.
tests/test_logger.py
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The assertions in this test, and all subsequent new tests for log_outputs, are asserting against the wrong argument indices from the mocked logger call. This means the tests are not correctly validating the intended behavior and are likely passing incorrectly.
For example, call_args[0] is asserted to be the outputs string, but it's actually the format string. The outputs argument is at index 3.
The arguments passed to logger.info are (format_string, request_id, stream_info, outputs, output_token_ids, finish_reason). The assertions need to be updated to check the arguments at their correct positions.
This issue is present in:
test_request_logger_log_outputstest_request_logger_log_outputs_streaming_deltatest_request_logger_log_outputs_streaming_completetest_request_logger_log_outputs_with_truncationtest_request_logger_log_outputs_none_valuestest_request_logger_log_outputs_empty_output
mock_logger.info.assert_called_once()
call_args = mock_logger.info.call_args.args
# logger.info(format_string, request_id, stream_info, outputs, output_token_ids, finish_reason)
assert "Generated response %s%s" in call_args[0]
assert call_args[1] == "test-123"
assert call_args[3] == "Hello, world!"
assert call_args[4] == [1, 2, 3, 4]
assert call_args[5] == "stop"There was a problem hiding this comment.
The log message for a completed streaming response currently only includes the number of generated tokens, not the full concatenated text of the response. This doesn't align with the goal of "comprehensive output logging" mentioned in the PR description and reduces the utility of these logs for debugging and auditing.
The comment // For now, we'll log the completion tokens count as final output indicates this might be a known limitation.
To make this more useful, I recommend accumulating the full response text from the streaming deltas and logging it here. This would provide a complete record of the generated output. You might be able to use or adapt the previous_texts variable for this purpose, though you'd need to ensure it's populated even when tools are not in use.
for i in range(num_choices):
full_text = (previous_texts[i] if previous_texts
and i < len(previous_texts) else
f"<streaming_complete: {previous_num_tokens[i]} tokens>"
)
self.request_logger.log_outputs(
request_id=request_id,
outputs=full_text,
output_token_ids=None, # Consider also logging all token IDs
finish_reason="streaming_complete",
is_streaming=True,
delta=False,
)There was a problem hiding this comment.
The logic for extracting delta_content from tool calls only considers the first tool call in a delta message (delta_message.tool_calls[0]). While a delta typically contains a single tool call, the tool_calls attribute is a list, suggesting multiple could be present. If a delta ever contains more than one tool call, the arguments from subsequent tool calls will not be logged.
To make this more robust, I suggest iterating through all items in delta_message.tool_calls to ensure all arguments are captured.
if delta_message.content:
delta_content = delta_message.content
elif delta_message.tool_calls:
delta_content = "".join(
tc.function.arguments
for tc in delta_message.tool_calls
if tc.function and tc.function.arguments)
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Thanks for contributing! Can you resolve the pre-commit issues? |
mizadri
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Add optional output logging functionality to complement existing input logging. By default, vLLM only logs incoming requests but not model outputs. This feature adds comprehensive output logging controlled by a new CLI flag. Key features: - New --enable-log-outputs CLI flag (disabled by default) - Logs both streaming and non-streaming responses - Supports individual token deltas in streaming mode - Handles tool calls and function arguments - Respects existing --max-log-len truncation settings - Maintains full backward compatibility Implementation: - Added RequestLogger.log_outputs() method for output logging - Enhanced OpenAIServingChat with output logging in both generators - Enhanced OpenAIServingResponses with output logging support - Added comprehensive test coverage for all scenarios Usage: python -m vllm.entrypoints.openai.api_server --model MODEL_NAME --enable-log-outputs Docker: docker run --gpus all -p 8000:8000 vllm/vllm-openai:latest --model MODEL_NAME --enable-log-outputs This addresses the common need for debugging and monitoring model outputs while preserving the existing behavior by default. Signed-off-by: Adrian Garcia <[email protected]>
Fix type annotation and variable naming issues identified by mypy: - Change output_token_ids parameter type from list[int] to Sequence[int] to handle compatibility with different sequence types from output objects - Fix variable naming conflict in tool call logging (tool_call_info -> tool_call_descriptions) - Add proper type conversion in log_outputs method for truncation - Update test imports to include Sequence type These fixes ensure the output logging feature passes mypy type checking while maintaining full functionality and backward compatibility. Signed-off-by: Adrian Garcia <[email protected]>
- Break long conditional expressions into multiple lines - Fix tool call logging lines exceeding 80 characters - Remove trailing whitespace - Maintain code readability and functionality Signed-off-by: Adrian Garcia <[email protected]>
Shorten comment from 81 to 71 characters to comply with E501 line length limit. The comment 'Log individual streaming delta if output logging is enabled' was shortened to 'Log streaming delta if output logging is enabled' while maintaining clarity and meaning. Signed-off-by: Adrian Garcia <[email protected]>
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I tried to fix the issues mentioned, but I am not sure why the pre commit hooks are failing now |
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It looks like the code is not formatted properly. You should install the pre-commit hook and run it locally before committing and pushing them to remote |
Signed-off-by: Adrian Garcia <[email protected]>
Signed-off-by: Adrian Garcia <[email protected]>
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Hey there @DarkLight1337 I addressed the formatting changes but in my last commit there was a fail during the Lint and Deploy charts, it appears to be an issue related to Triton, It does not seem to be related to my changes. The job failed because tl.int32 does not exist in the Triton installation; Not sure if we need to use tl.int64 or upgrade the triton package. |
The assertions in log_outputs test methods were checking wrong argument
indices from mocked logger calls, causing tests to validate incorrect
behavior and pass incorrectly.
The logger.info call signature is:
logger.info(format_string, request_id, stream_info, outputs,
output_token_ids, finish_reason)
Fixed argument index assertions in all affected test methods:
- test_request_logger_log_outputs
- test_request_logger_log_outputs_streaming_delta
- test_request_logger_log_outputs_streaming_complete
- test_request_logger_log_outputs_with_truncation
- test_request_logger_log_outputs_none_values
- test_request_logger_log_outputs_empty_output
- test_request_logger_log_outputs_integration
Tests now correctly validate outputs at index 3, output_token_ids at
index 4, and finish_reason at index 5, instead of the previous
incorrect indices 1, 2, and 3 respectively.
Signed-off-by: Adrian Garcia <[email protected]>
Previously, the log message for a completed streaming response only included the number of generated tokens, which limited debugging and auditing capabilities. This change: - Modifies the streaming response logging to include the full concatenated text instead of just token counts - Adds test coverage to verify the full text logging behavior - Ensures all logger.info call argument indices are correct in tests The change improves the utility of logs for debugging and auditing by providing complete output records. Signed-off-by: Adrian Garcia <[email protected]>
Previously only the first tool call’s arguments were captured when logging streaming delta content, which could miss information if multiple tool calls were present in a single delta. The extraction logic now concatenates the arguments from *all* tool calls ensuring complete logging. Additional changes: * Updated unit tests to remain within Ruff line-length limits (E501). * Auto-formatted touched files via project pre-commit hooks. Signed-off-by: Adrian Garcia <[email protected]>
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This pull request has merge conflicts that must be resolved before it can be |
Resolved merge conflicts in vllm/entrypoints/openai/api_server.py while preserving logger enhancements and SSE decoding added in this branch. All logger tests pass. Signed-off-by: Adrian Garcia <[email protected]>
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Solved all merge conflicts and brought latest changes from main |
tests/test_logger.py
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| mock_logger.info.assert_called_once() | ||
| call_args = mock_logger.info.call_args.args | ||
| # logger.info(format_string, request_id, stream_info, outputs, output_token_ids, finish_reason) |
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Please remove the commented-out code
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…lm-project#20707) Signed-off-by: Adrian Garcia <[email protected]> Signed-off-by: Paul Pak <[email protected]>
…lm-project#20707) Signed-off-by: Adrian Garcia <[email protected]> Signed-off-by: Diego-Castan <[email protected]>
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@mizadri Hi! Thanks for this wonderful feature, but I tried to use it with pip install from source and did not see any output logs, did I miss anything here? logs from server: |
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I also can't use the --enable-log-outputs flag, in the latest vllm version 0.10.1.1. NO output log is printed. below is my server log, maybe can help you. @DarkLight1337 [api_server.py:1805] vLLM API server version 0.10.1.1
non-default args: {'model_tag': 'qwen3', 'port': 8192, 'enable_auto_tool_choice': True, 'tool_call_parser': 'hermes',
'enable_log_outputs': True,
'model': 'qwen3', 'served_model_name': ['qwen3'], 'load_format': 'sharded_state', 'reasoning_parser': 'qwen3', 'tensor_parallel_size': 8, 'gpu_memory_utilization': 0.95, 'enable_prefix_caching': True, 'enable_log_requests': True} |
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@FlyCarrot @DarkLight1337 I got the same issue. I think the problem is that this flag is only available in serving_chat entrypoint. If you have |
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You're welcome to fix this, thanks! |
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@DarkLight1337 submitted a PR #23634 |
…lm-project#20707) Signed-off-by: Adrian Garcia <[email protected]>
…lm-project#20707) Signed-off-by: Adrian Garcia <[email protected]> Signed-off-by: Xiao Yu <[email protected]>
…lm-project#20707) Signed-off-by: Adrian Garcia <[email protected]>
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Response Logs: I am still not getting generation response in my logs. |
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I don't think this PR has made it to a release yet, so please wait until v0.10.2 or install the nightly wheel |
There are no fixed records of - enable log output in v0.10.2 version |
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Do you mean that the flag is undocumented, or does it not work at all? |
There is no record in the flag, but I just updated v0.10.2 and this version is working. Thanks. |
thank you. |
| else: | ||
| # Update for comprehensive logging even in simple case | ||
| assert previous_texts is not None | ||
| previous_texts[i] += delta_text |
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When Stream=True, this line causes an error by repeatedly accumulating the previous content.
10 participants
Add --enable-log-outputs flag for logging model generations
📋 Summary
This PR adds optional output logging functionality to complement vLLM's existing input logging. By default, vLLM logs incoming requests (prompts, parameters, token IDs) but does not log model outputs. This feature adds comprehensive output logging controlled by a new CLI flag.
🚀 Motivation
✨ Key Features
--enable-log-outputsCLI flag (disabled by default for backward compatibility)--max-log-lensettings/v1/chat/completionsand/v1/responses🔧 Implementation
Components Added/Modified:
RequestLogger.log_outputs()method (vllm/entrypoints/logger.py)CLI argument (
vllm/entrypoints/openai/cli_args.py)--enable-log-outputsflag with help textOpenAIServingChat enhancements (
vllm/entrypoints/openai/serving_chat.py)chat_completion_stream_generator()for streamingchat_completion_full_generator()for non-streamingOpenAIServingResponses enhancements (
vllm/entrypoints/openai/serving_responses.py)responses_full_generator()methodServer initialization (
vllm/entrypoints/openai/api_server.py)enable_log_outputsflag to serving classesComprehensive tests (
tests/test_logger.py)🧪 Testing
Manual Testing Performed:
--max-log-lenAutomated Tests:
log_outputs()methodlog_inputs()📝 Usage Examples
Command Line:
Docker:
Environment Variables (SageMaker style):
export SM_VLLM_ENABLE_LOG_OUTPUTS=true🔍 Log Output Examples
Input Logging (existing, always active):
Output Logging (NEW, with --enable-log-outputs):
Streaming Delta Logging (NEW):
🔄 Backward Compatibility
--enable-log-outputs📊 Performance Impact
🔐 Security Considerations
🎯 Future Enhancements (Out of Scope)
📋 Checklist
🤝 Related Issues
This addresses common requests for output logging capability that have appeared in:
📸 Screenshots/Demo
// Does not let me attach screenshot
Successfully tested with DialoGPT-small model showing:
Ready for review! This feature provides a much-requested capability while maintaining full backward compatibility and following vLLM's existing patterns.