[Bugfix] avoid warmup if text only expectation in multi_modal run (#40409)

Signed-off-by: khushali9 <khushali.desai9@gmail.com>

tests/renderers/test_warmup.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Unit tests for BaseRenderer.warmup MM-warmup behavior.
+
+These tests exercise:
+  - Zero-limit modalities are filtered from mm_counts passed to
+    get_dummy_processor_inputs (e.g. --limit-mm-per-prompt image=0 ...)
+  - MM warmup is skipped entirely when mm_processor is None
+
+No model weights are required: warmup() is called directly on a MagicMock
+that acts as the renderer instance.
+"""
+
+from unittest.mock import MagicMock, patch
+
+from vllm.renderers.base import BaseRenderer
+from vllm.renderers.params import ChatParams
+
+
+def _make_renderer_mock(mm_limits: dict[str, int]) -> MagicMock:
+    """Return a MagicMock that quacks like a BaseRenderer instance.
+
+    render_chat is mocked to raise ChatTemplateResolutionError so the chat
+    warmup block is skipped cleanly, keeping the test focused on MM warmup.
+    """
+    from vllm.entrypoints.chat_utils import ChatTemplateResolutionError
+
+    renderer = MagicMock()
+
+    # chat warmup: make render_chat raise so we skip past it cleanly
+    renderer.render_chat.side_effect = ChatTemplateResolutionError("no template")
+
+    # MM processor with configurable limits
+    mm_processor = MagicMock()
+    mm_processor.info.allowed_mm_limits = mm_limits
+    renderer.mm_processor = mm_processor
+
+    return renderer
+
+
+class TestMmWarmupZeroLimitFiltering:
+    """Zero-limit modalities must be excluded from mm_counts."""
+
+    def test_zero_limit_modality_excluded_from_mm_counts(self):
+        """A modality with limit=0 must not appear in mm_counts."""
+        renderer = _make_renderer_mock({"image": 1, "video": 0})
+
+        with patch("vllm.multimodal.processing.TimingContext", autospec=True):
+            BaseRenderer.warmup(renderer, ChatParams())
+
+        get_inputs = renderer.mm_processor.dummy_inputs.get_dummy_processor_inputs
+        get_inputs.assert_called_once()
+        _, kwargs = get_inputs.call_args
+        assert "video" not in kwargs["mm_counts"]
+        assert kwargs["mm_counts"]["image"] == 1
+
+    def test_all_zero_limits_passes_empty_mm_counts(self):
+        """When all limits are 0, mm_counts must be empty."""
+        renderer = _make_renderer_mock({"image": 0, "video": 0})
+
+        with patch("vllm.multimodal.processing.TimingContext", autospec=True):
+            BaseRenderer.warmup(renderer, ChatParams())
+
+        get_inputs = renderer.mm_processor.dummy_inputs.get_dummy_processor_inputs
+        get_inputs.assert_called_once()
+        _, kwargs = get_inputs.call_args
+        assert kwargs["mm_counts"] == {}
+
+    def test_positive_limits_all_included_in_mm_counts(self):
+        """All modalities with limit > 0 must be present in mm_counts."""
+        renderer = _make_renderer_mock({"image": 2, "video": 1})
+
+        with patch("vllm.multimodal.processing.TimingContext", autospec=True):
+            BaseRenderer.warmup(renderer, ChatParams())
+
+        get_inputs = renderer.mm_processor.dummy_inputs.get_dummy_processor_inputs
+        get_inputs.assert_called_once()
+        _, kwargs = get_inputs.call_args
+        assert kwargs["mm_counts"] == {"image": 1, "video": 1}
+
+
+class TestMmWarmupRunsNormally:
+    """MM warmup must run when mm_processor is set and limits > 0."""
+
+    def test_processor_apply_called(self):
+        renderer = _make_renderer_mock({"image": 1})
+
+        with patch("vllm.multimodal.processing.TimingContext", autospec=True):
+            BaseRenderer.warmup(renderer, ChatParams())
+
+        renderer.mm_processor.apply.assert_called_once()
+
+    def test_mm_cache_cleared_after_warmup(self):
+        renderer = _make_renderer_mock({"image": 1})
+
+        with patch("vllm.multimodal.processing.TimingContext", autospec=True):
+            BaseRenderer.warmup(renderer, ChatParams())
+
+        renderer.clear_mm_cache.assert_called_once()
+
+
+class TestMmWarmupSkippedWhenNoProcessor:
+    """MM warmup must be skipped when mm_processor is None (text-only model)."""
+
+    def test_no_warmup_without_processor(self):
+        renderer = _make_renderer_mock({})
+        renderer.mm_processor = None  # override to None
+
+        BaseRenderer.warmup(renderer, ChatParams())
+
+        renderer.model_config.get_multimodal_config.assert_not_called()

vllm/renderers/base.py

@@ -226,7 +226,9 @@ class BaseRenderer(ABC, Generic[_T]):
             model_config = self.model_config
             mm_config = model_config.get_multimodal_config()
             processor = self.mm_processor
-            mm_limits = processor.info.allowed_mm_limits
+            mm_limits = {
+                k: v for k, v in processor.info.allowed_mm_limits.items() if v > 0
+            }
 
             try:
                 logger.debug("Warming up multi-modal processing...")