Merge pull request #3841 from unslothai/fix-vllm-pdl-blackwell

Fix vLLM PDL bug on Blackwell GPUs (B200/B100)

unsloth/__init__.py

@@ -126,6 +126,7 @@ from .import_fixes import (
     fix_xformers_performance_issue,
     fix_vllm_aimv2_issue,
     fix_vllm_guided_decoding_params,
+    fix_vllm_pdl_blackwell,
     ignore_logger_messages,
     patch_ipykernel_hf_xet,
     patch_trackio,
@@ -138,6 +139,7 @@ from .import_fixes import (
 fix_xformers_performance_issue()
 fix_vllm_aimv2_issue()
 fix_vllm_guided_decoding_params()
+fix_vllm_pdl_blackwell()
 ignore_logger_messages()
 patch_ipykernel_hf_xet()
 patch_trackio()
@@ -149,6 +151,7 @@ fix_executorch()
 del fix_xformers_performance_issue
 del fix_vllm_aimv2_issue
 del fix_vllm_guided_decoding_params
+del fix_vllm_pdl_blackwell
 del ignore_logger_messages
 del patch_ipykernel_hf_xet
 del patch_trackio

unsloth/import_fixes.py

@@ -556,3 +556,144 @@ def fix_huggingface_hub():
         huggingface_hub.is_offline_mode = (
             lambda: huggingface_hub.constants.HF_HUB_OFFLINE
         )
+
+
+def fix_vllm_pdl_blackwell():
+    """
+    Fix vLLM PDL (Programmatic Dependent Launch) bug on Blackwell GPUs (SM100).
+
+    The issue: vLLM's LoRA Triton kernels use tl.extra.cuda.gdc_wait() for PDL
+    optimization on SM90+ GPUs. This fails on SM100 (B200/B100) during CUDA graph
+    capture because Triton's pipeliner can't handle gdc_wait in complex kernels.
+
+    See: https://github.com/vllm-project/vllm/issues/30872
+    """
+    if importlib.util.find_spec("vllm") is None:
+        return
+
+    # Check if any CUDA GPU is SM100 (Blackwell)
+    try:
+        import torch
+
+        if not torch.cuda.is_available():
+            return
+
+        # Scan all GPUs for SM100 - fix applies globally via env var and monkey-patch
+        has_sm100 = False
+        sm100_gpu_name = None
+        for i in range(torch.cuda.device_count()):
+            major, minor = torch.cuda.get_device_capability(i)
+            if major == 10:
+                has_sm100 = True
+                sm100_gpu_name = torch.cuda.get_device_name(i)
+                break
+
+        if not has_sm100:
+            return
+    except Exception:
+        return
+
+    # Helper to check if module spec exists
+    def _spec_exists(name):
+        try:
+            return importlib.util.find_spec(name) is not None
+        except (ModuleNotFoundError, ValueError):
+            return False
+
+    # Check if vLLM has the PDL-related modules before doing internet check
+    has_utils = _spec_exists("vllm.lora.ops.triton_ops.utils")
+    has_expand_op = _spec_exists("vllm.lora.ops.triton_ops.lora_expand_op")
+    has_shrink_op = _spec_exists("vllm.lora.ops.triton_ops.lora_shrink_op")
+
+    if not has_utils and not has_expand_op and not has_shrink_op:
+        # Old vLLM version without PDL support - nothing to patch
+        return
+
+    # Check if GitHub issue is closed (fix merged upstream)
+    issue_closed = False
+    try:
+        import socket
+        import urllib.request
+        import json as json_module
+
+        # Quick internet connectivity check (0.5s timeout)
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        sock.settimeout(0.5)
+        try:
+            sock.connect(("api.github.com", 443))
+            has_internet = True
+        except (socket.timeout, OSError):
+            has_internet = False
+        finally:
+            sock.close()
+
+        if has_internet:
+            api_url = "https://api.github.com/repos/vllm-project/vllm/issues/30872"
+            req = urllib.request.Request(
+                api_url,
+                headers = {
+                    "User-Agent": "Unsloth-PDL-Fix",
+                    "Accept": "application/vnd.github.v3+json",
+                },
+            )
+            with urllib.request.urlopen(req, timeout = 3) as response:
+                data = json_module.loads(response.read().decode())
+                issue_closed = data.get("state") == "closed"
+    except Exception:
+        # If we can't check, assume issue is still open (apply fix to be safe)
+        pass
+
+    if issue_closed:
+        logger.info(
+            f"Unsloth: SM100 ({sm100_gpu_name}) detected but PDL issue #30872 "
+            f"is closed - skipping PDL fix"
+        )
+        return
+
+    # Apply the PDL fix
+    os.environ["TRITON_DISABLE_PDL"] = "1"
+
+    def fake_supports_pdl(*args, **kwargs):
+        return False
+
+    patched = []
+
+    # First, patch the source module (utils.py) where supports_pdl is defined.
+    # This is critical because supports_pdl uses @lru_cache - we must clear the
+    # cache to prevent stale cached results from the original function.
+    try:
+        utils_module = importlib.import_module("vllm.lora.ops.triton_ops.utils")
+        if hasattr(utils_module, "supports_pdl"):
+            original_fn = utils_module.supports_pdl
+            if hasattr(original_fn, "cache_clear"):
+                original_fn.cache_clear()
+            utils_module.supports_pdl = fake_supports_pdl
+            patched.append("utils")
+    except (ImportError, ModuleNotFoundError, AttributeError):
+        pass
+
+    # Also patch the consumer modules that import supports_pdl from utils.
+    # This ensures the patched function is used even if the module was already
+    # imported before this fix runs.
+    consumer_modules = {
+        "lora_expand_op": "vllm.lora.ops.triton_ops.lora_expand_op",
+        "lora_shrink_op": "vllm.lora.ops.triton_ops.lora_shrink_op",
+        "fused_moe_lora_op": "vllm.lora.ops.triton_ops.fused_moe_lora_op",
+    }
+    for name, path in consumer_modules.items():
+        try:
+            module = importlib.import_module(path)
+            if hasattr(module, "supports_pdl"):
+                module.supports_pdl = fake_supports_pdl
+                patched.append(name)
+        except (ImportError, ModuleNotFoundError, AttributeError):
+            pass
+
+    if patched:
+        logger.info(
+            f"Unsloth: Applied PDL fix for SM100 ({sm100_gpu_name}) - "
+            f"patched: {', '.join(patched)}"
+        )
+    else:
+        # Just set the env var - vLLM might be an older version without supports_pdl
+        logger.info(f"Unsloth: Set TRITON_DISABLE_PDL=1 for SM100 ({sm100_gpu_name})")