[Fix] Adjust default chunked prefill size and cuda graph max bs accor…

…ding to GPU memory capacity (#2044)

python/sglang/srt/server_args.py

@@ -22,7 +22,12 @@
 import tempfile
 from typing import List, Optional
 
-from sglang.srt.utils import is_flashinfer_available, is_ipv6, is_port_available
+from sglang.srt.utils import (
+    get_gpu_memory_capacity,
+    is_flashinfer_available,
+    is_ipv6,
+    is_port_available,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -143,6 +148,9 @@ def __post_init__(self):
             # Disable chunked prefill
             self.chunked_prefill_size = None
 
+        if self.random_seed is None:
+            self.random_seed = random.randint(0, 1 << 30)
+
         # Mem fraction depends on the tensor parallelism size
         if self.mem_fraction_static is None:
             if self.tp_size >= 16:
@@ -156,8 +164,14 @@ def __post_init__(self):
             else:
                 self.mem_fraction_static = 0.88
 
-        if self.random_seed is None:
-            self.random_seed = random.randint(0, 1 << 30)
+        # Adjust for GPUs with small memory capacities
+        gpu_mem = get_gpu_memory_capacity()
+        if gpu_mem < 25000:
+            logger.warning(
+                "Automatically adjust --chunked-prefill-size for small GPUs."
+            )
+            self.chunked_prefill_size //= 4  # make it 2048
+            self.cuda_graph_max_bs = 4
 
         # Deprecation warnings
         if self.disable_flashinfer:

python/sglang/srt/utils.py

@@ -27,6 +27,7 @@
 import shutil
 import signal
 import socket
+import subprocess
 import tempfile
 import time
 import warnings
@@ -791,3 +792,35 @@ def add_prometheus_middleware(app):
     # Workaround for 307 Redirect for /metrics
     metrics_route.path_regex = re.compile("^/metrics(?P<path>.*)$")
     app.routes.append(metrics_route)
+
+
+def get_gpu_memory_capacity():
+    try:
+        # Run nvidia-smi and capture the output
+        result = subprocess.run(
+            ["nvidia-smi", "--query-gpu=memory.total", "--format=csv,noheader,nounits"],
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            text=True,
+        )
+
+        if result.returncode != 0:
+            raise RuntimeError(f"nvidia-smi error: {result.stderr.strip()}")
+
+        # Parse the output to extract memory values
+        memory_values = [
+            float(mem)
+            for mem in result.stdout.strip().split("\n")
+            if re.match(r"^\d+(\.\d+)?$", mem.strip())
+        ]
+
+        if not memory_values:
+            raise ValueError("No GPU memory values found.")
+
+        # Return the minimum memory value
+        return min(memory_values)
+
+    except FileNotFoundError:
+        raise RuntimeError(
+            "nvidia-smi not found. Ensure NVIDIA drivers are installed and accessible."
+        )