feat: Enhance benchmark script with high priority and CPU affinity settings for stable measurements

Author: miskibin

tools/workers/benchmark_legal_moves.py

@@ -3,17 +3,64 @@
 
 import gc
 import json
+import os
 import sys
 import time
 from pathlib import Path
 from statistics import median
 
 
+def set_high_priority_and_affinity():
+    """Set high process priority and pin to a single CPU core for stable benchmarks."""
+    try:
+        import psutil
+        proc = psutil.Process()
+        
+        # Set high priority (below realtime, but above normal)
+        if sys.platform == "win32":
+            proc.nice(psutil.HIGH_PRIORITY_CLASS)
+        else:
+            # Unix: lower nice = higher priority, -10 is high but not root-only
+            try:
+                proc.nice(-10)
+            except PermissionError:
+                proc.nice(0)  # At least normal priority
+        
+        # Pin to first CPU core to avoid migration overhead
+        proc.cpu_affinity([0])
+        
+        return True
+    except ImportError:
+        # psutil not available, try platform-specific fallbacks
+        if sys.platform == "win32":
+            try:
+                import ctypes
+                # Set high priority
+                ctypes.windll.kernel32.SetPriorityClass(
+                    ctypes.windll.kernel32.GetCurrentProcess(), 
+                    0x00000080  # HIGH_PRIORITY_CLASS
+                )
+                # Set affinity to first core
+                ctypes.windll.kernel32.SetProcessAffinityMask(
+                    ctypes.windll.kernel32.GetCurrentProcess(),
+                    1  # First CPU core
+                )
+                return True
+            except Exception:
+                pass
+        return False
+    except Exception:
+        return False
+
+
 def main():
     positions_file = Path(sys.argv[1])
     warmup = int(sys.argv[2])
     rounds = int(sys.argv[3])
 
+    # Set high priority and CPU affinity for stable measurements
+    priority_set = set_high_priority_and_affinity()
+    
     positions = json.loads(positions_file.read_text())["positions"]
 
     from draughts import get_board
@@ -50,6 +97,7 @@ def main():
         "times": times,
         "median_ms": median(times) * 1000,
         "positions_count": len(clean_positions),
+        "high_priority": priority_set,
     }
     print(json.dumps(result))