optimize some constants

Author: cocolato

Include/internal/pycore_optimizer.h

@@ -18,18 +18,19 @@ extern "C" {
 /* Default fitness configuration values for trace quality control.
  * FITNESS_INITIAL and FITNESS_INITIAL_SIDE can be overridden via
  * PYTHON_JIT_FITNESS_INITIAL and PYTHON_JIT_FITNESS_INITIAL_SIDE */
-#define FITNESS_PER_INSTRUCTION        2
-#define FITNESS_INITIAL             2000
-#define FITNESS_INITIAL_SIDE         800
-#define FITNESS_BRANCH_BASE            5
-#define FITNESS_BACKWARD_EDGE         80
+#define FITNESS_PER_INSTRUCTION     2
+#define FITNESS_BRANCH_BASE         5
+#define FITNESS_INITIAL             (FITNESS_PER_INSTRUCTION * 1000)
+#define FITNESS_INITIAL_SIDE        (FITNESS_INITIAL / 2)
+#define FITNESS_BACKWARD_EDGE       (FITNESS_PER_INSTRUCTION / 10)
 
 /* Exit quality constants for fitness-based trace termination.
  * Higher values mean better places to stop the trace. */
-#define EXIT_QUALITY_CLOSE_LOOP      800
-#define EXIT_QUALITY_ENTER_EXECUTOR  500
+
 #define EXIT_QUALITY_DEFAULT         200
-#define EXIT_QUALITY_SPECIALIZABLE    50
+#define EXIT_QUALITY_CLOSE_LOOP      (4 * EXIT_QUALITY_DEFAULT)
+#define EXIT_QUALITY_ENTER_EXECUTOR  (2 * EXIT_QUALITY_DEFAULT + 100)
+#define EXIT_QUALITY_SPECIALIZABLE   (EXIT_QUALITY_DEFAULT / 4)
 
 
 typedef struct _PyJitUopBuffer {

Python/optimizer.c

@@ -605,9 +605,10 @@ compute_branch_penalty(uint16_t history, bool branch_taken)
     int taken_count = _Py_popcount32((uint32_t)history);
     int on_trace_count = branch_taken ? taken_count : 16 - taken_count;
     int off_trace = 16 - on_trace_count;
-    /* Quadratic scaling: off_trace^2 ranges from 0 (fully biased our way)
-     * to 256 (fully biased against us, e.g. 15/16 left but traced right). */
-    return FITNESS_BRANCH_BASE + off_trace * off_trace;
+    /* Linear scaling: off_trace ranges from 0 (fully biased our way)
+     * to 16 (fully biased against us), so the penalty ranges from
+     * FITNESS_BRANCH_BASE to FITNESS_BRANCH_BASE + 48. */
+    return FITNESS_BRANCH_BASE + off_trace * 2;
 }
 
 /* Compute exit quality for the current trace position.