Use configured threshold and exp. backoff for counter

gvanrossum · gvanrossum · commit 0f64231b8061 · 2023-12-12T18:55:46.000-08:00
diff --git a/Python/ceval.c b/Python/ceval.c
@@ -1106,11 +1106,15 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     }
 
     // Increment and check side exit counter.
+    // (Even though we only need it for certain opcodes.)
     next_instr = frame->instr_ptr;
     uint16_t *pcounter = current_executor->counters + pc;
-    *pcounter += 1;
-    if (*pcounter != 32 ||  // TODO: use resume_threshold
-        tstate->interp->optimizer == &_PyOptimizer_Default)
+    *pcounter += 1 << OPTIMIZER_BITS_IN_COUNTER;
+    /* We are using unsigned values, but we really want signed values, so
+     * do the 2s complement comparison manually */
+    uint16_t ucounter = *pcounter + (1 << 15);
+    uint16_t threshold = tstate->interp->optimizer_resume_threshold + (1 << 15);
+    if (ucounter <= threshold)
     {
         goto resume_frame;
     }
@@ -1160,6 +1164,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
                 jump_opcode = current_executor->trace[1].opcode;
             }
             if (jump_opcode != uopcode) {
+                *pcounter &= ((1 << OPTIMIZER_BITS_IN_COUNTER) - 1);
                 Py_INCREF(current_executor);
                 goto enter_tier_two;  // All systems go!
             }
@@ -1171,6 +1176,18 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
             // It will be decref'ed below.
         }
     }
+
+    // Exponential backoff if we didn't optimize.
+    int backoff = *pcounter & ((1 << OPTIMIZER_BITS_IN_COUNTER) - 1);
+    if (backoff < MINIMUM_TIER2_BACKOFF) {
+        backoff = MINIMUM_TIER2_BACKOFF;
+    }
+    else if (backoff < 15 - OPTIMIZER_BITS_IN_COUNTER) {
+        backoff++;
+    }
+    assert(backoff <= 15 - OPTIMIZER_BITS_IN_COUNTER);
+    *pcounter = ((1 << 16) - ((1 << OPTIMIZER_BITS_IN_COUNTER) << backoff)) | backoff;
+
     Py_DECREF(current_executor);
     goto resume_frame;
 }

Original file line number	Diff line number	Diff line change
`@@ -1106,11 +1106,15 @@ _PyEval_EvalFrameDefault(PyThreadState tstate, _PyInterpreterFrame frame, int`
`1106`	`1106`	`}`
`1107`	`1107`
`1108`	`1108`	`// Increment and check side exit counter.`
	`1109`	`+ // (Even though we only need it for certain opcodes.)`
`1109`	`1110`	`next_instr = frame->instr_ptr;`
`1110`	`1111`	`uint16_t *pcounter = current_executor->counters + pc;`
`1111`		`- *pcounter += 1;`
`1112`		`- if (*pcounter != 32 \|\| // TODO: use resume_threshold`
`1113`		`- tstate->interp->optimizer == &_PyOptimizer_Default)`
	`1112`	`+ *pcounter += 1 << OPTIMIZER_BITS_IN_COUNTER;`
	`1113`	`+ /* We are using unsigned values, but we really want signed values, so`
	`1114`	`+ * do the 2s complement comparison manually */`
	`1115`	`+ uint16_t ucounter = *pcounter + (1 << 15);`
	`1116`	`+ uint16_t threshold = tstate->interp->optimizer_resume_threshold + (1 << 15);`
	`1117`	`+ if (ucounter <= threshold)`
`1114`	`1118`	`{`
`1115`	`1119`	`goto resume_frame;`
`1116`	`1120`	`}`
`@@ -1160,6 +1164,7 @@ _PyEval_EvalFrameDefault(PyThreadState tstate, _PyInterpreterFrame frame, int`
`1160`	`1164`	`jump_opcode = current_executor->trace[1].opcode;`
`1161`	`1165`	`}`
`1162`	`1166`	`if (jump_opcode != uopcode) {`
	`1167`	`+ *pcounter &= ((1 << OPTIMIZER_BITS_IN_COUNTER) - 1);`
`1163`	`1168`	`Py_INCREF(current_executor);`
`1164`	`1169`	`goto enter_tier_two; // All systems go!`
`1165`	`1170`	`}`
`@@ -1171,6 +1176,18 @@ _PyEval_EvalFrameDefault(PyThreadState tstate, _PyInterpreterFrame frame, int`
`1171`	`1176`	`// It will be decref'ed below.`
`1172`	`1177`	`}`
`1173`	`1178`	`}`
	`1179`	`+`
	`1180`	`+ // Exponential backoff if we didn't optimize.`
	`1181`	`+ int backoff = *pcounter & ((1 << OPTIMIZER_BITS_IN_COUNTER) - 1);`
	`1182`	`+ if (backoff < MINIMUM_TIER2_BACKOFF) {`
	`1183`	`+ backoff = MINIMUM_TIER2_BACKOFF;`
	`1184`	`+ }`
	`1185`	`+ else if (backoff < 15 - OPTIMIZER_BITS_IN_COUNTER) {`
	`1186`	`+ backoff++;`
	`1187`	`+ }`
	`1188`	`+ assert(backoff <= 15 - OPTIMIZER_BITS_IN_COUNTER);`
	`1189`	`+ *pcounter = ((1 << 16) - ((1 << OPTIMIZER_BITS_IN_COUNTER) << backoff)) \| backoff;`
	`1190`	`+`
`1174`	`1191`	`Py_DECREF(current_executor);`
`1175`	`1192`	`goto resume_frame;`
`1176`	`1193`	`}`