diff options
Diffstat (limited to 'Python/ceval.c')
| -rw-r--r-- | Python/ceval.c | 24 |
1 files changed, 13 insertions, 11 deletions
diff --git a/Python/ceval.c b/Python/ceval.c index ec279bf..c75caf6 100644 --- a/Python/ceval.c +++ b/Python/ceval.c @@ -617,18 +617,20 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag) COMPARE_OP is often followed by JUMP_IF_FALSE or JUMP_IF_TRUE. And, those opcodes are often followed by a POP_TOP. - Verifying the prediction costs a single high-speed test of register + Verifying the prediction costs a single high-speed test of a register variable against a constant. If the pairing was good, then the - processor has a high likelihood of making its own successful branch - prediction which results in a nearly zero overhead transition to the - next opcode. - - A successful prediction saves a trip through the eval-loop including - its two unpredictable branches, the HAS_ARG test and the switch-case. - - If collecting opcode statistics, turn off prediction so that - statistics are accurately maintained (the predictions bypass - the opcode frequency counter updates). + processor's own internal branch predication has a high likelihood of + success, resulting in a nearly zero-overhead transition to the + next opcode. A successful prediction saves a trip through the eval-loop + including its two unpredictable branches, the HAS_ARG test and the + switch-case. Combined with the processor's internal branch prediction, + a successful PREDICT has the effect of making the two opcodes run as if + they were a single new opcode with the bodies combined. + + If collecting opcode statistics, your choices are to either keep the + predictions turned-on and interpret the results as if some opcodes + had been combined or turn-off predictions so that the opcode frequency + counter updates for both opcodes. */ #ifdef DYNAMIC_EXECUTION_PROFILE |