Done: http://bugs.python.org/issue4477 On Sun, Nov 30, 2008 at 8:14 PM, Brett Cannon <brett@python.org> wrote:
Can you toss the patch into the issue tracker, Jeffrey, so that any patch comments can be done there?
-Brett
On Sun, Nov 30, 2008 at 17:54, Jeffrey Yasskin <jyasskin@gmail.com> wrote:
Tracing support shows up fairly heavily an a Python profile, even though it's nearly always turned off. The attached patch against the trunk speeds up PyBench by 2% for me. All tests pass. I have 2 questions:
1) Can other people corroborate this speedup on their machines? I'm running on a Macbook Pro (Intel Core2 processor, probably Merom) with a 32-bit build from Apple's gcc-4.0.1. (Apple's gcc consistently produces a faster python than gcc-4.3.)
2) Assuming this speeds things up for most people, should I check it in anywhere besides the trunk? I assume it's out for 3.0; is it in for 2.6.1 or 3.0.1?
Pybench output:
------------------------------------------------------------------------------- PYBENCH 2.0 ------------------------------------------------------------------------------- * using CPython 2.7a0 (trunk:67458M, Nov 30 2008, 17:14:10) [GCC 4.0.1 (Apple Inc. build 5488)] * disabled garbage collection * system check interval set to maximum: 2147483647 * using timer: time.time
------------------------------------------------------------------------------- Benchmark: pybench.out -------------------------------------------------------------------------------
Rounds: 10 Warp: 10 Timer: time.time
Machine Details: Platform ID: Darwin-9.5.0-i386-32bit Processor: i386
Python: Implementation: CPython Executable: /Users/jyasskin/src/python/trunk-fast-tracing/build/python.exe Version: 2.7.0 Compiler: GCC 4.0.1 (Apple Inc. build 5488) Bits: 32bit Build: Nov 30 2008 17:14:10 (#trunk:67458M) Unicode: UCS2
------------------------------------------------------------------------------- Comparing with: ../build_orig/pybench.out -------------------------------------------------------------------------------
Rounds: 10 Warp: 10 Timer: time.time
Machine Details: Platform ID: Darwin-9.5.0-i386-32bit Processor: i386
Python: Implementation: CPython Executable: /Users/jyasskin/src/python/trunk-fast-tracing/build_orig/python.exe Version: 2.7.0 Compiler: GCC 4.0.1 (Apple Inc. build 5488) Bits: 32bit Build: Nov 30 2008 13:51:09 (#trunk:67458) Unicode: UCS2
Test minimum run-time average run-time this other diff this other diff ------------------------------------------------------------------------------- BuiltinFunctionCalls: 127ms 130ms -2.4% 129ms 132ms -2.1% BuiltinMethodLookup: 90ms 93ms -3.2% 91ms 94ms -3.1% CompareFloats: 88ms 91ms -3.3% 89ms 93ms -4.3% CompareFloatsIntegers: 97ms 99ms -2.1% 97ms 100ms -2.4% CompareIntegers: 79ms 82ms -4.2% 79ms 85ms -6.1% CompareInternedStrings: 90ms 92ms -2.4% 94ms 94ms -0.9% CompareLongs: 86ms 83ms +3.6% 87ms 84ms +3.5% CompareStrings: 80ms 82ms -3.1% 81ms 83ms -2.3% CompareUnicode: 103ms 105ms -2.3% 106ms 108ms -1.5% ComplexPythonFunctionCalls: 139ms 137ms +1.3% 140ms 139ms +0.1% ConcatStrings: 142ms 151ms -6.0% 156ms 154ms +1.1% ConcatUnicode: 87ms 92ms -5.4% 89ms 94ms -5.7% CreateInstances: 142ms 144ms -1.4% 144ms 145ms -1.1% CreateNewInstances: 107ms 109ms -2.3% 108ms 111ms -2.1% CreateStringsWithConcat: 114ms 137ms -17.1% 117ms 139ms -16.0% CreateUnicodeWithConcat: 92ms 101ms -9.2% 95ms 102ms -7.2% DictCreation: 77ms 81ms -4.4% 80ms 85ms -5.9% DictWithFloatKeys: 91ms 107ms -14.5% 93ms 109ms -14.6% DictWithIntegerKeys: 95ms 94ms +1.4% 108ms 96ms +12.3% DictWithStringKeys: 83ms 88ms -5.8% 84ms 88ms -4.7% ForLoops: 72ms 72ms -0.1% 79ms 74ms +5.8% IfThenElse: 83ms 80ms +3.9% 85ms 80ms +5.3% ListSlicing: 117ms 118ms -0.7% 118ms 121ms -1.8% NestedForLoops: 116ms 119ms -2.4% 121ms 121ms +0.0% NormalClassAttribute: 106ms 115ms -7.7% 108ms 117ms -7.7% NormalInstanceAttribute: 96ms 98ms -2.3% 97ms 100ms -3.1% PythonFunctionCalls: 92ms 95ms -3.7% 94ms 99ms -5.2% PythonMethodCalls: 147ms 147ms +0.1% 152ms 149ms +2.1% Recursion: 135ms 136ms -0.3% 140ms 144ms -2.9% SecondImport: 101ms 99ms +2.1% 103ms 101ms +2.2% SecondPackageImport: 107ms 103ms +3.5% 108ms 104ms +3.3% SecondSubmoduleImport: 134ms 134ms +0.3% 136ms 136ms -0.0% SimpleComplexArithmetic: 105ms 111ms -5.0% 110ms 112ms -1.4% SimpleDictManipulation: 95ms 106ms -10.6% 96ms 109ms -12.0% SimpleFloatArithmetic: 90ms 99ms -9.3% 93ms 102ms -8.2% SimpleIntFloatArithmetic: 78ms 76ms +2.3% 79ms 77ms +2.0% SimpleIntegerArithmetic: 78ms 77ms +1.8% 79ms 77ms +2.0% SimpleListManipulation: 80ms 78ms +2.4% 80ms 79ms +1.9% SimpleLongArithmetic: 110ms 113ms -2.0% 111ms 113ms -2.1% SmallLists: 128ms 117ms +9.5% 130ms 124ms +4.9% SmallTuples: 115ms 114ms +1.7% 117ms 114ms +2.2% SpecialClassAttribute: 101ms 112ms -10.3% 104ms 114ms -8.9% SpecialInstanceAttribute: 173ms 177ms -1.9% 176ms 179ms -1.6% StringMappings: 165ms 167ms -1.2% 168ms 169ms -0.5% StringPredicates: 126ms 134ms -5.7% 127ms 134ms -5.6% StringSlicing: 125ms 123ms +1.9% 131ms 130ms +0.7% TryExcept: 79ms 80ms -0.6% 80ms 80ms -0.8% TryFinally: 110ms 107ms +3.0% 111ms 112ms -1.1% TryRaiseExcept: 99ms 101ms -1.6% 100ms 102ms -1.7% TupleSlicing: 127ms 127ms +0.6% 137ms 137ms +0.0% UnicodeMappings: 144ms 144ms -0.3% 145ms 145ms -0.4% UnicodePredicates: 116ms 114ms +1.3% 117ms 115ms +1.1% UnicodeProperties: 106ms 102ms +3.6% 107ms 104ms +3.1% UnicodeSlicing: 95ms 111ms -14.0% 99ms 112ms -11.8% WithFinally: 157ms 152ms +3.3% 159ms 154ms +3.3% WithRaiseExcept: 123ms 125ms -1.1% 125ms 126ms -1.2% ------------------------------------------------------------------------------- Totals: 6043ms 6182ms -2.2% 6185ms 6301ms -1.9%
(this=pybench.out, other=../build_orig/pybench.out)
2to3 times:
Before: $ time ./python.exe ~/src/2to3/2to3 -f all ~/src/2to3/ >/dev/null real 0m56.685s user 0m55.620s sys 0m0.380s
After: $ time ./python.exe ~/src/2to3/2to3 -f all ~/src/2to3/ >/dev/null real 0m55.067s user 0m53.843s sys 0m0.376s
== 3% faster
Gory details:
The meat of the patch is: @@ -884,11 +891,12 @@ fast_next_opcode: f->f_lasti = INSTR_OFFSET();
/* line-by-line tracing support */
- if (tstate->c_tracefunc != NULL && !tstate->tracing) { + if (_Py_TracingPossible && + tstate->c_tracefunc != NULL && !tstate->tracing) {
This converts the generated assembly (produced with `gcc -S -dA ...`, then manually annotated a bit) from:
# basic block 17 # ../Python/ceval.c:885 LM541: movl 8(%ebp), %ecx LVL319: subl -316(%ebp), %edx movl %edx, 60(%ecx) # ../Python/ceval.c:889 LM542: # %esi = tstate movl -336(%ebp), %esi LVL320: # %eax = tstate->c_tracefunc movl 28(%esi), %eax LVL321: # if tstate->c_tracefunc == 0 testl %eax, %eax # goto past-if () je L567 # more if conditions here
to:
# basic block 17 # ../Python/ceval.c:889 LM542: movl 8(%ebp), %ecx LVL319: subl -316(%ebp), %edx movl %edx, 60(%ecx) # ../Python/ceval.c:893 LM543: # %eax = _Py_TracingPossible movl __Py_TracingPossible-"L00000000033$pb"(%ebx), %eax LVL320: # if _Py_TracingPossible != 0 testl %eax, %eax # goto rest-of-if (nearby) jne L2321 # opcode = NEXTOP(); continues here
The branch should be predicted accurately either way, so there are 2 things that may be contributing to the performance change.
First, adding the global caching variable halves the amount of memory that has to be read to check the prediction. The memory that is read is still read one instruction before it's used, but adding a local variable to read the memory earlier doesn't affect the performance.
Without the global variable, the compiler puts the tracing code immediately after the if; with the global, it moves it away and puts the non-tracing code immediately after the first test in the if. This may affect branch prediction and may affect the icache. I tried using gcc's __builtin_expect() to ensure that the tracing code is always out-of-line. This moved it much farther away and cost about 1% in performance (i.e. 1% instead of 2% faster than "before"). I don't know why the __builtin_expect() version would be slower. If anyone feels inspired to test this out on another processor or compiler version, let me know how it goes.
Jeffrey
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-- Namasté, Jeffrey Yasskin http://jeffrey.yasskin.info/