| msg63426 - (view) |
Author: Jeffrey Yasskin (jyasskin) *  |
Date: 2008-03-09 17:38 |
| I'm using Apple's gcc-4.0.1 on a 2.33GHz Intel Core 2 Duo to test this. Measurements from other compilers or other chips would be cool. Specifically, this patch: 1) Moves the declarations of most of the local variables inside the for(;;) loop. That shortens their lifetimes so that the compiler can skip spilling them to memory in some cases. Pushing them further down into the individual case statements didn't change the generated assembly in most cases, although there are probably a few opcodes where it would. 2) Eliminates the initialization of w, and fixes the "possibly used uninitialized" warning by changing how the PRINT opcodes initialize it from stream. That lets my compiler avoid using its stack entry most of the time. 3) In two hot opcodes, LOAD_FAST and LOAD_CONST, changes the 'x' to a 'w'. 'x' is always written to memory because it's used for error detection, while 'w' can stay on the stack. 4) Changes --_Py_Ticker in the periodic things check to _Py_Ticker--. Because _Py_Ticker is volatile, predecrement (at least on my compiler) needs 3 memory accesses, while postdecrement gets away with 2. Together, these changes are worth about 3% on pybench on my machine. |
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| msg63427 - (view) |
Author: Neal Norwitz (nnorwitz) * |
Date: 2008-03-09 18:45 |
| I bet with just a little more work, you could get rid of t and stream. t is only used for a single set of opcodes (STORE_SLICE+n). stream is only used for the PRINT opcodes. The code in print could be moved to a function which might allow the compiler to do a better job. I'll benchmark this later on amd64 and amd x86 linux boxes. Maybe mac ppc g4 if I'm adventurous. :-) |
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| msg63428 - (view) |
Author: Neal Norwitz (nnorwitz) * |
Date: 2008-03-09 18:47 |
| Can't next_instr and stack_pointer move inside the for loop too? |
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| msg63431 - (view) |
Author: Skip Montanaro (skip.montanaro) *  |
Date: 2008-03-10 01:23 |
| I've yet to run pybench, but I came get these warnings from the compiler after applying the patch: ../Python/ceval.c: In function 'PyEval_EvalFrameEx': ../Python/ceval.c:772: warning: 'x' may be used uninitialized in this function ../Python/ceval.c:770: warning: 'err' may be used uninitialized in this function Platform is Mac OS X 10.5.2 MacBook Pro, gcc version 4.0.1 (Apple Inc. build 5465) |
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| msg63432 - (view) |
Author: Skip Montanaro (skip.montanaro) * |
Date: 2008-03-10 01:43 |
| Pybench doesn't show much difference for me, about 0.1% better on minimum times. A few tests are quite a bit worse (> 10%) with the patch (Recursion, SimpleFloatArithmetic, StringPredicates, TryFinally). A few are quite a bit better (CompareFloatsIntegers, CompareIntegers, DictWithFloatKeys). |
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| msg63434 - (view) |
Author: Jeffrey Yasskin (jyasskin) * |
Date: 2008-03-10 05:51 |
| Neal, t and stream aren't likely to have much effect since they're used so little. next_instr and stack_pointer are used to communicate between loops, so they can't move inside. I eagerly await your benchmark runs. :) Skip, I managed to reproduce the warnings with gcc-4.2.1, and while they're wrong, I see why they're happening. The if (throwflag) block skips to on_error, which misses the initializations of x and err. The right way to fix it is either to eliminate the error-reporting behavior of x and err or to extract on_error into a function, but for this patch I would probably just keep x and err out of the loop. Your numbers made me look closer at my results for individual tests, and I'm now confused about how reliable pybench is. My gcc-4.0 was build #5367 on OS X 10.4.11, and MacPorts' gcc-4.2.1 (with a necessary configure.in tweak) still shows a 1-2% gain overall. But contrary to your numbers, it gives me a 10% speedup in Recursion and a 1% slowdown in CompareFloatsIntegers. My big losers are SimpleListManipulation with an 18% loss on 4.2 and CompareInternedStrings with a 20% loss on 4.0, but those are both small winners (~5%) on the opposite compiler! I wouldn't be surprised if the overall numbers were different between even slightly different machines and compilers, but I'm really surprised to see the same tests affected in opposite directions. Is that common with pybench and compiler changes? |
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| msg63439 - (view) |
Author: Skip Montanaro (skip.montanaro) * |
Date: 2008-03-10 12:44 |
| Jeffrey> ... but I'm really surprised to see the same tests affected in Jeffrey> opposite directions. Is that common with pybench and compiler Jeffrey> changes? I've no idea. Marc-André Lemburg would be the person with the most insight into pybench behavior I think. Skip |
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| msg63860 - (view) |
Author: Jeffrey Yasskin (jyasskin) * |
Date: 2008-03-18 03:03 |
| Another data point: I just installed gcc-4.3.0, and the second patch gives it a 6% speedup. On the downside, 4.3 is still about 9% slower than 4.0. :-( Neal, do you have your measurements? |
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| msg63903 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2008-03-18 07:10 |
| We really could use an automated pybench runner on a dedicated machine driven by a buildbot feeding its results into a database so that we had a record of exactly when/what caused performance changes over time. This sounds remarkably like some of the work I was doing at my last job... ;) I'll run some benchmarks using this patch of my own and on the grander scale ponder what I need to make a dedicated automated Python benchmark server happen. |
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| msg188401 - (view) |
Author: Antoine Pitrou (pitrou) * |
Date: 2013-05-04 19:58 |
| This avenue doesn't look promising at all. Closing. |
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