On 3/9/2011 5:23 PM, Chad Nelson wrote:
Below are the comparative timings with and without Copy-on-Write, and with and without Boost.Move.
Times are measured in seconds, using two sets of ten integers (512, 2048, and 8192 bit). The tests consisted of adding each of those pairs of numbers together 10,000 times, multiplying them 10,000 times, and doing a "mulmod" operation on them (with a third randomly-generated modulus argument of the same size) 1,000 times. Each test was run three times, under as close to identical situations as I could manage, with the raw results in the first three columns; the fourth column is the average of the three.
The compiler used was GCC 4.5.1, under Ubuntu Linux 10.10. The build was non-debug and used -O2 optimization. Otherwise, the settings were left at their defaults.
The "review code" lines are for the unmodified review version of the code. All others are for the pass-by-reference version, with several other modifications that should have no measurable effect on the speed.
The tests show pretty conclusively that Copy-on-Write, alone or in conjunction with Boost.Move, provides a noticeable speed improvement on all three sizes. They also prove that Boost.Move can work well in conjunction with it. I'll leave any further analysis to people who are probably more qualified than I.
Note that the Boost.Move numbers could be a little better. The integer_t classes are move-enabled, but the internal data class is not as yet. The data class only sometimes uses return values, so the difference isn't likely to be great.
I will make the updated code available on request for anyone who wants to examine the changes.
512bit CoW, no Move: 0.48, 0.47, 0.47: 0.48 No CoW, no Move: 0.61, 0.61, 0.62: 0.61 (worst) No CoW, Move: 0.57, 0.57, 0.55: 0.56 CoW, Move: 0.44, 0.44, 0.44: 0.44 (best)
Review code, CoW, no Move: 0.50, 0.47, 0.47: 0.48
2Kbit CoW, no Move: 4.69, 4.79, 4.89: 4.79 (best) No CoW, no Move: 5.01, 5.19, 5.06: 5.09 (worst) No CoW, Move: 5.18, 5.00, 5.01: 5.06 CoW, Move: 4.80, 4.79, 4.86: 4.82
Review code, CoW, no Move: 4.88, 4.85, 4.94: 4.89
8Kbit CoW, no Move: 68.0, 68.8, 68.9: 68.6 No CoW, no Move: 70.4, 70.4, 70.2: 70.3 (worst) No CoW, Move: 70.9, 69.8, 69.6: 70.1 CoW, Move: 68.4, 68.2, 67.8: 68.1 (best)
Review code, CoW, no Move: 68.8, 68.4, 68.8: 68.7
To echo Steven's request, please make your test code available. The 2Kbit section has me wondering about the accuracy of these timings, as "CoW, no Move" outperformed "CoW, Move", which should definitely not be the case. I can't think of any circumstance where move emulation gives you a penalty... I think an equally important measure would be the # of allocation requests. Do you track those? - Jeff