C++ uses 34% more energy than C?
I thought C code was generally also valid C++ code and so you really should be able to get the same performance and energy consumption. Very odd.
I thought C code was generally also valid C++ code and so you really should be able to get the same performance and energy consumption. Very odd.
> it won’t be idiomatic
I just looked at the first example:
C: https://benchmarksgame-team.pages.debian.net/benchmarksgame/...
C++: https://benchmarksgame-team.pages.debian.net/benchmarksgame/...
The C++ doesn’t use shared_ptr or STL or anything, and isn’t that far from the C code, but it isn’t that close either. I wonder if it’s OMP configuration that’s causing it to be slower, or maybe just instruction cache or something since the C++ is larger.
The results say this one has C++ going 50% slower. I’m a little skeptical it’s the compiler’s or the language’s fault. I’d speculate it might have more to do with how the program is written.
The "Energy Efficiency across Programming Languages, SLE’17"authors provided this repo —
https://github.com/greensoftwarelab/Energy-Languages/blob/ma...
https://github.com/greensoftwarelab/Energy-Languages/tree/ma...
For a single outlier (regex-redux) there's a 12x difference between the measured times of the selected C and C++ programs.
Even so, that mostly messes up the results because the arithmetic mean is used rather than the median.
https://benchmarksgame-team.pages.debian.net/benchmarksgame/...
Your bottom link shows the same data I see using the link in the article: the C++ is ~50% slower on spectral-norm.
I expect that the 12x outlier is because someone did something very non-optimal in C++.
No, the link grabbing seo provides the correct source for Table 4 — "Source: Energy Efficiency across Programming Languages, SLE’17" — and google finds the article:
https://greenlab.di.uminho.pt/wp-content/uploads/2017/09/pap...
> looks the same
Please look again.
> the 12x outlier
#include <pcre.h>
vs
#include <boost/regex.hpp>I assume you’re referring to regex-redux, but I was confused for a minute there because you linked directly to the C++ code for spectral-norm, not regex-redux, and spectral-norm doesn’t include a regex lib. I had to go looking around for the includes you’re talking about, and the Benchmarks-Game version has multiple C++ entries. There are C++ entries that use pcre, re2, and boost/regex. The C entries all use pcre except the winner, who uses pcre2.
> For a single outlier (regex-redux) there's a 12x difference between the measured times of the selected C and C++ programs.
BTW, I dont know exactly what they’re referring to there. The time ratio of the Benchmarks Game fastest C version to the slowest C++ version is over 16x. The ratios in the SLE paper of energy and run time are a bit lower than 12 but they also have only one sample, and it uses boost, so I don’t see why regex-redux with boost is useful in any perf or energy comparison other than to serve as a mild warning about using boost.
There happens to be a ratio of almost exactly 12x between the slowest C++ version (g++#3 boost) and the fastest C++ version (g++#6 - pcre2). That’s C++ vs C++. Maybe that’s what they were talking about, or maybe the perf numbers have changed out from under the commentary.
The ratio of times of the fastest C to the fastest C++ time with regex-redux is 1.4x and they both use pcre2. That seems like a more reasonable place to start.
We're comparing averages, why would we bother so much about the cause of an outlier.
> you linked directly to the C++ code for spectral-norm
You had linked to the wrong C and C++ code for spectral-norm, I linked to the code that was actually used.
> The time ratio of the Benchmarks Game fastest C version to the slowest C++ version is over 16x.
Again, you seem to be looking at the wrong repo.
The authors of "Energy Efficiency across Programming Languages, SLE’17" provided this repo —
Why? The benchmarks game doesn't show energy use of programs.
> use of boost is the entire reason
As you know, the fastest C++ program shown on the benchmarks game website uses pcre2.h.