Interpreting the Dhrystone Benchmark results on Modern PC - c

Question

First I'll give a run down on what I did.
I downloaded dhry.h dhry_1.c and dhry_2.c from here:
http://giga.cps.unizar.es/~spd/src/other/dhry/
Then I made some corrections (so that I would compile) according to this:
https://github.com/maximeh/buildroot/blob/master/package/dhrystone/dhrystone-2-HZ.patch
And this
Errors while compiling dhrystone in unix
I've compiled the files with the following command line:
gcc dhry_1.c dhry_2.c -O2 -o run
I finally entered the number of runs to be 1000000000
And waited. I compiled with four different optimization levels and I got these values of DMIPS (According to http://en.wikipedia.org/wiki/Dhrystone this is the Dhrystones per Second divided by 1757):
O0: 8112 O1: 16823.9 O2: 22977.5 O3: 23164.5 (these represent the compiler flags like -O2 is optimization level two and O0 is none).
This would give the following DMIPS/MHz (base frequency for my processor is 3.4 GHz):
2.3859 4.9482 6.7581 6.8131
However, I get the feelign tha 6.7 is way to low. According to what I've read an A15 has between 3.5 to 4 DMIPS/MHz and a third generation I7 only has double that? Shouldn't it be a lot higher?
Can anyone tell me from my procedure if they can see that I might have done something wrong? Or maybe I'm interpretting the results incorrectly?

Answer 1

Except with a broad brush treatment, you cannot compare benchmark results produced by different compilers. As the design authority of the first standard benchmark (Whetstone), I can advise that it even less safe to include comparisons with results from a computer manufacturer’s in-house compiler. In minicomputer days, manufacturers found that sections of the Whetstone benchmark could be optimised out, to double the score. I arranged for changes and more detailed results to avoid and later highlight over optimisation.
Below are example results on PCs from my original (1990’s) Dhrystone Benchmarks. For details, more results and (free) execution and source files see:
http://www.roylongbottom.org.uk/dhrystone%20results.htm
Also included, and compiled from the same source code, are results from a later MS compiler and some via Linux and on Android, via ARM CPUs, plus one for an Intel Atom, via Houdini compatibility layer. I prefer the term VAX MIPS instead to DMIPS, as the 1757 divisor is the result on DEC VAX 11/780. Anyway, MIPS/MHz calculations are also shown. Note differences due to compilers and the particularly low ratios on Android ARM CPUs.
Dhry1 Dhry1 Dhry2 Dhry2 Dhry2
Opt NoOpt Opt NoOpt Opt
VAX VAX VAX VAX MIPS/
CPU MHz MIPS MIPS MIPS MIPS MHz
AMD 80386 40 17.5 4.32 13.7 4.53 0.3
80486 DX2 66 45.1 12 35.3 12.4 0.5
Pentium 100 169 31.8 122 32.2 1.2
Pentium Pro 200 373 92.4 312 91.9 1.6
Pentium II 300 544 132 477 136 1.6
Pentium III 450 846 197 722 203 1.6
Pentium 4 1900 2593 261 2003 269 1.1
Atom 1666 2600 772 1948 780 1.2
Athlon 64 2211 5798 1348 4462 1312 2.0
Core 2 Duo 1 CP 2400 7145 1198 6446 1251 2.7
Phenom II 1 CP 3000 9462 2250 7615 2253 2.5
Core i7 4820K 3900 14776 2006 11978 2014 3.1
Later Intel Compiler
Pentium 4 1900 2613 1795 0.9
Athlon 64 2211 6104 3720 1.7
Core 2 Duo 2400 8094 5476 2.3
Phenom II 3000 9768 6006 2.0
Core i7 4820K 3900 15587 10347 2.7
Linux Ubuntu GCC Compiler
Atom 1666 5485 1198 2055 1194 1.2
Athlon 64 2211 9034 2286 4580 2347 2.1
Core 2 Duo 2400 13599 3428 5852 3348 2.4
Phenom II 3000 13406 3368 6676 3470 2.2
Core i7 4820K 3900 29277 7108 16356 7478 4.2
ARM Android NDK
926EJ 800 356 196 0.4
v7-A9 1500 1650 786 1.1
v7-A15 1700 3189 1504 1.9
Atom Houdini 1866 1840 1310 1.0