[Beowulf] Q: AMD Opteron (Barcelona) 2356 vs Intel Xeon 5460
forum.san at gmail.com
Wed Sep 17 22:35:55 PDT 2008
The scientific application used is Dl-Poly - 2.17.
Tested with Pathscale and Intel compilers on AMD Opteron Quad core. The time
figures mentioned were taken from DL-Poly output file. Also I had used time
command. Here are the results:
AMD-2.3GHz (32 GB RAM)
INTEL-2.33GHz (32 GB RAM)
GNU gfortran Pathscale Intel 10
ifort Intel 10 fiort
OUTPUT file 147.719 sec 158.158 sec 135.729 sec
Time command 2m27.791s
OUTPUT file 39.798 sec 44.717 sec 36.962 sec
Time Command 0m41.527s
OUTPUT 26.880 sec 33.746 sec 27.979 sec
The optimization flags used:
Intel ifort 10: -O3 -axW -funroll-loops (don't remember exact
flag. Similar to loop unroll)
Pathscale: -O3 -OPT:Ofast -ffast-math -fno-math-errno
GNU gfortran -O3 -ffast-math -funroll-all-loops -ftree-vectorize
I'll try to use the further: http://directory.fsf.org/project/time/
On Thu, Sep 18, 2008 at 6:07 AM, Vincent Diepeveen <diep at xs4all.nl> wrote:
> How does all this change when you use a PGO optimized executable on both
> On Sep 18, 2008, at 2:34 AM, Eric Thibodeau wrote:
> Vincent Diepeveen wrote:
>>> I guess he's referring to sometimes it's using single precision floating
>>> to get something done instead of double precision, and it tends to keep
>>> sometimes stuff in registers.
>>> That isn't a problem necessarily, but if i remember well floating point
>>> could get wiped out when switching to SSE2.
>>> Sometimes you lose your FPU registerset in that case.
>>> Main problem is that there is so many dangerous optimizations possible,
>>> to speedup testsets, because in itself floating point is real slow to do
>>> at hardware,
>>> from hardware viewpoint seen.
>>> Yet in general last generations of intel compilers that has improved
>>> really a lot.
>> Well, running the same code here is the result discrepancy I got:
>> my code has to do: 7,975,847,125,000 (~8Tflops) ...takes 15minutes on
>> 8*2core Opeteron with 32 Gigs-o-RAM (thank you OpenMP ;)
>> The running times (ran it a _few_ times...but not the statistical minimum
>> of 30):
>> ICC -> runtime == 689.249 ; summed error == 1651.78
>> GCC -> runtime == 1134.404 ; summed error == 0.883501
>> Compiler Flags:
>> icc -xW -openmp -O3 vqOpenMP.c -o vqOpenMP
>> gcc -lm -fopenmp -O3 -march=native vqOpenMP.c -o vqOpenMP_GCC
>> No trickery, no smoky mirrors ;) Just a _huge_ kick ASS k-Means
>> parallelized with OpenMP (thank gawd, otherwise it takes hours to run) and a
>> rather big database of 1.4 Gigs
>> ... So this is what I meant by floating point errors. Yes, the runtime was
>> almost halved by ICC (and this is on an *opteron* based system, Tyan VX50).
>> The running time wasn't what I was actually looking for rather than
>> precision skew and that's where I fell off my chair.
>> For the ones itching for a little more specs:
>> eric at einstein ~ $ icc -V
>> Intel(R) C Compiler for applications running on Intel(R) 64, Version 10.1
>> Build 20080602
>> Copyright (C) 1985-2008 Intel Corporation. All rights reserved.
>> FOR NON-COMMERCIAL USE ONLY
>> eric at einstein ~ $ gcc -v
>> Using built-in specs.
>> Target: x86_64-pc-linux-gnu
>> Configured with:
>> --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.3.1
>> --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec
>> --enable-nls --without-included-gettext --with-system-zlib
>> --disable-checking --disable-werror --enable-secureplt --enable-multilib
>> --enable-libmudflap --disable-libssp --enable-cld --disable-libgcj
>> --enable-languages=c,c++,treelang,fortran --enable-shared
>> --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
>> --with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.3.1-r1
>> Thread model: posix
>> gcc version 4.3.1 (Gentoo 4.3.1-r1 p1.1)
>>> On Sep 17, 2008, at 10:25 PM, Greg Lindahl wrote:
>>> On Wed, Sep 17, 2008 at 03:43:36PM -0400, Eric Thibodeau wrote:
>>>> Also, note that I've had issues with icc
>>>>> generating really fast but inaccurate code (fp model is not IEEE *by
>>>>> default*, I am sure _everyone_ knows this and I am stating the obvious
>>>> All modern, high-performance compilers default that way. It's certainly
>>>> the case that sometimes it goes more horribly wrong than necessary, but
>>>> I wouldn't ding icc for this default. Compare results with IEEE mode.
>>>> -- greg
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