[gentoo-user] Changing compilers

[gentoo-user] Changing compilers

[Andrew Lowe]

Hi all,
     Has anyone played around with the various "better known"  
compilers on Gentoo? By "better known", I'm referring to gcc, Intel,  
llvm, pathscale. My situation is that I've just started my PhD which  
requires me to do Finite Element Analysis, FEA, and Computational  
Fluid Dynamics, CFD, and I want to find the "best" compiler for the  
job. Before anyone says "Why bother, XXX compiler is only 1 - 2%  
faster than gcc", in the context of the work I'm doing this 1 - 2% IS  
important.

What I'm looking for is any feedback people may have on ability to  
compile the Gentoo environment, the ability to change compilers  
easily, gcc-config or flags in make.conf, as to whether the  
compiler/linker can use the libraries as compiled by gcc on a  
"standard" gentoo install and so on. Obviously there is much web  
trawling to be done to find what other people are saying as well.

Any thoughts, greatly appreciated,
        Andrew Lowe

Re: [gentoo-user] Changing compilers

[Matthew Finkel]

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On Mon, Mar 19, 2012 at 1:26 AM, Andrew Lowe <agl@wht.com.au> wrote:

> Hi all,
>    Has anyone played around with the various "better known" compilers on
> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
> situation is that I've just started my PhD which requires me to do Finite
> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
> find the "best" compiler for the job. Before anyone says "Why bother, XXX
> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
> doing this 1 - 2% IS important.
>
> What I'm looking for is any feedback people may have on ability to compile
> the Gentoo environment, the ability to change compilers easily, gcc-config
> or flags in make.conf, as to whether the compiler/linker can use the
> libraries as compiled by gcc on a "standard" gentoo install and so on.
> Obviously there is much web trawling to be done to find what other people
> are saying as well.
>
> Any thoughts, greatly appreciated,
>       Andrew Lowe
>
>
With regard to speed, are you looking for a faster compile time or higher
optimization of the compiled code such that the run time is faster?


-- 
Matthew Finkel

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Re: [gentoo-user] Changing compilers

[Andrew Lowe]

Quoting Matthew Finkel <matthew.finkel@gmail.com>:

> On Mon, Mar 19, 2012 at 1:26 AM, Andrew Lowe <agl@wht.com.au> wrote:
>
>> Hi all,

[snip]

>>
>> Any thoughts, greatly appreciated,
>>       Andrew Lowe
>>
>>
> With regard to speed, are you looking for a faster compile time or higher
> optimization of the compiled code such that the run time is faster?
>
>
> --
> Matthew Finkel

I'm looking for the faster code, the run time to be faster - I compile  
the FEA & CFD code once but will be running many jobs.

Andrew

[gentoo-user] Re: Changing compilers

[Nikos Chantziaras]

On 19/03/12 07:26, Andrew Lowe wrote:
> Hi all,
> Has anyone played around with the various "better known" compilers on
> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale.
> My situation is that I've just started my PhD which requires me to do
> Finite Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and
> I want to find the "best" compiler for the job. Before anyone says "Why
> bother, XXX compiler is only 1 - 2% faster than gcc", in the context of
> the work I'm doing this 1 - 2% IS important.
>
> What I'm looking for is any feedback people may have on ability to
> compile the Gentoo environment, the ability to change compilers easily,
> gcc-config or flags in make.conf, as to whether the compiler/linker can
> use the libraries as compiled by gcc on a "standard" gentoo install and
> so on. Obviously there is much web trawling to be done to find what
> other people are saying as well.

You don't need to "change" compilers.  You can use whatever one you like 
to build your program.  The compiler portage uses to build its packages 
does not affect your own usage of the others.

As for the fastest one, I can only speak for Intel CPUs where Intel C++ 
gives me the fastest binaries.

Re: [gentoo-user] Changing compilers

[Michael Mol]

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FEA jobs can be parallelized, right? Take a hard look at CUDA and OpenCL.

ZZ
On Mar 19, 2012 1:29 AM, "Andrew Lowe" <agl@wht.com.au> wrote:

> Hi all,
>    Has anyone played around with the various "better known" compilers on
> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
> situation is that I've just started my PhD which requires me to do Finite
> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
> find the "best" compiler for the job. Before anyone says "Why bother, XXX
> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
> doing this 1 - 2% IS important.
>
> What I'm looking for is any feedback people may have on ability to compile
> the Gentoo environment, the ability to change compilers easily, gcc-config
> or flags in make.conf, as to whether the compiler/linker can use the
> libraries as compiled by gcc on a "standard" gentoo install and so on.
> Obviously there is much web trawling to be done to find what other people
> are saying as well.
>
> Any thoughts, greatly appreciated,
>       Andrew Lowe
>
>
>

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Re: [gentoo-user] Changing compilers

[Mark Knecht]

On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe <agl@wht.com.au> wrote:
> Hi all,
>    Has anyone played around with the various "better known" compilers on
> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
> situation is that I've just started my PhD which requires me to do Finite
> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
> find the "best" compiler for the job. Before anyone says "Why bother, XXX
> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
> doing this 1 - 2% IS important.
>
> What I'm looking for is any feedback people may have on ability to compile
> the Gentoo environment, the ability to change compilers easily, gcc-config
> or flags in make.conf, as to whether the compiler/linker can use the
> libraries as compiled by gcc on a "standard" gentoo install and so on.
> Obviously there is much web trawling to be done to find what other people
> are saying as well.
>
> Any thoughts, greatly appreciated,
>       Andrew Lowe
>
>

Think CUDA

Mark

Re: [gentoo-user] Changing compilers

[Mark Knecht]

On Mon, Mar 19, 2012 at 5:32 AM, Mark Knecht <markknecht@gmail.com> wrote:
> On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe <agl@wht.com.au> wrote:
>> Hi all,
>>    Has anyone played around with the various "better known" compilers on
>> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
>> situation is that I've just started my PhD which requires me to do Finite
>> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
>> find the "best" compiler for the job. Before anyone says "Why bother, XXX
>> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
>> doing this 1 - 2% IS important.
>>
>> What I'm looking for is any feedback people may have on ability to compile
>> the Gentoo environment, the ability to change compilers easily, gcc-config
>> or flags in make.conf, as to whether the compiler/linker can use the
>> libraries as compiled by gcc on a "standard" gentoo install and so on.
>> Obviously there is much web trawling to be done to find what other people
>> are saying as well.
>>
>> Any thoughts, greatly appreciated,
>>       Andrew Lowe
>>
>>
>
> Think CUDA
>
> Mark

Sorry. Meant to include this reference: <$15 on Kindle. Reads great on
Kindle for PC.

http://www.amazon.com/CUDA-Example-Introduction-General-Purpose-ebook/dp/B003VYBOSE/ref=sr_1_4?ie=UTF8&qid=1332160431&sr=8-4

Re: [gentoo-user] Changing compilers

[Michael Mol]

On Mon, Mar 19, 2012 at 8:32 AM, Mark Knecht <markknecht@gmail.com> wrote:
> On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe <agl@wht.com.au> wrote:
>> Hi all,
>>    Has anyone played around with the various "better known" compilers on
>> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
>> situation is that I've just started my PhD which requires me to do Finite
>> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
>> find the "best" compiler for the job. Before anyone says "Why bother, XXX
>> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
>> doing this 1 - 2% IS important.
>>
>> What I'm looking for is any feedback people may have on ability to compile
>> the Gentoo environment, the ability to change compilers easily, gcc-config
>> or flags in make.conf, as to whether the compiler/linker can use the
>> libraries as compiled by gcc on a "standard" gentoo install and so on.
>> Obviously there is much web trawling to be done to find what other people
>> are saying as well.
>>
>> Any thoughts, greatly appreciated,
>>       Andrew Lowe
>>
>>
>
> Think CUDA

Yes. And as a convenient side-effect, it offers a great excuse to
upgrade your video card with some regularity. The performance of
mid-grade and high-grade video cards continues to improve rapidly.

-- 
:wq

Re: [gentoo-user] Changing compilers

[Andrew Lowe]

On 03/19/12 20:34, Mark Knecht wrote:
> On Mon, Mar 19, 2012 at 5:32 AM, Mark Knecht <markknecht@gmail.com> wrote:
>> On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe <agl@wht.com.au> wrote:
>>> Hi all,
>>>    Has anyone played around with the various "better known" compilers on
>>> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
>>> situation is that I've just started my PhD which requires me to do Finite
>>> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
>>> find the "best" compiler for the job. Before anyone says "Why bother, XXX
>>> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
>>> doing this 1 - 2% IS important.
>>>
>>> What I'm looking for is any feedback people may have on ability to compile
>>> the Gentoo environment, the ability to change compilers easily, gcc-config
>>> or flags in make.conf, as to whether the compiler/linker can use the
>>> libraries as compiled by gcc on a "standard" gentoo install and so on.
>>> Obviously there is much web trawling to be done to find what other people
>>> are saying as well.
>>>
>>> Any thoughts, greatly appreciated,
>>>       Andrew Lowe
>>>
>>>
>>
>> Think CUDA
>>
>> Mark
> 
> Sorry. Meant to include this reference: <$15 on Kindle. Reads great on
> Kindle for PC.
> 
> http://www.amazon.com/CUDA-Example-Introduction-General-Purpose-ebook/dp/B003VYBOSE/ref=sr_1_4?ie=UTF8&qid=1332160431&sr=8-4
> 
> 

	I'm sorry but I'm doing a PhD, not creating a career in Academia. The
concept of writing an FEA or CFD from scratch, with CUDA is laughable, I
just don't have the time to learn CUDA, research the field, small
displacement, large displacement, dynamics, material nonlinearities,
write the code, and then most importantly benchmark it to make sure it's
actually correct. This is all bearing in mind that I have 20+ years
experience as a C/C++ technical software developer, including FEA and
CFD. I'll actually be using Code Aster, an open source FEA code that
runs under Linux.

	Sorry if I sound narky, but compilers is the subject at hand, not how
to write FEA code.

	Anyway, thanks for answering,

		Andrew

Re: [gentoo-user] Re: Changing compilers

[Andrew Lowe]

On 03/19/12 17:39, Nikos Chantziaras wrote:
> On 19/03/12 07:26, Andrew Lowe wrote:
>> Hi all,
>> Has anyone played around with the various "better known" compilers on
[snip]
...
...
[snip]
> 
> You don't need to "change" compilers.  You can use whatever one you like
> to build your program.  The compiler portage uses to build its packages
> does not affect your own usage of the others.
> 
> As for the fastest one, I can only speak for Intel CPUs where Intel C++
> gives me the fastest binaries.
> 
> 
> 
Nikos,
	Your experience with Intel is what I'm after. Aster, the FEA code I'm
going to use is not in Portage hence I will be using it's own build
system. When you've used Intel, have you just exported "CC="icc" or
something similar, as make.conf won't be used? Also, I've read somewhere
that there are libraries that you have to link against that are specific
to the Intel compiler as it does not create libraries that are
comparable with the gcc produced ones - is this true or does the
compiler now "play well" with the gcc world?

	Any thoughts,

		Andrew

Re: [gentoo-user] Changing compilers

[Andrew Lowe]

On 03/19/12 22:02, Michael Mol wrote:
> On Mon, Mar 19, 2012 at 8:32 AM, Mark Knecht <markknecht@gmail.com> wrote:
>> On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe <agl@wht.com.au> wrote:
>>> Hi all,
>>>    Has anyone played around with the various "better known" compilers on
>>> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
>>> situation is that I've just started my PhD which requires me to do Finite
>>> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
>>> find the "best" compiler for the job. Before anyone says "Why bother, XXX
>>> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
>>> doing this 1 - 2% IS important.
>>>
>>> What I'm looking for is any feedback people may have on ability to compile
>>> the Gentoo environment, the ability to change compilers easily, gcc-config
>>> or flags in make.conf, as to whether the compiler/linker can use the
>>> libraries as compiled by gcc on a "standard" gentoo install and so on.
>>> Obviously there is much web trawling to be done to find what other people
>>> are saying as well.
>>>
>>> Any thoughts, greatly appreciated,
>>>       Andrew Lowe
>>>
>>>
>>
>> Think CUDA
> 
> Yes. And as a convenient side-effect, it offers a great excuse to
> upgrade your video card with some regularity. The performance of
> mid-grade and high-grade video cards continues to improve rapidly.
> 

	Sorry, can't do that, I'm using epic,

http://tinyurl.com/83l5o3z

which currently ranks at 151 in the top 500 list :) It's amazing how
fast this list changes, 6 months ago, this machine was at 107 and 6
months before that 87.

	Andrew

Re: [gentoo-user] Changing compilers

[Michael Mol]

On Mon, Mar 19, 2012 at 10:05 AM, Andrew Lowe <agl@wht.com.au> wrote:
> On 03/19/12 20:34, Mark Knecht wrote:
>> On Mon, Mar 19, 2012 at 5:32 AM, Mark Knecht <markknecht@gmail.com> wrote:
>>> On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe <agl@wht.com.au> wrote:
>>>> Hi all,
>>>>    Has anyone played around with the various "better known" compilers on
>>>> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
>>>> situation is that I've just started my PhD which requires me to do Finite
>>>> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
>>>> find the "best" compiler for the job. Before anyone says "Why bother, XXX
>>>> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
>>>> doing this 1 - 2% IS important.
>>>>
>>>> What I'm looking for is any feedback people may have on ability to compile
>>>> the Gentoo environment, the ability to change compilers easily, gcc-config
>>>> or flags in make.conf, as to whether the compiler/linker can use the
>>>> libraries as compiled by gcc on a "standard" gentoo install and so on.
>>>> Obviously there is much web trawling to be done to find what other people
>>>> are saying as well.
>>>>
>>>> Any thoughts, greatly appreciated,
>>>>       Andrew Lowe
>>>>
>>>>
>>>
>>> Think CUDA
>>>
>>> Mark
>>
>> Sorry. Meant to include this reference: <$15 on Kindle. Reads great on
>> Kindle for PC.
>>
>> http://www.amazon.com/CUDA-Example-Introduction-General-Purpose-ebook/dp/B003VYBOSE/ref=sr_1_4?ie=UTF8&qid=1332160431&sr=8-4
>>
>>
>
>        I'm sorry but I'm doing a PhD, not creating a career in Academia. The
> concept of writing an FEA or CFD from scratch, with CUDA is laughable, I
> just don't have the time to learn CUDA, research the field, small
> displacement, large displacement, dynamics, material nonlinearities,
> write the code, and then most importantly benchmark it to make sure it's
> actually correct. This is all bearing in mind that I have 20+ years
> experience as a C/C++ technical software developer, including FEA and
> CFD. I'll actually be using Code Aster, an open source FEA code that
> runs under Linux.
>
>        Sorry if I sound narky, but compilers is the subject at hand, not how
> to write FEA code.

If you really care about a 1-2% difference, you should not be
dismissing GPGPU-accelerated code so easily! If the tools you seem to
have already settled on don't support it, you should either use
different tools, or correct the ones you're working with.

The lead Python guy had an astute observation (which I'll generalize)
the other day; for 99% of your program, it doesn't matter what
programming language you use. For the 1% where you need speed, you
should call out into the faster language.

-- 
:wq

Re: [gentoo-user] Changing compilers

[Michael Mol]

On Mon, Mar 19, 2012 at 10:18 AM, Andrew Lowe <agl@wht.com.au> wrote:
> On 03/19/12 22:02, Michael Mol wrote:
>> On Mon, Mar 19, 2012 at 8:32 AM, Mark Knecht <markknecht@gmail.com> wrote:
>>> On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe <agl@wht.com.au> wrote:
>>>> Hi all,
>>>>    Has anyone played around with the various "better known" compilers on
>>>> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
>>>> situation is that I've just started my PhD which requires me to do Finite
>>>> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
>>>> find the "best" compiler for the job. Before anyone says "Why bother, XXX
>>>> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
>>>> doing this 1 - 2% IS important.
>>>>
>>>> What I'm looking for is any feedback people may have on ability to compile
>>>> the Gentoo environment, the ability to change compilers easily, gcc-config
>>>> or flags in make.conf, as to whether the compiler/linker can use the
>>>> libraries as compiled by gcc on a "standard" gentoo install and so on.
>>>> Obviously there is much web trawling to be done to find what other people
>>>> are saying as well.
>>>>
>>>> Any thoughts, greatly appreciated,
>>>>       Andrew Lowe
>>>>
>>>>
>>>
>>> Think CUDA
>>
>> Yes. And as a convenient side-effect, it offers a great excuse to
>> upgrade your video card with some regularity. The performance of
>> mid-grade and high-grade video cards continues to improve rapidly.
>>
>
>        Sorry, can't do that, I'm using epic,
>
> http://tinyurl.com/83l5o3z
>
> which currently ranks at 151 in the top 500 list :) It's amazing how
> fast this list changes, 6 months ago, this machine was at 107 and 6
> months before that 87.

That does change things a bit. I don't know Epic's structure or their
upgrade plans, but if you're confident it's not going to have GPGPU
capabilities, then CUDA and OpenCL are less useful for you. OpenCL, at
least, still handles per-CPU and per-node job dispatching, though. And
that's still likely to be useful for performing on huge matrices.

To answer your original question: No, I haven't done much with
anything other than gcc on Gentoo. What you *should* do is grab each
compiler (trial versions, if necessary) and test them to find which
gives you the best results. It's my understanding PhD programs involve
getting things done right, not so much quickly or easily. Best to be
methodical about it.

-- 
:wq

Re: [gentoo-user] Re: Changing compilers

[Florian Philipp]

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Am 19.03.2012 15:11, schrieb Andrew Lowe:
> On 03/19/12 17:39, Nikos Chantziaras wrote:
>> On 19/03/12 07:26, Andrew Lowe wrote:
>>> Hi all,
>>> Has anyone played around with the various "better known" compilers on
> [snip]
> ...
> ...
> [snip]
>>
>> You don't need to "change" compilers.  You can use whatever one you like
>> to build your program.  The compiler portage uses to build its packages
>> does not affect your own usage of the others.
>>
>> As for the fastest one, I can only speak for Intel CPUs where Intel C++
>> gives me the fastest binaries.
>>
>>
>>
> Nikos,
> 	Your experience with Intel is what I'm after. Aster, the FEA code I'm
> going to use is not in Portage hence I will be using it's own build
> system. When you've used Intel, have you just exported "CC="icc" or
> something similar, as make.conf won't be used? Also, I've read somewhere
> that there are libraries that you have to link against that are specific
> to the Intel compiler as it does not create libraries that are
> comparable with the gcc produced ones - is this true or does the
> compiler now "play well" with the gcc world?
> 
> 	Any thoughts,
> 
> 		Andrew
> 

Look here:
http://en.gentoo-wiki.com/wiki/Intel_C%2B%2B_Compiler

Regards,
Florian Philipp


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[gentoo-user] Re: Changing compilers

[James]

Andrew Lowe <agl <at> wht.com.au> writes:


>      Has anyone played around with the various "better known"  
> compilers on Gentoo? By "better known", I'm referring to gcc, Intel,  
> llvm, pathscale. My situation is that I've just started my PhD which  
> requires me to do Finite Element Analysis, FEA, and Computational  
> Fluid Dynamics, CFD, and I want to find the "best" compiler for the  
> job. Before anyone says "Why bother, XXX compiler is only 1 - 2%  
> faster than gcc", in the context of the work I'm doing this 1 - 2% IS  
> important.


"Octave" is in portage, as it is a matlab sorta package for
fluids.

google for

Octave : Computational Fluid Dynamics : Finite Element Analysis

for starters.

I understand you are smart, but why push the issues on compiler
efficiency, if you are not willing to hack the compiler code?

Why not push the mathematical envelop and use:
Sparse Matrix Techniques ??????????????????????

http://www.cise.ufl.edu/research/sparse/matrices/

http://blogs.mathworks.com/loren/2007/03/01/
creating-sparse-finite-element-matrices-in-matlab/


hth,

James

Re: [gentoo-user] Changing compilers

[Mark Knecht]

On Mon, Mar 19, 2012 at 7:05 AM, Andrew Lowe <agl@wht.com.au> wrote:
> On 03/19/12 20:34, Mark Knecht wrote:
>> On Mon, Mar 19, 2012 at 5:32 AM, Mark Knecht <markknecht@gmail.com> wrote:
>>> On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe <agl@wht.com.au> wrote:
>>>> Hi all,
>>>>    Has anyone played around with the various "better known" compilers on
>>>> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
>>>> situation is that I've just started my PhD which requires me to do Finite
>>>> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
>>>> find the "best" compiler for the job. Before anyone says "Why bother, XXX
>>>> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
>>>> doing this 1 - 2% IS important.
>>>>
>>>> What I'm looking for is any feedback people may have on ability to compile
>>>> the Gentoo environment, the ability to change compilers easily, gcc-config
>>>> or flags in make.conf, as to whether the compiler/linker can use the
>>>> libraries as compiled by gcc on a "standard" gentoo install and so on.
>>>> Obviously there is much web trawling to be done to find what other people
>>>> are saying as well.
>>>>
>>>> Any thoughts, greatly appreciated,
>>>>       Andrew Lowe
>>>>
>>>>
>>>
>>> Think CUDA
>>>
>>> Mark
>>
>> Sorry. Meant to include this reference: <$15 on Kindle. Reads great on
>> Kindle for PC.
>>
>> http://www.amazon.com/CUDA-Example-Introduction-General-Purpose-ebook/dp/B003VYBOSE/ref=sr_1_4?ie=UTF8&qid=1332160431&sr=8-4
>>
>>
>
>        I'm sorry but I'm doing a PhD, not creating a career in Academia. The
> concept of writing an FEA or CFD from scratch, with CUDA is laughable, I
> just don't have the time to learn CUDA, research the field, small
> displacement, large displacement, dynamics, material nonlinearities,
> write the code, and then most importantly benchmark it to make sure it's
> actually correct. This is all bearing in mind that I have 20+ years
> experience as a C/C++ technical software developer, including FEA and
> CFD. I'll actually be using Code Aster, an open source FEA code that
> runs under Linux.
>
>        Sorry if I sound narky, but compilers is the subject at hand, not how
> to write FEA code.
>
>        Anyway, thanks for answering,
>
>                Andrew
>

Nahh, be as snarky as you like as long as you don't really mean it personally.

My experience with CUDA, and I'm not a programmer, is that there is a
fairly steep learning curve. However changing C compilers will get you
maybe 5%. Changing to CUDA will get you 30,000%, assuming a mid-high
range CUDA card and that you can parallel-ize FEA. I did a little
Googling and it seems that FEA is a pretty common CUDA topic so I
don't think at the outset that you'd find yourself all alone.

Good luck whatever you do and know that I didn't mind the response at all! :-)

Cheers,
Mark

Re: [gentoo-user] Changing compilers

[Andrew Lowe]

On 03/20/12 00:03, Mark Knecht wrote:
> On Mon, Mar 19, 2012 at 7:05 AM, Andrew Lowe <agl@wht.com.au> wrote:
>> On 03/19/12 20:34, Mark Knecht wrote:
>>> On Mon, Mar 19, 2012 at 5:32 AM, Mark Knecht <markknecht@gmail.com> wrote:
>>>> On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe <agl@wht.com.au> wrote:
>>>>> Hi all,
>>>>>    Has anyone played around with the various "better known" compilers on
>>>>> Gentoo? By "better known", I'm referring to gcc, Intel, llvm, pathscale. My
>>>>> situation is that I've just started my PhD which requires me to do Finite
>>>>> Element Analysis, FEA, and Computational Fluid Dynamics, CFD, and I want to
>>>>> find the "best" compiler for the job. Before anyone says "Why bother, XXX
>>>>> compiler is only 1 - 2% faster than gcc", in the context of the work I'm
>>>>> doing this 1 - 2% IS important.
>>>>>
>>>>> What I'm looking for is any feedback people may have on ability to compile
>>>>> the Gentoo environment, the ability to change compilers easily, gcc-config
>>>>> or flags in make.conf, as to whether the compiler/linker can use the
>>>>> libraries as compiled by gcc on a "standard" gentoo install and so on.
>>>>> Obviously there is much web trawling to be done to find what other people
>>>>> are saying as well.
>>>>>
>>>>> Any thoughts, greatly appreciated,
>>>>>       Andrew Lowe
>>>>>
>>>>>
>>>>
>>>> Think CUDA
>>>>
>>>> Mark
>>>
>>> Sorry. Meant to include this reference: <$15 on Kindle. Reads great on
>>> Kindle for PC.
>>>
>>> http://www.amazon.com/CUDA-Example-Introduction-General-Purpose-ebook/dp/B003VYBOSE/ref=sr_1_4?ie=UTF8&qid=1332160431&sr=8-4
>>>
>>>
>>
>>        I'm sorry but I'm doing a PhD, not creating a career in Academia. The
>> concept of writing an FEA or CFD from scratch, with CUDA is laughable, I
>> just don't have the time to learn CUDA, research the field, small
>> displacement, large displacement, dynamics, material nonlinearities,
>> write the code, and then most importantly benchmark it to make sure it's
>> actually correct. This is all bearing in mind that I have 20+ years
>> experience as a C/C++ technical software developer, including FEA and
>> CFD. I'll actually be using Code Aster, an open source FEA code that
>> runs under Linux.
>>
>>        Sorry if I sound narky, but compilers is the subject at hand, not how
>> to write FEA code.
>>
>>        Anyway, thanks for answering,
>>
>>                Andrew
>>
> 
> Nahh, be as snarky as you like as long as you don't really mean it personally.
> 
> My experience with CUDA, and I'm not a programmer, is that there is a
> fairly steep learning curve. However changing C compilers will get you
> maybe 5%. Changing to CUDA will get you 30,000%, assuming a mid-high
> range CUDA card and that you can parallel-ize FEA. I did a little
> Googling and it seems that FEA is a pretty common CUDA topic so I
> don't think at the outset that you'd find yourself all alone.
> 
> Good luck whatever you do and know that I didn't mind the response at all! :-)
> 
> Cheers,
> Mark
> 
> 

	The thing is that I agree that CUDA is the way to go for things like
FEA & CFD, in fact the mob that runs the super computer I'm using is
installing another one that is top heavy in CUDA cards. But the thing is
as I'm using the FEA as a tool, rather than playing around with the
innards of the code, I need an established code, one that has
verification behind it. My topic looks at the way that steel connections
behave so I need an established FEA code that is verified to provide the
correct answers, I don't get that if I write my own code.

	Most likely I'll write a short paper covering a comparison of existing
C/C++ compilers and their relative speeds, spend the next 18 months - 2
years doing my research and then to close things off, I'll probably be
able to write another short paper concerning CUDA speedups as the FEA
code bases will have caught up and been verified.

	Thanks for peoples replies,

		Andrew

p.s. Writing this I just had a sudden horrific though and checked the
FEA code I'm using, Aster. It's written mostly in FORTRAN - fat chance
I'm going to be hacking that code........

[gentoo-user] Re: Changing compilers

[Nikos Chantziaras]

On 19/03/12 16:11, Andrew Lowe wrote:
> On 03/19/12 17:39, Nikos Chantziaras wrote:
>> On 19/03/12 07:26, Andrew Lowe wrote:
>>> Hi all,
>>> Has anyone played around with the various "better known" compilers on
> [snip]
> ...
> ...
> [snip]
>>
>> You don't need to "change" compilers.  You can use whatever one you like
>> to build your program.  The compiler portage uses to build its packages
>> does not affect your own usage of the others.
>>
>> As for the fastest one, I can only speak for Intel CPUs where Intel C++
>> gives me the fastest binaries.
>>
>>
>>
> Nikos,
> 	Your experience with Intel is what I'm after. Aster, the FEA code I'm
> going to use is not in Portage hence I will be using it's own build
> system. When you've used Intel, have you just exported "CC="icc" or
> something similar, as make.conf won't be used? Also, I've read somewhere
> that there are libraries that you have to link against that are specific
> to the Intel compiler as it does not create libraries that are
> comparable with the gcc produced ones - is this true or does the
> compiler now "play well" with the gcc world?

No special libs required.  The binaries I get (both C and C++) don't use 
anything extra.  I checked both with "ldd" as well as with lsof at 
runtime (in case it dlopens anything).

For building, you use "CC=icc" and "CXX=icpc" for regular makefiles or 
autoconf scripts.  I mostly use qmake though (I use Qt for my GUIs).  In 
that case, you call qmake like this:

   qmake -spec linux-icc

and it creates a makefile that will use ICC.  This is also an example of 
ICC using C and C++ libs (Qt is C++) that were built by GCC without 
issues; its ABI is fully GCC compatible.

There are way to use ICC for portage too.  I tried that once.  It worked 
quite well.  But I didn't went with it since too much of a bother.

Note that the link Florian posted is a bit outdated.  For example the 
sections that tells you that "binaries compiled with icc won't work 
after icc is uninstalled" is not true.  They will work just fine.  The 
exception of course if when you specifically use an ICC library, like 
the Intel math kernel library.

Re: [gentoo-user] Re: Changing compilers

[Andrew Lowe]

On 03/20/12 01:17, Nikos Chantziaras wrote:
> On 19/03/12 16:11, Andrew Lowe wrote:
>> On 03/19/12 17:39, Nikos Chantziaras wrote:
>>> On 19/03/12 07:26, Andrew Lowe wrote:
>>>> Hi all,
>>>> Has anyone played around with the various "better known" compilers on
>> [snip]
>> ...
>> ...
>> [snip]
>>>
>>> You don't need to "change" compilers.  You can use whatever one you like
>>> to build your program.  The compiler portage uses to build its packages
>>> does not affect your own usage of the others.
>>>
>>> As for the fastest one, I can only speak for Intel CPUs where Intel C++
>>> gives me the fastest binaries.
>>>
>>>
>>>
>> Nikos,
>>     Your experience with Intel is what I'm after. Aster, the FEA code I'm
>> going to use is not in Portage hence I will be using it's own build
>> system. When you've used Intel, have you just exported "CC="icc" or
>> something similar, as make.conf won't be used? Also, I've read somewhere
>> that there are libraries that you have to link against that are specific
>> to the Intel compiler as it does not create libraries that are
>> comparable with the gcc produced ones - is this true or does the
>> compiler now "play well" with the gcc world?
> 
> No special libs required.  The binaries I get (both C and C++) don't use
> anything extra.  I checked both with "ldd" as well as with lsof at
> runtime (in case it dlopens anything).
> 
> For building, you use "CC=icc" and "CXX=icpc" for regular makefiles or
> autoconf scripts.  I mostly use qmake though (I use Qt for my GUIs).  In
> that case, you call qmake like this:
> 
>   qmake -spec linux-icc
> 
> and it creates a makefile that will use ICC.  This is also an example of
> ICC using C and C++ libs (Qt is C++) that were built by GCC without
> issues; its ABI is fully GCC compatible.
> 
> There are way to use ICC for portage too.  I tried that once.  It worked
> quite well.  But I didn't went with it since too much of a bother.
> 
> Note that the link Florian posted is a bit outdated.  For example the
> sections that tells you that "binaries compiled with icc won't work
> after icc is uninstalled" is not true.  They will work just fine.  The
> exception of course if when you specifically use an ICC library, like
> the Intel math kernel library.
> 
> 
> 
	Thanks for that. The library question was the reason I didn't proceed
with playing around with icc ages ago. Your experience tells me it's now
rectified.

	Andrew

[gentoo-user] Re: Changing compilers

[Nikos Chantziaras]

On 19/03/12 19:24, Andrew Lowe wrote:
> On 03/20/12 01:17, Nikos Chantziaras wrote:
>> On 19/03/12 16:11, Andrew Lowe wrote:
>>> On 03/19/12 17:39, Nikos Chantziaras wrote:
>>>> On 19/03/12 07:26, Andrew Lowe wrote:
>>>>> Hi all,
>>>>> Has anyone played around with the various "better known" compilers on
>>> [snip]
>>> ...
>>> ...
>>> [snip]
>>>>
>>>> You don't need to "change" compilers.  You can use whatever one you like
>>>> to build your program.  The compiler portage uses to build its packages
>>>> does not affect your own usage of the others.
>>>>
>>>> As for the fastest one, I can only speak for Intel CPUs where Intel C++
>>>> gives me the fastest binaries.
>>>>
>>> [...] Also, I've read somewhere
>>> that there are libraries that you have to link against that are specific
>>> to the Intel compiler as it does not create libraries that are
>>> comparable with the gcc produced ones - is this true or does the
>>> compiler now "play well" with the gcc world?
>>
>> No special libs required.  The binaries I get (both C and C++) don't use
>> anything extra.  I checked both with "ldd" as well as with lsof at
>> runtime (in case it dlopens anything).
>>  [...]
> 	Thanks for that. The library question was the reason I didn't proceed
> with playing around with icc ages ago. Your experience tells me it's now
> rectified.

Just to verify that I'm not mistaken about this, I just compiled a 
non-trivial project that uses C++ libraries, then uninstalled icc and 
all its deps (with --depclean), and the binary still ran without issues.

Re: [gentoo-user] Changing compilers

[Andrew Lowe]

On 19/03/2012 10:18 PM, Andrew Lowe wrote:
> On 03/19/12 22:02, Michael Mol wrote:
>> On Mon, Mar 19, 2012 at 8:32 AM, Mark Knecht<markknecht@gmail.com>  wrote:
>>> On Sun, Mar 18, 2012 at 10:26 PM, Andrew Lowe<agl@wht.com.au>  wrote:
>>>> Hi all,
[snip]
...
...
[snip]
>
> which currently ranks at 151 in the top 500 list :) It's amazing how
> fast this list changes, 6 months ago, this machine was at 107 and 6
> months before that 87.
>
> 	Andrew

	Just in closing on this subject, thanks to those who responded, have a 
quick look at this page from the llvm/clang project:

http://clang.llvm.org/diagnostics.html

For my non FEA/CFD programming, I don't care if clang is 5 - 10% slower 
than gcc, the diagnostic output that clang produces looks to be 
"spectacular" in comparison to gcc and will be enough for me to dump gcc 
and shift to clang.

	Andrew

Re: [gentoo-user] Changing compilers

[Walter Dnes]

On Mon, Mar 19, 2012 at 02:00:18PM +0800, Andrew Lowe wrote

> I'm looking for the faster code, the run time to be faster - I compile  
> the FEA & CFD code once but will be running many jobs.
> 
> Andrew

  Since you're asking on the Gentoo list, can I safely assume you use
Gentoo?  Gentoo gives *MUCH MORE* than 1% or 2% improvement, *IF YOU
OPTIMIZE PROPERLY*.  This does not mean going into "Gentoo-ricer"
territory, but it does mean using the features of Gentoo to their
fullest.  Gentoo allows you to build binaries with gcc that are tuned to
*YOUR* cpu.  The advantage is that it gets the maximum out of your cpu.
The disadvantage is that a binary compiled for a newer cpu will probably
not run on an older cpu on another machine.  In your /etc/make/conf, I
recommend...

CFLAGS="-O2 -march=native -mfpmath=sse -fomit-frame-pointer -pipe"
CXXFLAGS="${CFLAGS}"
MAKEOPTS="-j1"

  The "-march=native" setting tells gcc to build binaries to use all the
cpu's available features.  The CXXFLAGS variable is specific to C++.
Set it identical to CFLAGS, so that C++ code gets the same settings.
The MAKEOPTS="-j1" setting slows down the build process slightly, but it
does *NOT* affect the final binary.  It does avoid some occasional
mysterious hard-to-reproduce errors that stop builds dead in their
tracks.  The first time you bang your head against the wall for a couple
of hours trying to figure out the problem, you'll waste more time than
you've saved with a higher numbered "j" value.

  Note also that if you've done a recent fresh install, you should...
* emerge system
* emerge world
* rebuild the kernel entirely and reboot
...in that order.  The binaries from the install CD are generic i686 (32
bit) or amd64 (64 bit) with no optional machine instructions selected..
They have to be this way to install properly on 8-year-old machines.
But this doesn't take advantage of the faster instructions on newer
machines.  The following is a true story that happened to me, not a
friend-of-a-friend.  I have a 4 1/2 year old Dell with an onboard Intel
GPU.  Right after the install, it could not keep up with 1080i video
from my TV tuner box, or even teh slowest speed for NHL GameCenter Live.
After emerging system+world and rebuilding, the same machine was able to
view 1080i TV and run the low-bandwidth version of NHL GameCenter Live.
That is a very significat difference.

  Note that merely optimizing the program itself isn't enough.  The
binary is dynamically linked to various math libraries.  The program
reads data from and writes output to disk.  And there are always kernel
calls along the way.  So optimizing every math library, disk I/O code,
and kernel code contributes to faster execution.

-- 
Walter Dnes <waltdnes@waltdnes.org>