Re: [Users] intel compiler flags?

[Jonah Miller]

Hi Roland, Frank,

Thanks very much. This was exactly what I was looking for.

Best,
Jonah

On 15-11-11 04:46 AM, Roland Haas wrote:
> Hello all,
>
> uhh, let me actually read the question. Frank seems to have pointed you
> to what I assume (have not checked yet) to be the proper documentation
> that shows what can go wrong. Now for how I worked around the issues myself:
>
> For the symmetric operators branch I use -fp-model precise to the intel
> compiler eg on zwicky I use the default zwicky machine defintion file in
> simfactory then add "-fp-model precise" to all CFLAGS/CXXFLAGS/F90FLAGS
> so that they read:
>
> C_OPTIMISE_FLAGS   = -O2 -xHost -fp-model precise
> CXX_OPTIMISE_FLAGS = -O2 -xHost -fp-model precise
> F77_OPTIMISE_FLAGS = -O2 -xHost -fp-model precise
> F90_OPTIMISE_FLAGS = -O2 -xHost -fp-model precise
>
> for the gnu compiler on bluewaters I had to also disable some
> optimizations (I don't know why):
>
> C_OPTIMISE_FLAGS = -O3 -fno-expensive-optimizations -fno-ipa-cp-clone
>
> @Jonah: if you have access to the SXS wiki (say due to Spectre work),
> you can find this information on
> https://www.black-holes.org/wiki/center_of_mass_conserving_setup
> somewhere under the first big table.
>
> Yours,
> Roland
>
>
> On 2015-11-10 22:47, Erik Schnetter wrote:
>> Roland, I think you have been using such flags. Which flags exactly did you
>> use?
>>
>> -erik
>>
>> On Tue, Nov 10, 2015 at 1:45 PM, Frank Loeffler  wrote:
>>
>>> On Tue, Nov 10, 2015 at 01:38:08PM -0500, Jonah Miller wrote:
 I am working on developing a modified stencil for the Einstein Toolkit
 and I am discovering that regression tests pass when I use the GNU
 compilers but fail when I use the Intel compilers, even with gentle
 optimization settings such as -O1. I suspect over-zealous optimization.
 Has anyone encountered this sort of problem before? And if so, does
 anybody know a good combination of flags that makes the intel compiler
 more cautious, without sacrificing too much speed? (For example,
 disabling fast math, which seems to be set to active by default.)
>>> The default for the Intel compiler is non-exact math. Try some of the
>>> options mentioned here:
>>>
>>>
>>> https://software.intel.com/en-us/articles/consistency-of-floating-point-results-using-the-intel-compiler
>>>
>>> How much that influences effective speed likely depends a lot on your
>>> code.
>>>
>>> Frank
>>>
>>>
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>>
>>
>>
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Re: [Users] intel compiler flags?

[Frank Loeffler]

On Tue, Nov 10, 2015 at 01:38:08PM -0500, Jonah Miller wrote:
> I am working on developing a modified stencil for the Einstein Toolkit 
> and I am discovering that regression tests pass when I use the GNU 
> compilers but fail when I use the Intel compilers, even with gentle 
> optimization settings such as -O1. I suspect over-zealous optimization. 
> Has anyone encountered this sort of problem before? And if so, does 
> anybody know a good combination of flags that makes the intel compiler 
> more cautious, without sacrificing too much speed? (For example, 
> disabling fast math, which seems to be set to active by default.)

The default for the Intel compiler is non-exact math. Try some of the
options mentioned here:

https://software.intel.com/en-us/articles/consistency-of-floating-point-results-using-the-intel-compiler

How much that influences effective speed likely depends a lot on your
code.

Frank



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Re: [Users] intel compiler flags?

[Erik Schnetter]

Roland, I think you have been using such flags. Which flags exactly did you
use?

-erik

On Tue, Nov 10, 2015 at 1:45 PM, Frank Loeffler  wrote:

> On Tue, Nov 10, 2015 at 01:38:08PM -0500, Jonah Miller wrote:
> > I am working on developing a modified stencil for the Einstein Toolkit
> > and I am discovering that regression tests pass when I use the GNU
> > compilers but fail when I use the Intel compilers, even with gentle
> > optimization settings such as -O1. I suspect over-zealous optimization.
> > Has anyone encountered this sort of problem before? And if so, does
> > anybody know a good combination of flags that makes the intel compiler
> > more cautious, without sacrificing too much speed? (For example,
> > disabling fast math, which seems to be set to active by default.)
>
> The default for the Intel compiler is non-exact math. Try some of the
> options mentioned here:
>
>
> https://software.intel.com/en-us/articles/consistency-of-floating-point-results-using-the-intel-compiler
>
> How much that influences effective speed likely depends a lot on your
> code.
>
> Frank
>
>
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>


-- 
Erik Schnetter 
http://www.perimeterinstitute.ca/personal/eschnetter/
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