[Users] Test failures

[Ian Hinder]

On 14 Nov 2013, at 03:56, Frank Löffler <knarf at cct.lsu.edu> wrote:

> On Thu, Nov 14, 2013 at 12:55:57AM +0100, Ian Hinder wrote:
>> This is likely due to the Exact thorn.  It also fails on Stampede.  I
>> have added an EinsteinExact version of this test, and this passes on
>> my laptop, on datura, and on stampede.  I propose we remove the Exact
>> version of this test, since the tested functionality is available in
>> EinsteinExact, and Exact is anything but…
> 
> I agree, we should remove these testsuites after the release.

Why not before the release?  It is distracting to have certain tests which fail on some machines; since we know the reason for the failures, and there are other tests which test equivalent functionality, I think we should simplify the testing process and eliminate the Exact tests which are failing for which we have EinsteinExact versions.

>> Is your workstation optionlist in simfactory? What optimisation settings are you using?
> 
> Yes. It's debian.cfg and debian-intel.cfg.
> 
>> 	-Ofast
>> 	-O3
> 
> This uses -O2 without very special options. However, it uses -xHost (to
> be general and somewhat fast). According to the man-page this defaults
> to -no-prec-div on some systems. Maybe we should add -proc-div to this
> option list.
> 
> Quote:
> 
> With some optimizations, such as -msse2 (Linux* OS) or /arch:SSE2
> (Windows* OS),  the  compiler  may  change  floating-point  division
> computations into multiplication by the reciprocal of the denominator.
> For example,  A/B  is computed as A * (1/B) to improve the speed of the
> computation.

I found this section of the manual page very confusing, but in the end interpreted it differently; i.e. that this would happen with -no-prec-div but not with -prec-div.  -prec-div is the default, and it would be very odd for the compiler to make these changes when -prec-div was set.  Can you try running one of the tests with -prec-div and with -no-prec-div to check which is being used?  There should also be a compiler option to output the effective flags that are being used.

I think -xHost should be fine, and is probably the best way to choose the CPU-specific optimisations; I don't think it changes the numerical results (but compilers can always surprise us!).

-- 
Ian Hinder
http://numrel.aei.mpg.de/people/hinder

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