[Users] compiler warning for McLachlan

[Ian Hinder]

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On 27 Sep 2011, at 14:20, Ian Hinder wrote:

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> On 27 Sep 2011, at 06:04, Frank Loeffler wrote:
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>> Hi
>> 
>> On Mon, Sep 26, 2011 at 09:08:40PM -0500, Frank Loeffler wrote:
>>> In addition, McLachlan seems to compile for a very long time and uses a
>>> lot of memory (several GB per compiler process), for the Intel compiler.
>> 
>> Actually, it makes it unusable: even one compiler process now eats above
>> 10GB of Ram, on a 8GB machine. Am I the only one with this problem? This
>> is on my workstation (numrel07) where this used to work for quite a
>> while.
> 
> Yes, McLachlan has changed.  Kranc can now select the finite difference operator based on a run-time parameter.  This eliminates the need for multiple versions of the McLachlan thorn.  You can just use ML_BSSN and set fdOrder to 2, 4, 6 or 8.  For compatibility purposes, for one release, we keep the existing thorns and set the default of fdOrder to the corresponding thorn order.  
> 
> All finite difference methods are compiled in, and selected with a switch statement in the inner loop.  This makes the inner loop much larger than it was before, which must be causing problems for the compiler (even though it should be able to tell that the separate branches of the switch statement are independent and can never be optimised together).  

I just checked, and even before combining all the FD orders into one thorn, the compilation with VECTORISE_INLINE = "yes" was slow and used a lot of memory (> 8 GB) for 8th order and multipatch with vectorisation.  The compiler memory usage does seem to have increased by combining the FD orders however.  Given that production binary black hole simulations typically use 8th order these days, I think we should just use functions for the difference operators by setting VECTORISE_INLINE = no.

- -- 
Ian Hinder
ian.hinder at aei.mpg.de

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