[Halld-offline] SIMD Troubles

[Curtis A. Meyer]

Hi Simon -

   these are such a speed up on 64-bit machines that it would be a bit
of a shame to not have them default on on those boxes. Is it worth
considering having the make scripts determine 32- or 64-bit OS and
then do the appropriate thing with the SIMD things?

     Curtis
On 3/2/11 6:08 PM, Simon Taylor wrote:
> Hi.
>
> Our suspicion is that there is an alignment problem on 32-bit systems
> with regard to the SIMD instructions;  Dave looked into this some time
> ago and it is not clear to us how to fix it.
>
> I've checked in a change to Makefile.SIMD that changes the default from
> "SIMD on" to "SIMD off".  To get the SIMD instructions, one would
> now need to do "make ENABLE_SIMD=yes".
>
> Simon
>
> Matthew Shepherd wrote:
>> Hi all,
>>
>> It seems that the BMS system doesn't properly understand our SIMD capabilities on the machines here at Indiana.  If we do a default build, then we get a segmentation fault at the first DVector2 operation.  If we build with DISABLE_SIMD=1 then this segfault is avoided.
>>
>> This seems to point to two causes:
>>
>> (1) there is a bug in the SIMD implementation of DVector2
>> (2) our machines are not capable of handling current SIMD code
>>
>> (1) seems unlikely since other people are using the code.  Assuming it is (2), how do we properly diagnose and fix it?
>>
>> -Matt
>>
>>
>>
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-- 
Prof. Curtis A. Meyer		Department of Physics
Phone:	(412) 268-2745		Carnegie Mellon University
Fax:	(412) 681-0648		Pittsburgh PA 15213-3890
cmeyer at ernest.phys.cmu.edu	http://www.curtismeyer.com/