Re: Similar systems, different performance of fortran code
On Thu, 2005-04-21 at 20:35 +0900, Victor Munoz wrote:
> To add more information about this:
>
> I did a time profiling with gprof. The most important changes:
>
> woody:
> time seconds seconds calls s/call s/call name
> 96.79 13.88 13.88 482 0.03 0.03 move_
> 0.28 14.16 0.04 482 0.00 0.00 cpft_
> 0.21 14.23 0.03 241 0.00 0.00 fields_
>
> sid:
>
> time seconds seconds calls s/call s/call name
> 99.25 107.86 107.86 482 0.22 0.22 move_
> 0.58 108.49 0.63 241 0.00 0.00 fields_
> 0.06 108.56 0.07 482 0.00 0.00 cpft_
>
> So there is a huge difference in the subroutines move and fields. But move,
> for instance, is not very involved. It's a subroutine which calls no other
> functions, just defines some variables, "common" lines, and such,
> and then iterates on the particles to move them. A series of matrices
> containing data for the particles are accessed element by element,
> divided by scalars, summed, etc. Nothing exotic. But these lines are the most
> often executed lines in the code, and are probably causing this huge
> difference in performance. But it's not obvious (to me at least) why...
>
> Regards,
>
> Victor
>
I've deleted your original email with info on the diff systems, but it
sounds like 'move' may have to allocate/access substantial amounts of
memory. Do you have the same amount of cache on each processor? Do you
notice increase in diff in times as you increase size of matrices in
'move'? Do you have the same amount (and speed of) available mem on both
machines? And, if they are reading are the HDs the same speed/cache size
etc? You may want to delve into 'move' line by line to see which takes
the longest...
M
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