[Radiance-general] compiling Radiance 64-bit?

[James Lee]

On 04/05/06, 11:56:00, Axel Jacobs <a.jacobs at londonmet.ac.uk> wrote
regarding Re: [Radiance-general] compiling Radiance 64-bit?:

> > Why do you think radiance needs to be 64bit?  On both and Sparc and
> > the AMD64 the 32bit binaries ran quicker.   Only if it needs to
> > address >2G of memory does it *need* to be 64bit.  *Some* programs
> > run quicker 64 bit but *most* *don't*, combine with larger executable
> > files and increased memory usage I found radiance is best 32 bit.

> I am not sure how 'bitty' the floating point values are that RADIANCE
> calculates. If they are 64-bit long, then you can actually expect a speed
> improvement, me thinks.

People expect it but it's not so.  You can still take advantage of the
better chip architecture when using 32bit addresses.


> > It stands to reason for 64bit programs to be slower because they have
> > to use twice the memory to store memory pointers.  Ah you say, doesn't
> > 64bit mean it can use 64bit registers for other things? (Like 64bit
> > ints and 64bit doubles.)  Well nothing stops that happening in 32bit
> > mode if the chip and compilers are well designed, that's what
> > sparcv8plus+vis is all about.  32/64bit is the memory address mode
> > not the chip registers.  Some say those extra registers are only used
> > on AMD64s in 64bit mode; I say I've benchmarks radiance both ways
> > and 64 bit was not quicker.

> There are benchmarks and there are benchmarks. The only way of finding
> out wheter your particular application will benefit from going 64-bit
> is to actually test it. Which is what I've done for you.

> http://luminance.londonmet.ac.uk/pickup/rad_bench_sempron.html

You are not comparing like with like.  All you 32bit tests were done
on a i386 compatible kernel.  Try a 32bit AMD64 radiance on a kernel
optimised for the AMD64 chip.





James.