Re: [Fastlibnt-devel] ssfft progress report

[Development l. f. F. <fas...@li...>]

Have you got the L1 cache size set correctly for the
G5? Isn't it 32000.

Bill.

--- Development list for FLINT
<fas...@li...> wrote:

> I've been running some profiles of some of the new
> development ssfft  
> code (in the ssfft3 branch) against the trunk
> version.
> 
> The results are a little weird. The target function
> is  
> ssfft_fft_iterative(), which is designed to handle
> L1-sized  
> transforms, using a plain iterative FFT. In
> particular it's intended  
> for use with short coefficients where bitshift
> factoring is  
> inappropriate, and small enough transforms that FFT
> factoring is not  
> necessary. I've been running it for transform
> lengths M = 16, 32, 64,  
> 128, 256, 512, 1024, with a range of truncation
> parameters, and  
> coefficient lengths n = 1, 2, 3, 4, 6, 8 limbs.
> 
> I've done profiles on sage (= sage.math), martinj (=
> jason martin's  
> machine), bsd (= william stein's xeon), and my G5.
> 
> ======== sage, martinj, bsd ========
> 
> For lengths >= 256, it is unconditonally faster than
> the old code, on  
> the above platforms (modulo a few random data
> points). The speedups  
> are typically:
> 
> sage: 5-15%
> bsd: 15-25%
> martinj: 15-25%
> 
> Some combinations get speedups of up to 40%. So this
> is great.
> 
> For lengths 64 and 128, there are a few problem
> areas, particularly  
> for n = 3, although mostly it's still ahead of the
> old code.
> 
> Length 32 and below is really a mixed bag. I find
> this surprising.  
> This code should work particularly well on small
> problems.
> 
> On the above platforms, apart from a few outliers,
> the new code was  
> never worse than 10% slower than the old code.
> 
> ======== G5 ========
> 
> On my powerpc g5 machine, things looked BAD. The new
> code is  
> typically 15-20% SLOWER than the old code. It's
> sometimes as much as  
> 10% faster, but usually it's slower.
> 
> I have absolutely no idea why this is happening.
> 
> david
> 
> 
>
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