fft length changes

JPL · 2018-10-28, 09:13

why is my computer doing benchmarks from time to time, it chooses fft 4608k at 6.3ms iter and sometimes it uses fft 2668k with 3.1ms iter, why does it change that?

Uncwilly · 2018-10-28, 14:44

It is optimizing the size for speed and accuracy. Larger FFT's are slower and more accurate. Smaller are faster, but the error can add up. It is basically a rounding error. Do more digits and the rounding error is unimportant. Do fewer digit and the rounding error can have an impact. Larger exponents need larger FFT's.

Which size is best may change based upon computer usage changes during the run and other factors.

Prime95 · 2018-10-28, 17:32

Quote:

Originally Posted by JPL

why is my computer doing benchmarks from time to time, it chooses fft 4608k at 6.3ms iter and sometimes it uses fft 2668k with 3.1ms iter, why does it change that?

The faster FFT is double-checking a small exponent probably around 48 million. The slower FFT is testing a large exponent likely around 85 million.

JPL · 2018-10-28, 20:45

this are the numbers my pc has/is checked, i think the numbers are about the same length. i do not quite understand the situation. my plan is to use de amd 2700x cpu most productive. can i do any manual settings?

AMD49836103C - Verified2018-10-27 11:0927.844A0B6D567D8FC33 91.2970AMD49861841C - Verified2018-10-24 07:2224.5E5762635B105A44D 91.3441AMD49835299C - Mismatch2018-10-21 17:4022.012F77B522DBC2F__ 91.2955

JPL · 2018-11-13, 17:58

Guys, does anybody now; can i do any manual settings?

moebius · 2018-11-13, 22:12

Quote:

Originally Posted by JPL

Guys, does anybody now; can i do any manual settings?

Yes you could f.e. switch off manual the auto benchmarking in prime.txt

AutoBench=0

2018-10-28, 09:13	#1
JPL Oct 2018 3 Posts	fft length changes why is my computer doing benchmarks from time to time, it chooses fft 4608k at 6.3ms iter and sometimes it uses fft 2668k with 3.1ms iter, why does it change that?

2018-10-28, 14:44	#2
Uncwilly 6809 > 6502 """"""""""""""""""" Aug 2003 101×103 Posts 23072₈ Posts	It is optimizing the size for speed and accuracy. Larger FFT's are slower and more accurate. Smaller are faster, but the error can add up. It is basically a rounding error. Do more digits and the rounding error is unimportant. Do fewer digit and the rounding error can have an impact. Larger exponents need larger FFT's. Which size is best may change based upon computer usage changes during the run and other factors. Last fiddled with by Uncwilly on 2018-10-28 at 14:45

2018-11-13, 17:58	#5
JPL Oct 2018 3₈ Posts	Anybody ha Guys, does anybody now; can i do any manual settings?

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2018-10-28, 20:45	#4
JPL Oct 2018 3₈ Posts	this are the numbers my pc has/is checked, i think the numbers are about the same length. i do not quite understand the situation. my plan is to use de amd 2700x cpu most productive. can i do any manual settings? AMD49836103C - Verified2018-10-27 11:0927.844A0B6D567D8FC33 91.2970AMD49861841C - Verified2018-10-24 07:2224.5E5762635B105A44D 91.3441AMD49835299C - Mismatch2018-10-21 17:4022.012F77B522DBC2F__ 91.2955