20051007, 15:15  #45 
Sep 2002
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23×179 Posts 
Thomas informs me that the FFT boundaries have changed recently with the latest LLRs for Athlons:
Here are the latest Athlon FFT lengths for k=3: fftlen nmax  114688 2233110 131072 2560126 163840 3180158 196608 3777190 229376 4411222 262144 5056254  So it makes sense to use a older version of LLR to do n=22331112244110 This would be about 600 tests, saving 2000 secs per test = 2 cpu weeks We'll sort it out when the next set of numbers are released (n>2.2 million) Thanks Thomas 
20051008, 14:38  #46 
Feb 2003
780_{16} Posts 
Meanwhile I had some additional tests on the Athlon, using LLR 3.5, 3.6, and 3.6.2.
As Paul already mentioned in the above post, the FFT boundaries are slightly lower for the latest LLR versions (3.6 and 3.6.2), e.g. for the current 112k FFT we have nmax=2233110 for versions 3.6/3.6.2, but nmax=2244110 for version 3.5. Below are some timings using the different LLR's on my 2GHz Athlon: Code:
Athlon 2GHz (2400+)  times per iteration for FFT lengths 114688 (112k) and 131072 (128k): LLR 112k 128k  3.5 7.024 7.904 3.6 7.045 7.938 3.6.2 7.042 7.944  (1) There is no significant difference between LLR 3.6 and 3.6.2. (2) LLR 3.5 is slightly faster than 3.6/3.6.2 (about 0.30.5%). The latter holds only for the Athlon. On the P4, versions 3.6/3.6.2 are about 1.52% faster than LLR 3.5 (at least on my machines...). If someone else (perhaps, or at least you, Paul ) would verify that LLR 3.5 is still a bit faster (or at least not slower) than versions 3.6/3.6.2 on your Athlons, we could recommend to use LLR 3.5 exclusively and entirely for the Athlon, e.g. not only for n=22331112244110, but for any range. For those of you, who want to do the timings, I suggest to use the following n's: 2233110 and 2233111, or 2244110 and 2244111, depending on the LLR version. Set the screen output to "every 1000 iterations" and watch it for about one minute. Note, that the very first output on your screen shows a larger msecs/iteration due to the initial U0/V0 computations. And now let's find that twomegabit prime! 
20051008, 23:52  #47 
Sep 2002
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23×179 Posts 
I have timed "llr35" and "llr362" on an Athlon (Debian+X) and calculated that the old LLR is 0.4% quicker:
7.912 ms/iteration llr362 7.880 ms/iteration llr35 
20051009, 00:28  #48 
Sep 2002
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23·179 Posts 
Some more timings on Linux with no X:
Athlon 1050MHz 13.014 ms/iteration llr362 13.028 ms/iteration llr35 ...new LLR slightly faster (0.1%) Athlon XP1600+ 9.432 ms/iteration llr362 9.401 ms/iteration llr35 ...old LLR faster (0.3%) Athlon XP2000+ 8.278 ms/iteration llr362 8.250 ms/iteration llr35 ...old LLR faster (0.3%) So it seems on AthlonXPs (not ordinary old Athlons) it is better to run LLR35 Last fiddled with by paulunderwood on 20051009 at 00:51 
20070214, 10:17  #49 
Feb 2003
2^{7}×3×5 Posts 
Just out of curiosity I did a test on an Opteron 246 (2 GHz) using the "CpuSupportsSSE2=0" switch to see whether it would run faster at the lower FFT length. Here are the figures I got:
Code:
FFT length time per iteration  SSE2 enabled: 196608 8.483 ms SSE2 disabled: 163840 9.036 ms Last fiddled with by Thomas11 on 20070214 at 10:18 
20080616, 17:32  #50 
Sep 2002
Database er0rr
23×179 Posts 
IBDWT break points for 5M < n < 20M+
Thanks to Thomas for this info:
here are the FFT lengths and break points for k=3, n=520M: Code:
For P4 and other SSE2 cpus: fftlen nmax  327680 6161318 393216 7339382 458752 8544446 524288 9764510 655360 12130637 786432 14446765 917504 16822893 1048576 19219021 1310720 23891277 And for Athlons (cpus without SSE2): fftlen nmax  262144 5056254 327680 6285318 393216 7460382 458752 8707446 524288 9964510 655360 12370637 786432 14686765 917504 17162893 1048576 19629021 1310720 24351277 
20080626, 14:17  #51  
Sep 2002
Database er0rr
23×179 Posts 
By request and by curtesy of Thomas here is the program to create tables such as above.
Quote:
Last fiddled with by paulunderwood on 20080626 at 14:17 

20080626, 15:56  #52 
Sep 2002
Database er0rr
4117_{10} Posts 
Here is another program written by Thomas for optimization of project throughput, for wide ranges of "n" crossing FFT jumps.
