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FFT size for factorials and primorials
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 Bur Volunteer tester
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There seem to be some versions of pfgw that support multithreading and I was wondering if it'd be worth already to look into it for current factorials/primorials in PSA.
But apparently, pfgw doesn't output the FFT size. Does anyone know it or how to get the FFT size from the respective number by other means?
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1281979 * 2^485014 + 1 is prime ... no further hits up to: n = 5,700,000 | |
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rogueVolunteer developer
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There seem to be some versions of pfgw that support multithreading and I was wondering if it'd be worth already to look into it for current factorials/primorials in PSA.
But apparently, pfgw doesn't output the FFT size. Does anyone know it or how to get the FFT size from the respective number by other means?
Use the command line switch of -V and it will print the FFT size for each test. | |
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BurVolunteer tester
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Thanks!
In case anyone else is interested:
n!+-1
n FFT
100,000 160K
250,000 448K
500,000 896K
750,000 1440K
1,000,000 1920K
1,250,000 2560K
1,500,000 3000K
1,750,000 3584K
2,000,000 4000K
n#+-1
n FFT
1,250,000 192K
1,750,000 256K
2,500,000 384K
3,000,000 448K
4,000,000 640K
5,000,000 768K
7,500,000 1120K
10,000,000 1536K
20,000,000 3000K
So it will take some years at PSA until MT might begin to make sense even on older CPUs.
pfgw also outputs the number of bits, is that actually the size on powers of two? Then it'd be easy to calculate the number of digits if a prime is found.
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1281979 * 2^485014 + 1 is prime ... no further hits up to: n = 5,700,000 | |
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rogueVolunteer developer
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Note that the FFT sizes are dependent upon the CPU as not all FFT routines are available on all CPUs.
PRPNet computes the decimal length of primorials and factorials when loaded into the database, so if a prime is found the length on the User Primes page will be the actual decimal length.
But you can use the number of bits to estimate the decimal length. I don't recall if it is the exact number of bits. | |
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BurVolunteer tester
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I recently learned that to estimate whether a calculation fits into L3 cache the FFT size should be multiplied by 8.
Factorial primes are around 450K FFT size now, that'd be 3.6 MB of L3 cache required. Is that really the case? If so, contrary to what I wrote before, multi threading would be recommended on most CPUs. But as far as I know openPFGW doesn't support MT, or does it?
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1281979 * 2^485014 + 1 is prime ... no further hits up to: n = 5,700,000 | |
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But as far as I know openPFGW doesn't support MT, or does it?
No, it does not. /JeppeSN | |
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Michael GoetzVolunteer moderator
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But as far as I know openPFGW doesn't support MT, or does it?
No, it does not. /JeppeSN
Actually, it does -- at least if you use the correct version. But faking things such that PRPNet uses it is non-trivial.
You'll want the 4.x.x release of PFGW to do multithreading. I know others have managed to finagle PRPNet into running LLR multithreaded, but I don't know if anyone did it with PFGW. Search the forums for advice if you want to try it.
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My lucky number is 75898524288+1 | |
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But as far as I know openPFGW doesn't support MT, or does it?
No, it does not. /JeppeSN
Actually, it does -- at least if you use the correct version. But faking things such that PRPNet uses it is non-trivial.
You'll want the 4.x.x release of PFGW to do multithreading. I know others have managed to finagle PRPNet into running LLR multithreaded, but I don't know if anyone did it with PFGW. Search the forums for advice if you want to try it.
You are right! I checked a version 3.8.3 I had. I see now, the version 4 has a -T switch for multithreading. /JeppeSN | |
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I know others have managed to finagle PRPNet into running LLR multithreaded, but I don't know if anyone did it with PFGW. Search the forums for advice if you want to try it.
Confirmed. It also works with pfgw 4.0 or newer in the same way like llr. (Original instructions here)
Instead of changing the "llrexe=" in prpclient.ini, you change the "pfgwexe=" line with the created batch file.
In the batch file, you only write the line:
@pfgw64.exe %* -T4
Change the number in your desired number of cores.
Before, you must update the pfgw.exe file with a newer version (>4.0) than the included version in the prpnet package.
Regards Odi
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BurVolunteer tester
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Thanks, that's much easier than I expected.
FFT is currently at 480K, so modern CPUs won't benefit from multithreading yet. I tested my laptop Ryzen 5 2500U and up to 1500K single-threaded still had the most throughput - I have to admit I'm a bit surprised by that, as it only has 4 MB of L3 cache, so maybe the tests were screwed up by something.
If it was correct, it's way out of the range PRPnet will likely ever reach. But the more I think about it, the less I trust the results. My Ryzen 9 3600X went better with 2 threads at around 640k if I remember correctly.
Hmm, kind of pointless post now, but I leave it here for the record. ;)
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1281979 * 2^485014 + 1 is prime ... no further hits up to: n = 5,700,000 | |
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