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Message boards : Proth Prime Search : Smaller FFT size, longer CPU time

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Bur
Volunteer tester

Joined: 25 Feb 20
Posts: 332
ID: 1241833
Credit: 22,611,276
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Message 145337 - Posted: 18 Nov 2020 | 18:28:53 UTC
Last modified: 18 Nov 2020 | 18:30:51 UTC

While browsing PPS Mega tasks, I saw that some took 4100 s, some 5400 s. I assumed the latter had the larger FFT size and larger k, but not so.

The 4100 s tasks had FFT = 256k, the 5400 s ones had FFT = 240k.

Here are examples of each: 4100 s and 5400 s or the whole list here.

The difference seems to be the pass1 and pass2, in one case pass1 is larger, in the other pass2 is larger. And a is either 3 or 5.

What do these parameters mean and how do they influence the CPU time in such a way that smaller FFT size means longer CPU time? Especially since the tasks with shorter run times had the larger k and accordingly larger FFT.
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Primes: 1281979 & 12+8+1979 & 1+2+8+1+9+7+9 & 1^2+2^2+8^2+1^2+9^2+7^2+9^2 & 12*8+19*79 & 12^8-1979 & 1281979 + 4 (cousin prime)

Eudy Silva

Joined: 26 Aug 17
Posts: 1325
ID: 918937
Credit: 221,903,924
RAC: 9,090

Message 145348 - Posted: 18 Nov 2020 | 20:25:28 UTC - in response to Message 145337.

There was some talking about this last year:
https://www.primegrid.com/forum_thread.php?id=8628&nowrap=true
____________
"Accidit in puncto, quod non contingit in anno."
Something that does not occur in a year may, perchance, happen in a moment.

Bur
Volunteer tester

Joined: 25 Feb 20
Posts: 332
ID: 1241833
Credit: 22,611,276
RAC: 4,081

Message 145388 - Posted: 19 Nov 2020 | 17:34:11 UTC - in response to Message 145348.

Ok, thanks I will continue in that thread.
____________
Primes: 1281979 & 12+8+1979 & 1+2+8+1+9+7+9 & 1^2+2^2+8^2+1^2+9^2+7^2+9^2 & 12*8+19*79 & 12^8-1979 & 1281979 + 4 (cousin prime)

Message boards : Proth Prime Search : Smaller FFT size, longer CPU time

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