Unfixing FFT length for LL test

[tichy]

Hello,

some time ago I started an LL test on an exponent which apparently falls into some boundary region, because at the start of the test mprime (25.11) first checked if the 2560K FFt length is sufficient wrt calculation errors. Later in the worktodo file it appeared with a fixed FFT length attached.

Then I switched to mprime 26.4. I used the same worktodo entry and checkpoint left by the 25.11 version. However, now I've noticed that it takes mprime 26.4 less time per iteration with a slightly larger exponent for which it has selected 2688K FFT length, e.g.:

[Worker #1 Jan 12 21:08] Resuming primality test of M50493523 using Core2 type-3 FFT length 2688K, Pass1=896, Pass2=3K, 7 threads
[Worker #2 Jan 12 21:08] Resuming primality test of M49044143 using Core2 type-3 FFT length 2560K, Pass1=640, Pass2=4K, 7 threads
[Worker #2 Jan 12 21:13] Iteration: 19380000 / 49044143 [39.51%].  Per iteration time: 0.022 sec.
[Worker #1 Jan 12 21:15] Iteration: 17090000 / 50493523 [33.84%].  Per iteration time: 0.019 sec.

So I'm considering removing the 2560K FFT length fix and verifying both the new selected FFT length and iteration timing for that exponent, however, I'd like to make sure I won't break anything (e.g. internal checkpoint file structure is independent of the FFT length).

Thank you in advance,

[Prime95]

You can safely delete the "FFT2=" string from worktodo.txt. The save files are compatible.

[tichy]

Thank you. Mprime again tried 2560K FFT, so this time I enforced 2688K length - and to my surprise it seems to works faster:

[Worker #1 Jan 13 00:02] Iteration: 19850000 / 49044143 [40.47%].  Per  iteration time: 0.020 sec.
[Worker #2 Jan 13 00:02] Iteration: 17590000 / 50493523 [34.83%].  Per  iteration time: 0.022 sec.
[Worker #1 Jan 13 00:05] Iteration: 19860000 / 49044143 [40.49%].  Per  iteration time: 0.019 sec.
[Worker #2 Jan 13 00:05] Iteration: 17600000 / 50493523 [34.85%].  Per  iteration time: 0.020 sec.
[Worker #1 Jan 13 00:08] Iteration: 19870000 / 49044143 [40.51%].  Per  iteration time: 0.019 sec.
[Worker #2 Jan 13 00:08] Iteration: 17610000 / 50493523 [34.87%].  Per  iteration time: 0.020 sec.
[Worker #1 Jan 13 00:11] Iteration: 19880000 / 49044143 [40.53%].  Per  iteration time: 0.019 sec.
[Worker #2 Jan 13 00:12] Iteration: 17620000 / 50493523 [34.89%].  Per  iteration time: 0.020 sec.
[Worker #1 Jan 13 00:14] Iteration: 19890000 / 49044143 [40.55%].  Per  iteration time: 0.019 sec.
[Worker #2 Jan 13 00:15] Iteration: 17630000 / 50493523 [34.91%].  Per  iteration time: 0.020 sec.