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2021-06-28, 02:06   #320
Chuck

May 2011
Orange Park, FL

3×13×23 Posts

Quote:
 Originally Posted by ATH I guess this could not be an mprime issue? Just in case could someone with a Prime95 (Windows) AVX-512 computer test one of these? No need to finish it unless you want to, just run like 50% of stage1 to check if you get a roundoff error: Pplus1=N/A,1,2,4037479,-1,2500000,250000000,2,70 Pplus1=N/A,1,2,4040059,-1,2500000,250000000,2,70
I'll try these two.

 2021-06-28, 02:32 #321 Chuck     May 2011 Orange Park, FL 3·13·23 Posts I didn't get any roundoff errors. Attached Thumbnails
 2021-06-28, 04:21 #322 Citrix     Jun 2003 2·7·113 Posts If doing P-1 work on (k^p-1)/(k-1) or (k^p+1)/(k+1) with p prime Does Prime95 automatically includes p in the B1 stage? Thanks
2021-06-28, 05:47   #323
ATH
Einyen

Dec 2003
Denmark

2×7×227 Posts

Quote:
 Originally Posted by Chuck I didn't get any roundoff errors.
@Prime95: Is this strange that there are no roundoff errors in Prime95 on AVX-512 200K on these 2 exponents that I got roundoff errors on in mprime? or is it very dependent on the specific processor?

Last fiddled with by ATH on 2021-06-28 at 05:47

2021-06-28, 07:18   #324
Prime95
P90 years forever!

Aug 2002
Yeehaw, FL

7×1,091 Posts

Quote:
 Originally Posted by Citrix If doing P-1 work on (k^p-1)/(k-1) or (k^p+1)/(k+1) with p prime Does Prime95 automatically includes p in the B1 stage?
I believe so. Can you run a small test case?

2021-06-28, 07:19   #325
Prime95
P90 years forever!

Aug 2002
Yeehaw, FL

1DD516 Posts

Quote:
 Originally Posted by ATH @Prime95: Is this strange that there are no roundoff errors in Prime95 on AVX-512 200K on these 2 exponents that I got roundoff errors on in mprime? or is it very dependent on the specific processor?
One started at 2/7, the other started at 6/5.

2021-06-28, 17:37   #326
ATH
Einyen

Dec 2003
Denmark

2×7×227 Posts

Quote:
 Originally Posted by Prime95 One started at 2/7, the other started at 6/5.
Yeah I switched it :( In case whoever tested it wanted to finish it, then it would not be wasted effort.

Quote:
 Originally Posted by Prime95 Other AVX-512 FFT maximum exponents that remain to be tested (turn on roundoff checking): Code: 22469 33423
I'm working on these 2 and going upwards after them. I'm doing P+1, do I need to do P-1 as well on each exponent?
Should I continue above the maximum in case of no failures below?

Edit: I reached a failure in the 33423 case. I started at M32611 and reached a roundoff error at M33391, should I do more testing for this FFT?

Code:
[Work thread Jun 28 16:01:03] P+1 on M33391, start=2/7, B1=100000000, B2=10000000000
[Work thread Jun 28 16:01:03] Using AVX-512 FFT length 1536
[Work thread Jun 28 16:09:30] Possible roundoff error (0.4520854), backtracking to last save file.
[Work thread Jun 28 16:09:30] Using AVX-512 FFT length 1536
[Work thread Jun 28 16:17:55] Possible roundoff error (0.4520854), backtracking to last save file.
[Work thread Jun 28 16:17:55] Using AVX-512 FFT length 1536
[Work thread Jun 28 16:26:17] Possible roundoff error (0.4520854), backtracking to last save file.
Max roundoff errors before the failure:
M33301 Round off: 0.4065263058
M33347 Round off: 0.4113334932
M33353 Round off: 0.4064540519
M33359 Round off: 0.401012083
M33377 Round off: 0.4146345477

Last fiddled with by ATH on 2021-06-28 at 18:06

2021-06-28, 19:49   #327
R. Gerbicz

"Robert Gerbicz"
Oct 2005
Hungary

2×32×83 Posts

Quote:
 Originally Posted by ATH Yeah I switched it :( In case whoever tested it wanted to finish it, then it would not be wasted effort. ... I'm doing P+1, do I need to do P-1 as well on each exponent? Should I continue above the maximum in case of no failures below? Edit: I reached a failure in the 33423 case. I started at M32611 and reached a roundoff error at M33391, should I do more testing for this FFT? Code: [Work thread Jun 28 16:01:03] P+1 on M33391, start=2/7, B1=100000000, B2=10000000000 [Work thread Jun 28 16:01:03] Using AVX-512 FFT length 1536 [Work thread Jun 28 16:09:30] Possible roundoff error (0.4520854), backtracking to last save file. [Work thread Jun 28 16:09:30] Using AVX-512 FFT length 1536 [Work thread Jun 28 16:17:55] Possible roundoff error (0.4520854), backtracking to last save file. [Work thread Jun 28 16:17:55] Using AVX-512 FFT length 1536 [Work thread Jun 28 16:26:17] Possible roundoff error (0.4520854), backtracking to last save file. Max roundoff errors before the failure: M33301 Round off: 0.4065263058 M33347 Round off: 0.4113334932 M33353 Round off: 0.4064540519 M33359 Round off: 0.401012083 M33377 Round off: 0.4146345477
For example on M33391 we know a pretty large d (=p1*p2*p3*p4) divisor which enables a good error checking at least on the first stage of P+-1 : do the computation also in Z[d] and then regularly do the check for the intermediate number(s) that r(i) mod d is still good. What could give you a greedy FFT size.

Or for example at P-1 test the check is only: we computed that b^e==res mod N then check: res==b^(e mod eulerphi(d)) mod d [Euler-Fermat], for gcd(b,d)=1 and d|N, so you need to update only the e mod eulerphi(d) at each step and not the slightly more costly b^e mod d. [since d is usually very small compared to N this makes not a large difference in timing].

Last fiddled with by R. Gerbicz on 2021-06-28 at 19:52 Reason: typo, corrections

2021-06-28, 20:13   #328
Prime95
P90 years forever!

Aug 2002
Yeehaw, FL

7×1,091 Posts

Quote:
 Originally Posted by ATH I'm doing P+1, do I need to do P-1 as well on each exponent? Should I continue above the maximum in case of no failures below?
P+1 is sufficient. Don't go above the maximum if no failures are found.

Quote:
 I started at M32611 and reached a roundoff error at M33391, should I do more testing for this FFT?
To be safe, length 1.5K AVX-512 FFT max exponent changed to 33380.

 2021-07-14, 23:46 #329 Viliam Furik     "Viliam Furík" Jul 2018 Martin, Slovakia 2·11·31 Posts I am having a worker-count related issue with Prime95. I have been using (4 workers, 3 cores) configuration for a while. Now I've decided to make it (12 workers, 1 core), because of the better throughput at 50K FFT, which is what I am doing now - P-1 in 1M range on factored exponents. So I went and set the Prime95 accordingly. When I started the workers, it went fine, but when it got to starting worker #6, it crashed. The same happened when I restarted the program. Workers #1 to #4 have plenty of work in their worktodo entries, worker #5 was assigned CERT, but the rest is hungry. Is it possible that it crashes because of that? I am using version 30.6b4, processor is Ryzen 9 3900X (12 cores). After a few testing attempts, it seems to crash precisely when all the first 4 workers finally agreed on RAM consumption (3 of them are in stage 2) and started working. That happens somewhere around the start of worker #8, i.e. about 40 seconds after the start of the program (there are 5-second delays between worker starts).
 2021-07-15, 01:30 #330 Viliam Furik     "Viliam Furík" Jul 2018 Martin, Slovakia 12528 Posts Weird... When I fed the workers with assignments, it's no longer crashing. But I am going to (6 workers, 2 cores), because 12 workers make the CPU really hot, 92 °C.

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