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Old 2021-02-23, 08:08   #1
drkirkby
 
"David Kirkby"
Jan 2021
Althorne, Essex, UK

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Default PRP tests on known composite numbers

I don’t know what I done wrong while running mprime -m, but I inadvertently succeeded in getting myself about 18 assignments I did not want. They were in the range and type (PRP) tests I wanted, but about a third of them are known to be composite.

https://www.mersenne.org/report_expo...0829939&full=1
https://www.mersenne.org/report_expo...0829407&full=1
https://www.mersenne.org/report_expo...0829473&full=1
https://www.mersenne.org/report_expo...0829521&full=1
https://www.mersenne.org/report_expo...0829669&full=1
https://www.mersenne.org/report_expo...0829717&full=1

Is this a bug, or intensional behaviour?
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Old 2021-02-23, 09:15   #2
LaurV
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Those are PRP-CF and PRP-CF-DC assignments. You are testing if the cofactor (i.e. what remains after the mersenne number is divided by known factors) is (probable) prime or not. If you are not particularly picky about the job you want to do, I suggest to let them run. They will finish very fast in an average computer (pay attention to the exponents, it may be confusing, because they start with 108, but they are 10 times smaller than we test now for primality at the PRP front edge, they are on 10.8M, and not 108M. These ranges were tested 20 years ago, and when you say "they are the range I wanted", you should be aware that there are NO mersenne primes in that range - this question was answered negative 20 years ago).

Last fiddled with by LaurV on 2021-02-23 at 09:17
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Old 2021-02-23, 09:16   #3
kruoli
 
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"Oliver"
Sep 2017
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The exponents you have listed are all of a special work type: PRP-CF. This differs from "normal" PRP such that you will execute a PRP test on the co-factor of a known composite Mersenne number with known factor(s).

Probably, that's not what you wanted, but from our project point of view, this is working as expected. Please make sure your selected work type is not PRP-CF if you do not want to do it. The advantage of PRP-CF is that they will be done quickly and uses less disk space. The disadvantage is: It will not scale as nicely on your high core machine, if you run only one worker.

Edit: Sorry for the crosspost. Somebody else has faster fingers than me.

Last fiddled with by kruoli on 2021-02-23 at 09:17 Reason: Sorry for the crosspost.
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Old 2021-02-23, 11:30   #4
drkirkby
 
"David Kirkby"
Jan 2021
Althorne, Essex, UK

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Smile

Thank you both of you. I see the problem. I'd set my preferences to 160

160 - First time PRP on Mersenne cofactors
instead of the
150 - First time prime tests
which I intended. I must have mis-typed a 6 instead of a 5 - the keys are next to each other!

The assignments at
https://www.mersenne.org/workload/
just indicate PRP, not PRF-CF or PRP-CF-DC . I removed a few characters from this line, as as admin edited some post of mine to remove it, so I have done likewise.
PRP=<AID redacted>,1,2,10829717,-1,99,0,3,1,"86637737,23478826457,1919090830703"
Anyway, if these are not going to take long, and are useful to someone, I will let them run. This computer is running far from optimally at the moment, as it only has two sticks of RAM, not the multiple of 4 it should have.



Dave

Last fiddled with by axn on 2021-02-23 at 13:42 Reason: AID redacted
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Old 2021-02-23, 11:58   #5
kriesel
 
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"Do not post assignment IDs for current assignments, or 64-bit residues for results not yet verified, or MD5 hashes for proof files."
(It's not good to post on a worldwide-readable web site, data that are supposed to be secrets shared only between you, your computer, and the PrimeNet server and perhaps its administrators.) Standard practice is to replace an assignment AID with the text (AID) or (AID redacted); to replace the rightmost two digits of an unverified res64 with __, to replace an MD5 hash with something like the text (hash).

https://www.mersenneforum.org/showpo...64&postcount=2

Worktodo formats https://www.mersenneforum.org/showpo...8&postcount=22

Result formats https://www.mersenneforum.org/showpo...9&postcount=28

A moderator may alter your post to reduce the information leak after the fact.

Last fiddled with by kriesel on 2021-02-23 at 12:06
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Old 2021-02-23, 12:11   #6
firejuggler
 
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Those prp-dc take me about 2H on three core I7-8700, about 3.3to 3.4 GhZ-day
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Old 2021-02-25, 01:21   #7
drkirkby
 
"David Kirkby"
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Quote:
Originally Posted by kruoli View Post

Probably, that's not what you wanted, but from our project point of view, this is working as expected. Please make sure your selected work type is not PRP-CF if you do not want to do it. The advantage of PRP-CF is that they will be done quickly and uses less disk space. The disadvantage is: It will not scale as nicely on your high core machine, if you run only one worker..
Yes, I noticed the cores were not doing much work. I thought they were going to be fairly quick so did not bother setting up more workers. The test was actually using about 40% of the computers resources. I let two finish, but decided to abandon the rest. The CPU in this machine is pretty slow. So the machine does not work too well unless all its cores are in use.

Would more workers, each using less cores, result in more memory access? I really want to avoid that as much as possible at the minute. I'm very aware the memory in my machine is not configured optimally - there are two DIMMs, but they should be installed in groups of 4. Unfortunately, I'm having problems getting hold of the right DIMMs.
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Old 2021-02-25, 10:21   #8
kruoli
 
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"Oliver"
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You should run the throughput benchmark. That will tell you about the optimal settings for your current setup. You could also benchmark different FFT sizes (e.g. one for the PRP wavefront, one for LL-DC wavefront, one for the PRP-CF wavefront) to see what is the most efficient for your machine.

Rule of thumb: The larger the exponent (and by that larger FFT), the fewer workers is optimal. Having a single worker across two physical CPUs is never good, but if I recall correctly, you have only one CPU installed.

If you are unsure about what to do I'd suggest executing the following and reporting the results here (I myself are not sure on how to use 26 cores optimally since this is 2 * 13; the benchmark below will use 24 cores):

Code:
$ ./mprime -m

...

Your choice: 17

Benchmark type (0 = Throughput, 1 = FFT timings, 2 = Trial factoring) (0): 0

FFTs to benchmark
Minimum FFT size (in K) (2048): 512
Maximum FFT size (in K) (8192): 6400
Benchmark with round-off checking enabled (N): N
Benchmark all-complex FFTs (for LLR,PFGW,PRP users) (N): N
Limit FFT sizes (mimic older benchmarking code) (N): N

CPU cores to benchmark
Number of CPU cores (comma separated list of ranges) (26): 24
Benchmark hyperthreading (Y): Y

Throughput benchmark options
Benchmark all FFT implementations to find best one for your machine (N): N
Number of workers (comma separated list of ranges) (1,2,4): 1,2,3,4,6,8,12,24
Time to run each benchmark (in seconds) (15): 30

Accept the answers above? (Y): Y
That will take some time. Make sure that no other processes cause load during that process.

When I ran the above on an eight core machine, the line Number of workers (comma separated list of ranges) (1,2,4): did not show up after I entered that he should test 24 cores since that would be nonsensical for my system. So please make sure that line appears, it will test a lot of combinations on your system.
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