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PrimeGrid Challenges 2021

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emoga

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May 13, 2018
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I went ahead and rented a 3090 just to see. Looks like 38 seconds in Linux without any CPU units running.
For reference, my 2080 in Linux averaged 54 seconds over the last 24 hours and a 2080Ti is around 43 seconds.

So the one that beat me could definitely improve its timings if they configured it better. It also ran windows too I suppose.
 
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lane42

Diamond Member
Sep 3, 2000
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Maybe i saw a 3090 under windows vs. a 2080ti under Linux ?
Ill try to find it but don't think i will.
edit, the best i saw was a 2080 super in 54 seconds under windows.
 
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emoga

Member
May 13, 2018
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What's everyone's plans for the rest of the month?

Switching over to try for a MEGA now that most of us have a badge? or going for as many T5K's as possible?

It's a long shot, but I think I'll go GFN17 MEGA's on GPU's and MEGA's on CPUs and hope the math gods hear my prayers.NicePng_praying-png_4354746.png
 
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Ken g6

Programming Moderator, Elite Member
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Dec 11, 1999
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Congrats to @TennesseeTony on finding a prime! :)

Edit: That's weird, I don't see the prime any longer. Was I looking at last year's stats? :confused:

What's everyone's plans for the rest of the month?

Switching over to try for a MEGA now that most of us have a badge? or going for as many T5K's as possible?

It's a long shot, but I think I'll go GFN17 MEGA's on GPU's and MEGA's on CPUs and hope the math gods hear my prayers.View attachment 39362
I'm doing that too. You can calculate your odds of getting a MEGA, for instance. Michael Goetz said in last year's thread that about one in 30,000 tests yields a prime. But he doesn't spread that around because half the people who'd done 30,000 tasks would ask, "why haven't I found a prime yet?!". If you test TPD tests per day, and there are D days to go, the formula is:

1-(29999/30000)^(TPD*D)

So today there are ~20 days to go, and I'm testing about 715 tests per day. As a result I have a 38% chance of finding a MEGA. And falling! I'd better get on with it!!!
 
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Markfw

CPU Moderator, VC&G Moderator, Elite Member
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May 16, 2002
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I should try my new 5950x on the next challenge....
 

StefanR5R

Diamond Member
Dec 10, 2016
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The next team challenge at PrimeGrid will be on March 14 – March 24, 12:00 UTC, at the "Seventeen or Bust" subproject.

This is a CPU-only subproject which is checking very large candidates for primality: Currently, its candidates have 10 million digits. Only the PrimeGrid subprojects GFN-21, GFN-22, and GFN-DYFL ( = GFN-22 at a higher search range) look at larger candidates, and these are GPU subprojects. (OK, GFN-21 also has a CPU application, FWIW.)

I looked up the current search range of Seventeen or Bust and checked its FFT sizes on a Haswell CPU. Haswell and all later Intel CPUs which don't implement AVX-512, and several AMD CPU architectures including Zen 2 and certainly Zen 3, will use the same FFT implementation here, which is "all-complex FMA3 FFT".

SoB-LLR candidatescurrent FMA3 FFT lengthslast-level cache size demand
21181*2^n+1​
2880K … 3M​
22.5 MB … 24 MB​
22699*2^n+1​
2880K … 3M​
22.5 MB … 24 MB​
24737*2^n+1​
2880K … 3M​
22.5 MB … 24 MB​
55459*2^n+1​
3M … 3200K​
24 MB … 25 MB​
67607*2^n+1​
3M … 3200K​
24 MB … 25 MB​

Zen 2 will perform poorly at this, because its level-3 cache is divided into 16 MB segments. (In APUs, it's much less.) Zen 2 will therefore have to perform a lot of main memory accesses and will consequently be unable to keep its FMA units busy.

Zen 3 has got 32 MB level-3 cache segments, one per each compute die. (Zen 3 based APUs will have less.) The Zen 3 CPUs should therefore perform very well in the SoB-LLR subproject, provided that there is exactly one LLR program instance running per each compute die. (That is, one SoB task at a time on 5600X and 5800X, and two tasks at a time on 5900X and 5950X. Thread count per task should be 6 or maybe 12 on 5600X and 5900X, and 8 or maybe 16 on 5900X and 5950X.)

My old 22-core Broadwell-EP CPUs have 55 MB unified L3-cache and will therefore perform OK with 2 simultaneous SoB tasks per socket.
 

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