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View Poll Results: Machines I can run 24/7 have
32-bit CPUs or less than 0.75GB per core 4 12.90%
0.75GB memory per core/thread 0 0%
1GB memory per core/thread 15 48.39%
1.5GB memory per core/thread 5 16.13%
2GB memory per core/thread 4 12.90%
More memory than that 3 9.68%
Voters: 31. You may not vote on this poll

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Old 2009-08-18, 14:47   #1
fivemack
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Default How much memory do you have?

You will see attached a list of the numbers mersenneforum has factorised in the last not-quite-two-years.

The sensible thing to do would be to keep attacking the Mersenne numbers from the bottom; 2^863-1 and 2^887-1 are obvious SNFS candidates, 2^899-1 could be either (G185/S271), the time for polynomial selection I think makes it SNFS though G185 would almost certainly get on the Champions list.

I'm wondering whether we might want to leave sense behind and attack 2^941-1. It will take probably six concerted months of sieving by the forces that can be gathered here - a bit less if Dodson joins the fray. But it needs -16e, and that means memory. Hence the poll.
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Old 2009-08-18, 15:00   #2
bsquared
 
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I voted 1.5 GB/core, as everything I have access to has at least that. Most have more.

How about for the LA? You'd probably need a 16GB machine for that, no? There are 8 cpu workstations around here that scoff at 16GB; I'd need special permission to confiscate one for the time needed to do it but I'd be willing to ask if necessary.
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Old 2009-08-18, 15:21   #3
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My machines are running windows XP (32 bit). The largest one (but not running 24/7) has 3 GB available. If 16e is needed, I will be definitely out of the game as I have no machine which has enough memory. (I could run something like Q=10M to 10.1M on the office PC during the christmas holidays if it will still needed then (with the second thread doing prime95 trial factoring or something like this)... )

Quote:
Originally Posted by fivemack View Post
I'm wondering whether we might want to leave sense behind and attack 2^941-1. It will take probably six concerted months of sieving by the forces that can be gathered here - a bit less if Dodson joins the fray. But it needs -16e, and that means memory. Hence the poll.
How much ECM and P+/-1 did this one have? (it might be worth to do P-1 with B1=1e11 and B2=1e16 or 1e17?)

Last fiddled with by Andi47 on 2009-08-18 at 15:24 Reason: repaired smiley (WHY not ;) for a twinkle-smiley?)
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Old 2009-08-18, 15:27   #4
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Good wording on that poll: using units of per core/thread.

This leads to another question: How do core i7 quad-core processors handle 8 threads o' seiving at once?
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Old 2009-08-18, 15:49   #5
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Quote:
Originally Posted by FactorEyes View Post
This leads to another question: How do core i7 quad-core processors handle 8 threads o' seiving at once?
If the machine doesn't have PLENTY of memory, I guess it will be necessary to do less then 8 threads of sieving with 16e and use the other threads for less memory-extensive things.
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Old 2009-08-18, 16:03   #6
Mini-Geek
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My CPU is 64-bit, (and dual-core) it's the OS that's 32-bit. (need a :splittinghairs: smilie) I have a total of 2 GB of memory in this computer, but I also use this computer, so the max memory I'd give it is 1 GB (whether one or two threads). So if it could use 512 MB or less, I could run two threads, otherwise my limit is 1 GB.
Not that my ability to participate should hold too much weight in this...

Last fiddled with by Mini-Geek on 2009-08-18 at 16:05
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Old 2009-08-18, 16:20   #7
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Quote:
Originally Posted by Andi47 View Post
If the machine doesn't have PLENTY of memory, I guess it will be necessary to do less then 8 threads of sieving with 16e and use the other threads for less memory-extensive things.
I'm more worried about how Intel's memory bus handles the I-O to RAM for 8 such memory-intensive processes. I believe fivemack has an i7 920 in his server farm.
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Old 2009-08-18, 16:33   #8
Andi47
 
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Which poly would be used for M941? This one? (parameters are an extrapolation of those I have seen in the mersenneforum for large SNFSes;
skew: I guess 21/6?)

Code:
n: 2468815427808777830385945175570959888649322954010151512577652841207233127175594988619285951813249353482864131674513502872982111245757912252275917421142241044267118542381889815949472721865947896251559297022100274282885756253947868389157090816092206938192397903861973556952725044519
c6: 1
c0: -2
Y0: 182687704666362864775460604089535377456991567872
Y1: 1
skew: 1.12
rlim: 200000000
alim: 200000000
lpbr: 32
lpba: 32
mfbr: 64
mfba: 64
rlambda: 2.6
alambda: 2.6
Edit: Sieving with this poly from Q=70M to Q=70,000,200 with 16e takes 792 MB RAM and ~1.65 GB virtual memory (disk space).

Code:
total yield: 44, q=70000213 (7.73545 sec/rel)
(hyperthreaded P4 @ 3.4 GHz, windows XP, second thread busy with yafu)

Last fiddled with by Andi47 on 2009-08-18 at 16:50 Reason: benchmark
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Old 2009-08-18, 17:13   #9
fivemack
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On previous large, but not 16e, NFS sieving jobs, I've found that running eight jobs, each assigned with taskset to one thread of the i7/920, gives about 40% more throughput than running four jobs each assigned to one core of the i7/920 with the other threads unloaded.

(IE it can be a 4 x 2.8GHz machine or effectively an 8 x 2GHz machine)

I think I've done the measurements to show that 2^941-1 is still a 32/32 problem, meaning the matrix shouldn't be worse than 30M on a side and will be happy on the i7 that I have already. The sieving's the hard part. I need to figure out whether 200M is the right limit, and for a job this big I ought to get round to doing the analysis of duplication rates to see if it's better to do one side or both.

On a 2.66GHz Core2Duo that I have lying around here, running

Code:
./batalov-lasieve/gnfs-lasieve4I16e -a M941.poly -f 70000000 -c 200
top says
Code:
22952 twomack   25   0  978m 456m  504 R  100 22.9   1:32.15 gnfs-lasieve4I1
and the output is a reassuringly consistent

Code:
total yield: 44, q=70000213 (1.65068 sec/rel)
(there is one useful prime in that range, 0x42c1de7 = 70000103, above which are precisely two ideals)

Last fiddled with by fivemack on 2009-08-18 at 17:14
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Old 2009-08-18, 17:20   #10
Mini-Geek
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How much harder would it be to break the SNFS record (M1039) than M941? Candidates might be M1051 (22-bit factor known, 1030-bit cofactor) or M1061 (no factors known).

Last fiddled with by Mini-Geek on 2009-08-18 at 17:28
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Old 2009-08-18, 17:38   #11
jasonp
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for 1000+ bit numbers you'd need large primes > 32 bits, which msieve cannot currently handle. You would also need > 2^32 relations, which msieve also cannot currently handle (though that's easier to fix).
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