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Old 2022-09-11, 17:52   #100
Magellan3s
 
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I'm pretty uninformed when it comes to this but.....

Is there a reason mfaktc can't be used? I know it has a minimum exponent size requirement but can that be changed?

Last fiddled with by Magellan3s on 2022-09-11 at 17:52
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Old 2022-09-11, 18:22   #101
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Mfaktc is great at finding small factors but the miminal possible factor size of M1277 is many many orders of magnitude larger than anything it can find. We know this because of the amount of ECM completed on this number.

Last fiddled with by bsquared on 2022-09-11 at 18:25 Reason: Forgot the M
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Old 2022-09-11, 18:38   #102
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Quote:
Originally Posted by bsquared View Post
Mfaktc is great at finding small factors but the miminal possible factor size of M1277 is many many orders of magnitude larger than anything it can find. We know this because of the amount of ECM completed on this number.
I think I understand, thank you!
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Old 2022-09-11, 18:51   #103
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Aside from the low-exponent issue, there's a limit in mfaktc at 95 bits, mfakto at 92 bits. M1277 has already been TF to 68 bits, and it took ~47,000 GHD. To go to 69 bits would take another ~47,000 GHD, which is ~3 weeks on an RTX2080 GPU. From 69-70 would take twice as long, 70-71 four times, etc., growing exponentially. Well before ~227 times 3 weeks, run time gets prohibitively long. And if not for that, from 95 bits to 1277/2 is beyond its current capability, requiring someone to code new kernels. https://www.mersenne.ca/exponent/1277
There's no multi-GPU implementation of TF for Mersenne numbers, so running a span of x to x+y bits, only parallelizes to 2 GPUs:
x to x+y-1 on GPU a, x+y-1 to x+y on GPU b, giving about equal run time for same model GPUs.
Some other possibilities were mentioned earlier in this thread https://mersenneforum.org/showpost.p...3&postcount=18
and VBCurtis responds that reachable TF is pointless because of the amount of ECM that has been done
https://mersenneforum.org/showpost.p...7&postcount=19
My attempted summary of factoring choices & past M1277 effort is https://mersenneforum.org/showpost.p...5&postcount=22 which indicates that almost any factors <166. bits would have already been found by ECM, so there's nothing reachable by TF remaining.
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Old 2022-09-11, 19:09   #104
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Quote:
Originally Posted by kriesel View Post
Aside from the low-exponent issue, there's a limit in mfaktc at 95 bits, mfakto at 92 bits. M1277 has already been TF to 68 bits, and it took ~47,000 GHD. To go to 69 bits would take another ~47,000 GHD, which is ~3 weeks on an RTX2080 GPU. From 69-70 would take twice as long, 70-71 four times, etc., growing exponentially. Well before ~227 times 3 weeks, run time gets prohibitively long. And if not for that, from 95 bits to 1277/2 is beyond its current capability, requiring someone to code new kernels. https://www.mersenne.ca/exponent/1277
There's no multi-GPU implementation of TF for Mersenne numbers, so running a span of x to x+y bits, only parallelizes to 2 GPUs:
x to x+y-1 on GPU a, x+y-1 to x+y on GPU b, giving about equal run time for same model GPUs.
Some other possibilities were mentioned earlier in this thread https://mersenneforum.org/showpost.p...3&postcount=18
and VBCurtis responds that reachable TF is pointless because of the amount of ECM that has been done
https://mersenneforum.org/showpost.p...7&postcount=19
My attempted summary of factoring choices & past M1277 effort is https://mersenneforum.org/showpost.p...5&postcount=22 which indicates that almost any factors <166. bits would have already been found by ECM, so there's nothing reachable by TF remaining.
This cleared things up even more, thank you!
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Old 2022-09-12, 09:15   #105
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Quote:
Originally Posted by kriesel View Post
There's no multi-GPU implementation of TF for Mersenne numbers, so running a span of x to x+y bits, only parallelizes to 2 GPUs
Not my intention to contradict anything you (and other guys) said about the difficulty of such job, just want to point out that the TF can be easily paralelized to 960 GPUs (for the 4620 classes version) just by rewriting the checkpoint file of mfaktc, for example. Of course, writing a "parallel" version (where you can specify the class) is quite easy. However, this is futile, it will just shorter the time from (arbitrary) 900 million years to one million years
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Old 2022-09-12, 12:12   #106
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Quote:
Originally Posted by LaurV View Post
TF can be easily paralelized to 960 GPUs (for the 4620 classes version) just by rewriting the checkpoint file of mfaktc, for example. Of course, writing a "parallel" version (where you can specify the class) is quite easy. However, this is futile, it will just shorter the time from (arbitrary) 900 million years to one million years
And require setting up a foundation (def'n 3b) to maintain the 1000 GPU farm including a few dozen hot spares for the long term. For NO factor-found utility, since ECM has already covered any reachable bit level. Ernst's Mfactor could be used in an analogous futile mass space heater game using CPUs, using existing code, and achieving even larger absurd run time estimates. And it allows specifying start and end k values, so each of the many classes could be subdivided for greater futile parallelism.

Last fiddled with by kriesel on 2022-09-12 at 13:04 Reason: apparently razzes are now required for certain posts. Some mods have no sense of humor, or misperceive that in others, or ?
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Old 2022-09-12, 12:20   #107
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Quote:
Originally Posted by kriesel View Post
And require setting up a foundation to maintain the 1000 GPU farm including a few dozen hot spares for the long term. For NO factor-found utility, since ECM has already covered any reachable bit level. Mfactor could be used in an analogous futile mass space heater game using CPUs, using existing code, and achieving even larger absurd run time estimates. And allows specifying start and end k values, so each of the many classes could be subdivided for greater futile parallelism.
Yeah, you are 100% correct.

Instead we should be TFing RSA-1024 (and ECMing also). It's smaller so it should be really easy.

I think you missed the trailing razz emoji in your quote. I put another one in here, I hope you don't miss that one also.
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