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Old 2021-07-11, 03:46   #18
Romulan Interpreter
LaurV's Avatar
Jun 2011

24×13×47 Posts

I work around this (for years by now) by making poly selection in less cores. What I witnessed is the fact that when many cores are used, like 10, 12, 16, or 18, then there are EVERY time 2 or 3 cores that are "lazier". While the rest of the cores finish their job in the promised amount of time, the lazier cores will take a lot more, sometimes more than double, and the main problem is that there is NO WAY (known to me) to resume or to interrupt without losing the whole job. Sometimes you can see (from the temporary files remaining in the folder, because yafu will clean the files for the cores that finished the work) which cores remained and you can stop with ctrl+c, and you restart, and if lucky (enough polys in the file, or whatever) yafu will move to sieving. But this is extremely risky business, if it doesn't move to sieving it will start from scratch.

So, my "plan B" is to run the poly selection in 4 or 6 cores - it will take proportionally longer, but I have the other cores free to do other jobs, or to search polys for more composites in the same time, if I have enough of them collected (different yafu copies in different folders). When less cores are used, they will all finish in the promised amount of time, with a higher probability, or there can be one core taking a bit longer, but I can avoid the situation where most of the cores sit idle for one day or longer.

When I am really in hurry, I will ask Max to get a poly for me, which he did repeatedly, or I will ask on the public forum, but this method doesn't always work. For example, last adventure was getting a poly for aliq_814848 i2066 C156, which pissed me off sooo much. It took yafu longer than 2 days (it says in factor log that needs 60000 seconds in 18 cores, which is about 16 hours) with three different trials, and I still didn't get any useful poly, because during the monsoon season in Thai, we have rain and thunderstorms and electricity breaks every day, and I had to repeatedly restart. So I asked Max and he provided me a poly in an hour or so, and I wondered wadahak server he has there with a million cores, to which he replied that "it took cado 30 minutes to generate, in 4 cores". He almost made me install cado, except I seem to be too stupid and have too less time to be able to handle anything else except yafu (win7 OS here, still). I still dream to be able to run msieve version which can generate polys using the GPU, as my CPU resources are very scarce in comparison, but never found the time to go through the initial setup process (compile? install? learning curve? what?). But anyhow, Max's poly didn't sieve right either, so I just decided this C156 is cursed, and didn't bother him again, I just searched for another poly "normal way", in 6 cores, in a smaller computer with a UPS (I do not have such a large UPS to keep alive the big machines, such toys are bloody expensive), which took three days (and guess what? the freaking electricity didn't break even once, in the three days involved!), and now the C156 is in sieving in the 18-cores machine (about 16M relations from the 44M needed, about two days to go).

That was just an example. A possibility to resume poly selection, or to just stop it and tell yafu "I am done with you, just select the best poly from what you already filed up to now, and move to sieving" (assuming you, the user, know what you are doing), should worth millions in this corner of the flat earth But I know your time is limited too.

Edit: Just for clarity, I am still using this, as it is by far the fastest in my machines, from what I tried. I didn't, however, tried "most newest" versions. So, if my "problem" is already solved, please enlighten me.
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Last fiddled with by LaurV on 2021-07-11 at 04:43
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