How much is a prime factor worth?

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Registriert: 12.11.2014 09:26

How much is a prime factor worth?

#1 Ungelesener Beitrag von Dunckx » 01.04.2019 16:21

I have now run Yoyo@home for five years on the same pc and I thought it might be interesting to work out the "cost" of finding prime factors, since one of the reasons I picked this project was the comments I had read by mathematicians who highlighted the vast expenditure of CPU clock cycles on the problem. I recall that one stated that more CPU cycles have been used finding factors than in all of the CGI effects in all the movies ever made.

Interestingly, CPU use and CPU power drain are non-linearly related:

100% CPU use = 62W
75% CPU use = 60W
25% CPU use = 35W
12% CPU use = 22W
0% CPU use = 7W (!)

Sadly, I didn't manage to rig things for 50% use, but I suspect that it is not much less than 60W. It's a four core CPU with hyperthreading and running it with HT doesn't use much more electricity than running without HT. These numbers were obtained by running the ECM subproject only with a varying number of work units. Percent CPU use was monitored by Windows Task Manager and the CPU power draw by Core Temp. My CPU is an i7 4770S at 3,9GHz.

By using my electricity "smart meter" and turning BOINC off for a week, I discover that the difference in power consumption is about 1,6kWh per day, and this must be equal to the difference in CPU power consumption plus the difference for the rest of the system, mostly VRM. To consume 1,6kWh per day corresponds to 67W continuous load.

So, my pc consumes 67W including the differential for VRM, chipset and memory, over and above what it consumes for my normal use scenario. 2016 was a leap year so there are five 365 day years plus one day to account for, yes, a totally unjustifiable degree of precision, but never mind. My electricity price is about 20c per kWh.

20c per kWh x 0,067 x 24 x (5 x 365 +1) = €590 total for 3MWh to two significant figures, spread over five years.

The figure for the ECM subproject is less than this because I also crunched for Muon. Let's split it according to the subproject credits. This is not as simple as it should be. I commented some time ago on the fact that the subproject totals do not add up!

Muon 2001517
ECM 21627226
Evolution 2035
Odd Weird 1747
Crunch 1005
Total 23633530

BUT my total score according to the stats is 23888617. There is a discrepancy of 23888617-23633530 = 255087 too many and this is too big to be accounted for by credits in the pipeline. What to do? Let's just assume that we are dealing with Muon and ECM only and round the subproject numbers, ignoring the stats total. Obviously this is wrong, but I don't see a practical alternative. An error of 250k in 24M is only 1%, but it's irritating that in such a mathematics-intensive project, the credit numbers don't add up. Yes, I'm complaining at having too many ;-)

Muon 2.000.000
ECM 21.600.000

So ECM is 21,6/23,6 = 91,5% of 587,24 = 537,5 / 4 = 134 so let's call it €135 per prime factor, or 0,75MWh each.

Hope it was worth it! The bare minimum for these four factors is €540, 3MWh!


As a final note, the energy expenditure and carbon footprint are not anything like 100% wasted. This pc sits in my living room and consequently serves as an "intelligent room heater", reducing the cost of running the central heating during the colder part of the year by 2,5kWh (guessed) per day when it is running BOINC, which is a significant contribution. I don't have air conditioning, so this is not counterbalanced by a cooling bill for the warmer months. Perhaps intelligent room heaters are a way forward in reducing environmental impact. Ordinary heaters only convert fuel to heat, computers produce data as a useful byproduct ;-)

It'd be interesting to see cost comparisons from other users based on their own CPU and subproject credit breakdowns. I think these figures above are actually towards the top end of the spread, as, looking at my position in the ECM subproject, most participants around me have considerably more factors for the credit numbers and therefore the mean cost per factor for the subproject overall is likely to be less than for my system.

Happy crunching!

Beiträge: 22
Registriert: 15.07.2016 00:53

Re: How much is a prime factor worth?

#2 Ungelesener Beitrag von mister.marmot » 04.04.2019 10:36

I control power usage by downclocking and/or downvolting the CPU and keep CPU usage pegged at 100%
The computers heat the house so all the costs of calculations are essentially zero as I would have had to use a dumb heater to keep the house heated.

Of course, the machines are shutdown as the summer months come as the electric company will charge peak hour costs and it would be anti-climate to use a/c to cool the machines.
Perhaps intelligent room heaters are a way forward in reducing environmental impact. Ordinary heaters only convert fuel to heat, computers produce data as a useful byproduct

Yes, these should take on more of an allure. I heard a BBC story about a Siberian woman using her BtC equipment for income and heating all through their cold winters.

BTW, your 20 cents/kWH is almost double what we pay here.


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