Mersenne Rig (take 2)

simon389 · 2014-11-28, 04:16

Hi Mersenners,

About 14 months ago I was in discussion here about getting back into crunching Mersenne primes for the first time since 2001. You can read the old thread here:

http://www.mersenneforum.org/showthread.php?t=18521

Unfortunately, I had some life delays that I won't go into (major health issue) that sort of caused a bunch of havoc. But now I'm back and excited again to build a machine.

The good news is my budget has increased for this project. Can somebody walk me through the best use to spend $1000 on a headless Mersenne cruncher setup? What is the ideal CPU/graphics/RAM? I am ok with buying used equipment if it means more crunches/hour for my budget. I can overclock if you feel it would benefit the situation, however I'm trying to keep the rig somewhat quiet since it'll sit at my feet at my office.

Prime95 suggested this:

Quote:

IMO, invest your money in:
a) a K series non-hyperthreaded CPU for overclocking
b) fast RAM, DDR3-2400 or better
c) an efficient power supply, the extra upfront cost should pay for itself in lower electric bills.

IMO, do not invest your money in:
a) motherboard - choose the cheapest board from a reputable maker
b) quantity of RAM
c) disk, case, etc.

Is this still ideal?

TheMawn · 2014-11-28, 04:34

Yes. If you're going modern, the i5-4670K is your best bet. You're not spending the extra $100 on extra threads that serve no purpose. The same applies to older generations. Get the i5-XXXXK.

Get faster memory, not higher capacity memory. I'm currently using 125MB on two LL's and two DC's. 32 GB would serve no purpose.

The more efficient power supplies are more important if you're going to run a heavy GPU as well. Where the CPU might draw at most 60W-80W, a GPU can pull 150W-300W depending on what you get.

A PSU that is 80% efficient and requiring 100W draws 125W at the wall. The 25W loss equates to 1 kWh after 40 hours which comes to between 4 and 5 kWh per week, anywhere from $0.50 to $0.75 per week. That's $25 - $40 per year.

A PSU that is 85% efficient requiring 100W draws only 117.6W at the wall, but the 7.4W difference could be $7 - $10 per year. If your system requires 300W instead, triple that amount.

The motherboard need only be powerful enough to support your hardware. I can vouch for ASUS boards being able to give a CPU enough of an overclock to keep 2400 MHz memory bottlenecked. If overclocking, you want to make sure the motherboard is capable of supplying that much power to the CPU, and most boards probably can.

I'll leave the discussion of the "best" GPU to buy to someone else. Used hardware isn't my area of expertise but I know it's the best place to go.

Dubslow · 2014-11-28, 15:31

It might be worth waiting for Broadwell in a few months, or longer for DDR4 memory.

fivemack · 2014-11-28, 16:14

I'm not expecting Broadwell to be excitingly much faster, except conceivably on the models with L4 cache. The better Broadwell multiplier might be good for TF, but if you are doing TF on CPUs you have already left the path of wisdom.

For current hardware details I would agree with TheMawn, and would say either to buy now or to wait a year or so for the Sky Lake/K models with 512-bit-wide AVX and large L4 cache to exist and for George to get the Prime95 code to work well on them.

axn · 2014-11-28, 16:55

If it fits within budget, go for a 5820K

http://ark.intel.com/compare/80811,75048,82932

EDIT:- For GPU (TF only), I think 970 is the best one.

fivemack · 2014-11-28, 17:31

Given the price of DDR4 memory, the price of X99 motherboards, and the need for a GPU, I haven't found a 5820K system which is cheaper than two i5-4670K systems.

henryzz · 2014-11-28, 22:04

Quote:

Originally Posted by fivemack

Given the price of DDR4 memory, the price of X99 motherboards, and the need for a GPU, I haven't found a 5820K system which is cheaper than two i5-4670K systems.

I would imagine quite a bit less power usage though.

Mark Rose · 2014-11-28, 23:13

Quote:

Originally Posted by henryzz

I would imagine quite a bit less power usage though.

Maybe not. At idle, my Haswell system with no GPUs draws 30 watts. The 4790k draws 88 watts at design power, while the 5820k draws 140. At first that looks like 170 watts vs 236 watts. But the two 4790k's give you 8 cores versus the 6 cores of the 5820k, and both consume roughly the same amount on a per-core basis (42.5 vs 44.3). But the 4790k cores are 21% faster at stock clocks for only 4% more power.

VBCurtis · 2014-11-29, 05:46

Quote:

Originally Posted by Mark Rose

Maybe not. At idle, my Haswell system with no GPUs draws 30 watts. The 4790k draws 88 watts at design power, while the 5820k draws 140. At first that looks like 170 watts vs 236 watts. But the two 4790k's give you 8 cores versus the 6 cores of the 5820k, and both consume roughly the same amount on a per-core basis (42.5 vs 44.3). But the 4790k cores are 21% faster at stock clocks for only 4% more power.

And, as Tom mentioned, the 5820 has no GPU built-in. I think the 5820 only holds its own on tasks where HT is fruitful- e.g. NFS sieving. For pure prime-searching, an i5 is surely the way to go.

TheMawn · 2014-11-29, 16:01

I've ordered parts for a Haswell-E system. I sprung for the i7-5930K, as I will likely be adding stuff to it until it is ready to take over as my main computer. I worked a bunch of overtime at my temporary job during fall so anything above a "bare-bones" system is a treat to myself.

As a pure-LL machine, there is absolutely no reason to go for Haswell-E. The only real edge Haswell-E has over Haswell is the memory bandwidth. Where my i5-3570k (admittedly this is only Ivy Bridge) is bottlenecked by 2400 MHz memory around the 4.0 GHz mark, the increased memory bandwidth will likely be able to properly feed six cores at maybe even an increased frequency.

On the other hand, Haswell-E gives you the option to run many GPU's without completely crippling yourself in any applications where you actually need the PCI-E lanes. This is part of my reasoning for spending the extra $200. Even 3 GPU's at x8/x8/x8 only leaves 4 lanes open for whatever PCI-E based devices remain. 40 lanes is certainly overkill, but I'm all for that.

xilman · 2014-11-30, 20:16

Quote:

Originally Posted by TheMawn

I40 lanes is certainly overkill, but I'm all for that.

You can never have too much overkill

2014-11-28, 16:55	#5
axn Jun 2003 3²·5·113 Posts	If it fits within budget, go for a 5820K http://ark.intel.com/compare/80811,75048,82932 EDIT:- For GPU (TF only), I think 970 is the best one. Last fiddled with by axn on 2014-11-28 at 16:57

2014-11-29, 16:01	#10
TheMawn May 2013 East. Always East. 11·157 Posts	I've ordered parts for a Haswell-E system. I sprung for the i7-5930K, as I will likely be adding stuff to it until it is ready to take over as my main computer. I worked a bunch of overtime at my temporary job during fall so anything above a "bare-bones" system is a treat to myself. As a pure-LL machine, there is absolutely no reason to go for Haswell-E. The only real edge Haswell-E has over Haswell is the memory bandwidth. Where my i5-3570k (admittedly this is only Ivy Bridge) is bottlenecked by 2400 MHz memory around the 4.0 GHz mark, the increased memory bandwidth will likely be able to properly feed six cores at maybe even an increased frequency. On the other hand, Haswell-E gives you the option to run many GPU's without completely crippling yourself in any applications where you actually need the PCI-E lanes. This is part of my reasoning for spending the extra $200. Even 3 GPU's at x8/x8/x8 only leaves 4 lanes open for whatever PCI-E based devices remain. 40 lanes is certainly overkill, but I'm all for that. Last fiddled with by TheMawn on 2014-11-29 at 16:02

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2014-11-28, 04:34	#2
TheMawn May 2013 East. Always East. 6BF₁₆ Posts	Yes. If you're going modern, the i5-4670K is your best bet. You're not spending the extra $100 on extra threads that serve no purpose. The same applies to older generations. Get the i5-XXXXK. Get faster memory, not higher capacity memory. I'm currently using 125MB on two LL's and two DC's. 32 GB would serve no purpose. The more efficient power supplies are more important if you're going to run a heavy GPU as well. Where the CPU might draw at most 60W-80W, a GPU can pull 150W-300W depending on what you get. A PSU that is 80% efficient and requiring 100W draws 125W at the wall. The 25W loss equates to 1 kWh after 40 hours which comes to between 4 and 5 kWh per week, anywhere from $0.50 to $0.75 per week. That's $25 - $40 per year. A PSU that is 85% efficient requiring 100W draws only 117.6W at the wall, but the 7.4W difference could be $7 - $10 per year. If your system requires 300W instead, triple that amount. The motherboard need only be powerful enough to support your hardware. I can vouch for ASUS boards being able to give a CPU enough of an overclock to keep 2400 MHz memory bottlenecked. If overclocking, you want to make sure the motherboard is capable of supplying that much power to the CPU, and most boards probably can. I'll leave the discussion of the "best" GPU to buy to someone else. Used hardware isn't my area of expertise but I know it's the best place to go.

2014-11-28, 15:31	#3
Dubslow Basketry That Evening! "Bunslow the Bold" Jun 2011 40<A<43 -89<O<-88 3·29·83 Posts	It might be worth waiting for Broadwell in a few months, or longer for DDR4 memory.

2014-11-28, 16:14	#4
fivemack (loop (#_fork)) Feb 2006 Cambridge, England 2³·11·73 Posts	I'm not expecting Broadwell to be excitingly much faster, except conceivably on the models with L4 cache. The better Broadwell multiplier might be good for TF, but if you are doing TF on CPUs you have already left the path of wisdom. For current hardware details I would agree with TheMawn, and would say either to buy now or to wait a year or so for the Sky Lake/K models with 512-bit-wide AVX and large L4 cache to exist and for George to get the Prime95 code to work well on them.

2014-11-28, 17:31	#6
fivemack (loop (#_fork)) Feb 2006 Cambridge, England 2³×11×73 Posts	Given the price of DDR4 memory, the price of X99 motherboards, and the need for a GPU, I haven't found a 5820K system which is cheaper than two i5-4670K systems.