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Author Topic: CPU effect on 2x 6870 mining operation?  (Read 1110 times)
zombo
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June 14, 2011, 04:00:58 AM
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Hi guys,

I have the choice of using either an old Intel E2140 low power cpu or an E5300 slightly newer but I assume uses more power CPU.

Is there any benefit performance wise going to the e5300 or should I stay with the 2140 and save $$$ on power?
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swusc2
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June 14, 2011, 04:03:29 AM
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No reason to upgrade your CPU if the rig is purely for mining. Many people including myself run 4+ cards off a single core sempron 140

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zombo
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June 14, 2011, 04:04:22 AM
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Thanks for your advice Smiley Just keen to get out as many Mhashes as possible with my hardware I have available!
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June 14, 2011, 04:09:38 AM
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basically as i understand it the cpu is only there to run the os the gpu's do the work as they are designed for stream processing where as a cpu is designed for thread processing so as long as your rig has enough cpu to run the board then you are golden

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lessPlastic
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June 14, 2011, 04:14:33 AM
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Some people (like me) like to run the CPU as well, there's no reason not to and you're gonna be getting 2 - 4 MH/s on a modern fast CPU. Even if you mine at 400 MH/s that's still +1%. It's up to each person though. Every little bit counts.
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June 14, 2011, 04:19:35 AM
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The trade off to the 2-4MH/s part is that your power consumption jumps even more. You may want to see what your power consumption is with and without the CPU going balls out... Becaue 2-4MH/s at an extra .1kwhs adds up over months of time... especially considering a GPU is far more efficient (6xxx and 5xxx) per kwh.

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June 14, 2011, 04:23:16 AM
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when i first started mining i thought to myself well my vid card is doing all the work and my cpu is just sitting there. so i made my cpu a worker also and it dropped the output my gpu signifigantly. The only way i could see a benefit of using a cpu to mine is if you had a pile of them laying around and doing nothing and only if you didnt have to pay for the electricity to run them. I think a cpu would be hard pressed to generate enough BTC to cover kwh costs

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June 14, 2011, 04:36:18 AM
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I wouldn't touch the CPU.

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June 14, 2011, 05:01:56 AM
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You don't want to mine on a CPU because the cost of the extra few Mhash doesn't come close to playing the extra power used by the CPU to mine. If you don't have to pay for power then go ahead.

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June 14, 2011, 05:04:23 AM
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Exactly... that CPU mining can use 100w/hr easily... more if its a 4-6core behemoth... not a very efficient way to mine. It's why Botnets tend not to have the power to challenge 'honest' systems in generating current Blocks / etc. The systems tend not to have the gpgpu HP.

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TheMartin
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June 14, 2011, 05:13:02 AM
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Hi guys,

I have the choice of using either an old Intel E2140 low power cpu or an E5300 slightly newer but I assume uses more power CPU.

Is there any benefit performance wise going to the e5300 or should I stay with the 2140 and save $$$ on power?

In principle the CPU doesn't matter. Any CPU will be good for GPU mining, and GPU mining only makes sense.

But perhaps you will see an indirect effect when using more than one GPU on a single board.

In this case your CPU might be 100% busy because the newest version of the underlying openGL is broken for multi GPU systems.

Even though performance for a multi GPU system usually can't be increased by upgrading to a better CPU, as openGL will keep any CPU 100% busy.

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June 14, 2011, 05:26:35 AM
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I ususally run a cheap dual core

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June 14, 2011, 05:35:44 AM
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I ususally run a cheap dual core

That cheap dual core, unless you live in a college dorm, or don't have to pay for electricity, costs you more money in electricity bills then it will make for you. And if you are living under your parents roof. It costs them more money then you will make from that CPU.

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phorensic
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June 14, 2011, 07:23:57 AM
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I ususally run a cheap dual core

That cheap dual core, unless you live in a college dorm, or don't have to pay for electricity, costs you more money in electricity bills then it will make for you. And if you are living under your parents roof. It costs them more money then you will make from that CPU.
He meant just to get the system running.  Not to mine on the CPU.
CoolHand144
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June 14, 2011, 07:29:49 AM
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What i did was Get a MoBo that has the AM2, AM2+ and AM3 compatibility but also have multiple PCI-e 16x 2.0 slots so if i wanted to upgrade later i can.  even though you dont need the 2.0 slots to run a number of cards you are going to see about a 20% bottlenecking from the 1.0 slots.
This way you can put a cheaper CPU in for now but if you wanted to add a better one later you can.

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June 15, 2011, 12:04:28 AM
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I have an i7 940 running at 2.93Ghz which I bought about a year ago.  I can up my Mhash/s production by about 19-20 if I use the CPU to mine also, and my power usage goes from 320 Watts to 436 Watts.  That's a difference of 116 Watts, or 0.116 kW.  Multiplied by 24 x 30.4166666, (30.4167 being the number of days per month on a non-leap year: 365/12) that gives 33.872 KWh for a month.  My electricity cost is 0.0985$/Kwh, so it would cost me about 3.34$ / month to run my CPU at 100%.

19-20 Mhash/s would probably pay more than the 3.34$/month, but I find the amount of heat generated a bit troubling, and I honestly don't know how long that CPU would last running at 100% like that 24/7.

So money-wise it's probably worth mining with a good CPU, but it would be much slower to pay-off than a GPU, and generate a whole lot of heat which you need to dissipate somehow (fans, A/C?).  Next winter, though, I might switch over to a computer-powered heating system for the apartment Smiley
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