CPU Processor choice as regards GPU

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CPU Processor choice as regards GPU

Postby KA1J » Thu May 28, 2020 5:01 pm

I have an 8th generation Intel motherboard which only accepts an 8th generation processor, for example i5-8400, the 4 digit starts with an 8. I have 8 Gigs of lower speed DDR4 ram in it and I don't plan to overclock the CPU, but it needs a CPU.

I am going to try Linux on this board & use it solely for folding.

I haven't decided which folding oriented GPUs will go into it but at a minimum will be a pair of RTX 2060 KO, possibly the 2080 variety.

Before picking one up I should ask if there is a minimum value I need to have; speed, cores, anything? I3 vs i5, i7, Celeron, default speed core, boost speed value, anything?

I'll dedicate 1/2 of the cores to folding.

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Re: CPU Processor choice as regards GPU

Postby JimboPalmer » Thu May 28, 2020 6:11 pm

If you have two GPUs, that will need two threads, even before any CPU folding.
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Re: CPU Processor choice as regards GPU

Postby markdotgooley » Thu May 28, 2020 6:13 pm

I had a Linux box with an old 4-core i7, about 9 years old. But I wasn't sure about power consumption and compatibility with recent GPUs -- probably both nothing to worry about -- so I spent nearly US$200 on a Ryzen 5 1600 AF (at the time only US$85, cooler included, 6 cores, 65W rated power consumption) and a compatible ATX motherboard. Updated Linux to latest LTS version.

Initially I spent US$350 on an ordinary 2060. Worked fine. CPU seemed much more than necessary. 2060 ran under 70C in the slightly cramped case. Later I wanted to add a 2060 KO (US$300) but the power supply didn't have enough connectors and I wasn't sure it had a high enough rating to use a splitter and power both GPUs. I ended up buying a 750W power supply, a bigger case, a few extra case fans, as well as the KO... the money added up to a bit much.

Anyway, with the 2060KO on the main x16 slot (faster) and the old 2060 on the secondary (slower), the CPU still seems far more than I need. Right now I'm using 4 CPU cores (8 threads) for folding, but using 5 (10 threads) seemed to work just as well for handling the GPUs. Cards both run between 60C and 80C (the KO is higher in the case and usually around 75C, the regular 2060 lower and usually around 65C). For some reason the KO usually shows a GPU utilization near 95% and the other often only around 75% though sometimes higher. The KO usually uses under 35% of its PCIe bandwidth (supposedly 8.0 GT/s maximum), the regular 2060 often 60% to 80% of its maximum 5.0 GT/s. Does lower PCIe bandwidth limit the GPU utilization, even when there seems to be more than enough? I don't know.

My guess is that one thread per GPU even on something like my old core i7-950 Bloomfield (the one I ended up not using) is probably enough, one core per GPU probably too much (but somehow it makes me feel better). PCIe bandwidth is not supposed to matter much under Linux, but if I can trust the GPU Utilization figures I get from the "NVIDIA X Server Settings" application, perhaps it does. (I still have no other ideas why the regular 2060 has consistently lower utilization.)
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Re: CPU Processor choice as regards GPU

Postby kiore » Thu May 28, 2020 6:23 pm

Hi I understand the issue, as noted you would need a least a dual core CPU I understand on Linux this not such an issue but future driver/client changes could change this or you may wish to swap to windows at some point. To give it a bit more future proofing a low power quad core CPU would seem a reasonable choice to give you a general purpose machine, an i3 or 5. You may want to upgrade the RAM at some point which is usually simple enough but changing the CPU more complex.
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Re: CPU Processor choice as regards GPU

Postby Joe_H » Thu May 28, 2020 6:32 pm

Depending on the generation, some of the low end chips such as Celeron may have support for fewer PCIe lanes than your motherboard supports. So check that before selecting a Celeron or Pentium branded processor. Don't know offhand if that is an issue with the 8th generation.

Otherwise, as mentioned you need a CPU thread/core for each CPU. A slow processor may cause the checkpoints/sanity checks to run a bit slower, otherwise any recent processor will be adequate.
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Re: CPU Processor choice as regards GPU

Postby bruce » Thu May 28, 2020 8:15 pm

I'd probably get an i5 or i7 but that's not just to support the GPU. I'd probably do a bit of CPU folding, too. I've never cared for the Celeron but I can't give you a good reason. It seems to us a lot of power and generate a lot of heat, but that's a prejudice, not based on fact.
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Re: CPU Processor choice as regards GPU

Postby NRT_AntiKytherA » Fri May 29, 2020 7:53 am

If you really want the CPU and 2xGPU folding concurrently then even a quad core wouldn't really cut it because you'd only have 2 of the 4 cores folding while the other two would be snaffled up for GPU WU as JimboPalmer points out. Yes there's hyper-threading on some processors but physical cores are always better from a heat (and threat mitigation standpoint given the generation of hardware you are looking at buying - however you could disable all linux kernel mitigations for much better overall system performance if you aren't on a corporate network or in a place where anyone else has physical access to your machine).

TLDR - I'd go hexa or octa core minimum and turn off hyper-threading if you can afford it.
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Re: CPU Processor choice as regards GPU

Postby MeeLee » Fri May 29, 2020 11:07 pm

My recommendation,
A core i3 of at least 2,5Ghz, preferably 3Ghz and 2 slots of pcie 2.0 x8 or more (or 3.0 x4).
Get a quadcore of you later plan om adding a GPU.
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Re: CPU Processor choice as regards GPU

Postby MeeLee » Fri May 29, 2020 11:09 pm

bruce wrote:I'd probably get an i5 or i7 but that's not just to support the GPU. I'd probably do a bit of CPU folding, too. I've never cared for the Celeron but I can't give you a good reason. It seems to us a lot of power and generate a lot of heat, but that's a prejudice, not based on fact.

The Celeron g5000 series come in a 35W and 65W variety, dual core, 3Ghz. Good enough for 2x RTX 2080 GPUs in Linux.
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Re: CPU Processor choice as regards GPU

Postby KA1J » Thu Jun 04, 2020 4:38 pm

Follow-up: I picked up a used i5-8600K on fleabay. I'm not going to overclock the processor though it is one of the overclockable processors. It does not have hyperthreading, the i7 do that, but for my needs it'll be fine.

Thanks for the advice.
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Re: CPU Processor choice as regards GPU

Postby kiore » Thu Jun 04, 2020 6:38 pm

KA1J wrote:Follow-up: I picked up a used i5-8600K on fleabay. I'm not going to overclock the processor though it is one of the overclockable processors. It does not have hyperthreading, the i7 do that, but for my needs it'll be fine.

Thanks for the advice.


This will be plenty to run the GPU and could run a small cpu client as well.
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Re: CPU Processor choice as regards GPU

Postby HaloJones » Sat Jun 06, 2020 1:34 pm

Used B150 motherboard from ebay
Used G440 dual-core from ebay
single stick of DDR4 4GB

that very low spec mobo/cpu/ram is running a Titan X and a 1070 for a current daily ppd of >2.1m. (Linux Mint 18)

You do not need more than two cores if you're running two gpus with no cpu folding. YMMV but cpu folding isn't worth the cost unless you already have a high-core-count cpu.
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