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Old 2021-07-25, 12:11   #8
drkirkby
 
"David Kirkby"
Jan 2021
Althorne, Essex, UK

3·149 Posts
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Quote:
Originally Posted by kriesel View Post
RTX 3080 Ti is fast at ~4800 GHD/d in TF, but at ~93. GHD/day for PRP, LL or P-1, is comparable to a GTX 1080 Ti or RX 5500 XT or ~30% of an RX 6900XT or Radeon VII per https://www.mersenne.ca/cudalucas.php
I have multiple Radeon VIIs on a system served by a Celeron G1840, so yes it does not take much CPU to keep GPU apps going. Except when doing GCDs in P-1. I recommend about as many physical CPU cores as GPUs & HT so the GPUs are unlikely to wait for each other. Also >16GB of system ram if doing a lot of GPU P-1 on multiple 16GB-vram GPUs simultaneously.
I have a few questions about that table
  1. What is the point of listing (GHd)2/W? I must be overlooking something, but I can't see what useful information that gives.
  2. What is JVR?
  3. What is JVR2?
The 300 W Radeon VII gives 1.053 GHz day/W. That's more power hungry than my 8167M CPUs. I reckon I get about 240 GHd/day from one of those, which at 165 W TDP is 1.45 GHd/W. I will need to double-check that 240 GHd/day as I have stopped mprime several times to play around with it, but I'm pretty sure it is more power efficient than 1.053 GHz day/W, based on its TDP. However, I'm feeding about 490 W into the UPS when running a couple of 8167Ms flat out, which is rather more than 2*165=330 W. There are some obvious losses
  • UPS efficiency.
  • Motherboard
  • Fans
  • PSU
  • Disks - one is a mechanical hard drive, which I guess I should remove as I am not using it.
  • GPU (75 W, but virtually idle).
  • Quad Ethernet card - I should remove that, but need to add a GPIB controller card.
The basic PC with 16 GB RAM and 8-core 2.1 GHz CPU was $1100. The 8167Ms were £300 (about $413) used each. Since it needs ECC RAM, that gets expensive, although I still have the Dell RAM and CPU that I should sell.
For PRP tests it is not clear the GPU wins, but for trial-factoring the CPUs are not good.
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