Folding on nVidia GPU's Questions

[sheroo]

OK guys, I have yet more questions... This time specifically about folding on NVidia GPU's.

1. It seems as a rule of thumb (whether under Linux or Windows) that 1 CPU core should be "allocated/available" for each GPU you're folding on. Does this include hyperthreading? i.e. What is the theoretical number of GPU's that a 2600K will support? Could you in theory run 8 NVidia GPU's or are you limited to 4 GPU's matching the 4 physical cores?

2. Does using a Pci-e 1x 16x riser powered cable affect the GPU performance in terms of PPD when folding? (these seem to be used quite a lot in mining rigs so you can space out your GPU's and have up to 6 GPU's hanging off a single motherboard).

EDIT: OK after doing a shed load of research this morning it appears that hyperthreading is counted in the core count. So in theory a 2600K could support 8 GPU's if that were physically possible.

 

[yassarikhan786]

You're spot on about Q1. I have no idea regarding Q2.

 

[kup]

I'd imagine that it would be fine to use risers for the PCIE slots as it seems to have no negative implications for mining.

What are you planning?

 

[sheroo]

I was just casually browsing (as you do), and came across this...

Which lead me onto this...

and these...

And this...

It got me all fired up about building a GPU based folding rig. The motherboard is a steal @ £40...

Just trying to explore the options with NVidia cards and see what else would be required to get it running under Linux.

You'd need an i7 processor, probably 2gb of ram & a small ssd. 6 * 750ti's would be perfect - but they don't work under Linux YET!!

 

[kup]

Oh maaan!! I think you've just mapped out my project for when I move. lol Got a UD9 sat here that I could pop an old i7 in and Fold 7 cards on..

Planning..planning..

 

[hmmblah]

I've wanted to do this for quite awhile now. I've seen these for mining rigs, but haven't seen anyone with a similar setup for folding. With that kind of investment though I didn't want to be a guinea pig. Anyone with disposable income want to step up?

 

[sheroo]

I would love to do this as a long term project. Set it up initially with one gpu, and then add more as the funds became available. The motherboard and risers could be had for around £80. For proof of concept I could use a i3 3220 I have knocking around. I have a spare quality 400W psu for day one & an old sata 2 60GB SSD. The show stopper for me atm is the gpu - which is obviously the main bit...

The 750ti seem like the obvious choice - but they don't work with core 17's atm. So you would get no work under Linux at all. So you'd have to run them under Windows, which only gets core 15's atm, which in turn only gives you 15K PPD - which just isn't worth it atm...

Come on NVidia sort out there drivers so that Maxwell can run core 17's!!!

EDIT:

OK so I've just unearthed another nugget of information from the folding forum regarding my second question...

There are inconsistent observations on the FAH PPD loss caused by the use of pcie 1x extenders.
Some people said the loss is significant, while some others said the loss can be just ignored. Now I find the divergence is probably due to the pcie gen mode that the extender is actually in.
I did a specific test on this several days ago. A same p8900 WU was tested to run on a GTX 660 Ti with three different pcie transfer modes (16x gen2, 1x gen2, and 1x gen1).
And following TPF and PPD results were obtained:


pcie 16x gen2 mode: avg TPF=307.5s, PPD=72.6K
pcie 1x gen2 mode: avg TPF=313.0s, PPD=70.7K
pcie 1x gen1 mode: avg TPF=322.0s, PPD=67.8K

In this observation, the PPD loss for 1x in gen2 mode was only ~3%, while for 1x in gen1 mode the loss increased to ~7%.
I think this result is reasonable since the actual pcie speed in 1x gen1 mode is only 1/2 of that in 1x gen2 mode, that is, 200MB/s vs. 400MB/s. And I also agree that the PPD loss would become more significant with faster gpu cards.

So this would also seem to indicate that re-using an old motherboard with pcie gen1 with a new high end card could lead to a significant loss in PPD....