mfaktc and PCIe bus width

[Chuck]

I was thinking about adding a second GPU; the two 16-lane PCIe slots on my motherboard are next to each other and I would really like to space the GPUs further apart for better heat dissipation.

The third PCIe slot can only run with 8 lanes. With the GPU sieving version of mfaktc, would this make any difference in the performance of the program?

[Xyzzy]

We tested this in our computer and there was no difference in throughput.

We tested "top/middle", "top/bottom" and "middle/bottom".

We tested three cards also but our third card is slow (GT 430) so we are not sure if three fast cards would be an issue.

[swl551]

Originally Posted by Chuck

I was thinking about adding a second GPU; the two 16-lane PCIe slots on my motherboard are next to each other and I would really like to space the GPUs further apart for better heat dissipation.

The third PCIe slot can only run with 8 lanes. With the GPU sieving version of mfaktc, would this make any difference in the performance of the program?

I had terrible performance by not using the designated slots. the MOBO instructions often states specific slot loading.

Sadly two card next to each other (gtx-570s) caused the top card to be heat loaded by the lower card.... It didn't go so well.... Enter liquid cooling.

Also if you OC the cards you will see a significant increase in power consumption. A 600 watt PS will likely need to be 1000 watt... Where's FlashJH when we need him to tell his horror stories....

[henryzz]

I have a similar question but slightly more extreme. I have been thinking of getting a graphics card at some point something like a 740 when they come out eventually. The card will be designed for 16x with PCIe 3.0 but my motherboard only has PCIe 1.1. I know 2.0 cards should run on my system at an equivalent bus speed of 16x 1.1 or 8x 2.0. Would a PCI 3.0 card run at 4x 3.0 speeds? Would it run at all?
The motherboard is an ASUS P5K-VM if that helps. I will be wanting to use it for a variety of stuff including things like cudalucas, gpu-ecm, gpu P-1 etc.

[chalsall]

Originally Posted by Xyzzy

..."top/bottom"...

Which did you prefer?

[Chuck]

Originally Posted by Xyzzy

We tested this in our computer and there was no difference in throughput.

We tested "top/middle", "top/bottom" and "middle/bottom".

We tested three cards also but our third card is slow (GT 430) so we are not sure if three fast cards would be an issue.

My computer has the Raven-style case so it would be "left", "center", and "right".

[Chuck]

Originally Posted by swl551

I had terrible performance by not using the designated slots. the MOBO instructions often states specific slot loading.

The MOBO (Asus P6X58D Premium) instructions say the third slot can be configured as 8 lanes, with the trade-off that the middle slot (which would be unused) would then also use 8 lanes. With the middle one at 16, then the third can only run at 1 lane.

[swl551]

Originally Posted by Chuck

My computer has the Raven-style case so it would be "left", "center", and "right".

Sounds like it time to try it and see what happens. Everything else is just speculation. (probably good speculation, but it is your stuff)

[Aramis Wyler]

Originally Posted by henryzz

I have a similar question but slightly more extreme. I have been thinking of getting a graphics card at some point something like a 740 when they come out eventually. The card will be designed for 16x with PCIe 3.0 but my motherboard only has PCIe 1.1. I know 2.0 cards should run on my system at an equivalent bus speed of 16x 1.1 or 8x 2.0. Would a PCI 3.0 card run at 4x 3.0 speeds? Would it run at all?

A co-worker of mine tried running pci 3.0 cards in 2.0 slots. The board was solid and could handle 2x16, not one of the boards that can do 1x16 or 2x8. Even so, the PCI 3.0 card wouldn't run in it. They say they are backwards compatible (usually with a *) but the truth is it's really hit and miss if a 3.0 card will run in a 2.0 slot. If it will run, it will almost certainly run slower than it would in a 3.0 slot not because of the channels/bandwidth but because of the clock speeds. Personally I'd reccomend getting a higher end 500 series 2.0 card than a lower end 700 series 3.0 card unless you are looking for a good excuse to replace the motherboard.

Regarding the Chuck's sitation, the 8x or 16x bandwidth won't matter at all, but the board configuration might. Make sure the mboard doesn't mind running 1 and 3 w/o 2. You might be suprised to find out that if you do run 1 and 3 w/o 2, they'll both run at full 16x speed anyway.

EDIT: For reference, I run an overclocked 480 and and overclocked 580 on an ASUS board with a 750 watt power supply.

[paulunderwood]

Chuck could use a riser card or ribbon

[Chuck]

Originally Posted by paulunderwood

Chuck could use a riser card or ribbon

Now this is a great idea; something I never thought of.