CPU for SLI

[DewisLavid]

Hi, if i was to run two GTX 1070's in SLI will i need to have a higher end CPU and if so what would you recommend for under $250?

[Fasauceome]

we have no idea what you're currently using, or your performance target, or what games you're playing. Also your PSU has to be of good quality.

 

On top of all that, SLI often has quite poor gains (if any) for the added cost and power consumption, not to mention thermal problems. unless you absolutely love the look of two GPUs and that's really what you want, you should consider a single powerful GPU like a 2080 super.

[Pixel5]

you most certainly simply dont want to run SLI with a mid range CPU.

If you wanna take full advantage of the SLI you want to have a motherboard and CPU that can offer 16 full PCI-E 3.0 lanes for each GPU.

which basically means you want to go with AMD but even there you are pretty limited beside the threadripper range in teams of available PCI-E lanes.

[zassou]

....aaand while threadripper have enough lanes for 2 gpus, you don't and probably wont in the near future, have a game that somehow satuated a pcie 3.0 x16 port and require another gpu to process additional graphic stuff, if there is any; games are choking on gpu performance, not transfer speed. besides, threadrippers are designed for professional workloads, they are in no position to compete with gaming cpus like ryzen 7 and core i7/i9 due to higher latency and low frequency. certainy not with it's ridiculous prices.

 

and on top of that, there will be a new generation of graphics cards come around and performed almost twice as good as gtx1070 while way better in effeciency and the most of them all: no compatibility issues.

 

bottomline: DON'T DO SLI, IT'S BAD

[Dravinian]

47 minutes ago, Pixel5 said:

you most certainly simply dont want to run SLI with a mid range CPU.

If you wanna take full advantage of the SLI you want to have a motherboard and CPU that can offer 16 full PCI-E 3.0 lanes for each GPU.

which basically means you want to go with AMD but even there you are pretty limited beside the threadripper range in teams of available PCI-E lanes.

I don't know how true this is - but I am no expert in these matters.

 

What I thought, is that one GPU is a master and one is a slave in the SLI configuration so they are not both sending data through the PCIE slot, they are sending data between themselves through the SLI bridge - which is why the SLI bridge is important.

 

Also, I have an i7-4790k, on a maximus ranger VII motherboard, from 6 years ago.  It offers a full 16 PCIE 3.0 lanes....total.  Not for each GPU.

 

Yet, there are games that will not load with a single GTX 970.  Shadow of the Tomb Raider specifically.  It will load with two GTX 970s in SLI.

 

So clearly the SLI is doing something, and I don't have the PCIE lanes to support it?

[Pixel5]

1 hour ago, Dravinian said:

I don't know how true this is - but I am no expert in these matters.

 

What I thought, is that one GPU is a master and one is a slave in the SLI configuration so they are not both sending data through the PCIE slot, they are sending data between themselves through the SLI bridge - which is why the SLI bridge is important.

 

Also, I have an i7-4790k, on a maximus ranger VII motherboard, from 6 years ago.  It offers a full 16 PCIE 3.0 lanes....total.  Not for each GPU.

 

Yet, there are games that will not load with a single GTX 970.  Shadow of the Tomb Raider specifically.  It will load with two GTX 970s in SLI.

 

So clearly the SLI is doing something, and I don't have the PCIE lanes to support it?

SLi does work with only 16 PCI e lanes but both GPUs will each only have half the bandwidth they would normally have.

A 970 is too slow to be affected by this but if you go for higher end cards the bandwidth will cost you FPS which is one of the reasons why going for SLI usually does not double your FPS.

[Dravinian]

8 minutes ago, Pixel5 said:

SLi does work with only 16 PCI e lanes but both GPUs will each only have half the bandwidth they would normally have.

A 970 is too slow to be affected by this but if you go for higher end cards the bandwidth will cost you FPS which is one of the reasons why going for SLI usually does not double your FPS.

I thought that was to do with the fact that SLI didn't double the RAM on the GPU.  So if you have two 4gb cards, you don't get 8gb of RAM, you get 4gb of RAM.

 

Also, last year GN did a video on 2080 ti, on NVLink on x16/x16 and x16/x8 and on x8/x8.

 

Game test shows:

127.2 fps at x16/x16

125.1 fps at x16/x8

106.9 fps at x8/x8

 

So yes, two x8 will be problematic for faster cards.  But x16/x8 doesn't appear to show any difference at all in real terms.

 

Synthetic test shows:

82.3 fps at x16/x16

82.0 fps at x16/x8

82.1 fps at x8/x8

 

Using 2080 ti GPUs on NVLink even x8/x8 didn't appear to show any difference.

 

I am not suggesting SLI is worth it, I really don't think it is worth investing in a second card, it is a pretty dead technology route now.

 

Just trying to understand the tech behind it.