The high bandwidth SLI bridges can make an enormous difference with GTX 1080 SLI at 4k

[SteveGrabowski0]

in comparison to using the cheap flexible SLI bridges that come with SLI capable boards, according to benchmarks from Hardware Unboxed. I guess retiring the 3-way and 4-way SLI support makes sense when these fingers can be used much more efficiently for dual card SLI.

 

 

[LabRat]

techpowerup has a little on that in this article that contradicts any great advantage, or any advantage.

http://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1080_SLI/

 

why don't I see a link?

[RyGuy99]

My question is why are SLI bridges just a thing. 

[Zyndo]

1 minute ago, RyGuy99 said:

My question is why are SLI bridges just a thing. 

It allows the cards to better communicate with each other without having to flood the motherboards existing lanes with unnecessary data.

[RyGuy99]

4 minutes ago, Zyndo said:

It allows the cards to better communicate with each other without having to flood the motherboards existing lanes with unnecessary data.

It's inefficient in it's own right though. It would be much better using those motherboard lanes that most people don't even use up in the first place.

[SteveGrabowski0]

17 minutes ago, LabRat said:

techpowerup has a little on that in this article that contradicts any great advantage, or any advantage.

http://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1080_SLI/

 

why don't I see a link?

Their results are terrible. They tested one modern game at 4k, Rise of Tomb Raider, and did it in DX12 where there is no SLI scaling whatsoever. Battlefield 3, WOW are stupid games to test and testing Black Ops 3 at only 1600x900 doesn't make any sense. Techpowerup's result contradicts nothing from the Hardware Unboxed benchmark.

[LabRat]

still don't see a link to the data.

[Big-G]

1 hour ago, RyGuy99 said:

It's inefficient in it's own right though. It would be much better using those motherboard lanes that most people don't even use up in the first place.

And it's a AMD patented process... Nvidia can't use it....

[RyGuy99]

1 minute ago, GidonsClaw said:

And it's a AMD patented process... Nvidia can't use it....

I didn't know that. Many tech journalists must not know that either because they keep complaining about SLI bridges. Heck even linus did last year for the 900 series!

[BrightCandle]

That is very interesting. I would have expected mostly differences appearing in the FCAT results (which pcper hasn't published yet) rather than in actual FPS numbers, to see any difference at all is a surprise. If I was to take a guess as to what is going on it would be that in 4k the frames transferred over PCI-E are competing with the games use of the bus and those games that use the bus more fully will be impacted more by the contention. But perhaps there is a second effect and impact on the primary card also handling the secondary cards images and that only impacts on certain games usage of the cards.

 

4k at 100 fps is 2.3 GB/s and a 16x slot has 15.75 GB/s total but since this test was done with Z170 he only has 8x on both cards so 7.88GB/S theoretical maximum, that 2.3GB/s of image traffic is substantial compared to the available bandwidth. But the losses from going across PCI-E in some cases are much larger than 2.3/7.88 = 28%.

 

The issue I suspect is potentially priority, the cards traffic gets held up and held behind traffic from the CPU and isn't switched fairly and has to wait and this causes additional delay in the frame scanning out over and above the time of just transferring the bytes, in effect it doesn't get to just use 28% of the transfer when it wants its getting slowed down scanning out and this is holding up that secondary card. Then the frame rate smoothing algorithm kicks in reducing the primary card down in fps as well to avoid microstutter and the combination doubles the impact of the cost of contention, decreasing performance dramatically as scan out is held up.

 

But once you have two bridges in place/high bandwidth then you have sufficient bandwidth to keep transferring the images directly to the display port from the secondary card over the bridges so it doesn't go across PCI-E and hence there is no impact and hence performance is dramatically better.

 

I think these particular high impact games would be interesting tested on 16x and 8x handware to see whether they gain from being on an X99 as well.

[NowThatsDamp]

I'm just glad to hear that 2-way SLI has a bright future of actually working

[l__T__l]

6 hours ago, LabRat said:

still don't see a link to the data.

Did you watch the video? It has benchmarks in it.

[LabRat]

what part of "i don't see a link" didn't you read? i don't see anything but but a small written description in your opener. it's either not there or the link is full of adware and my machine won't load it.