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[TPU] NVIDIA GeForce GTX 1080 SLI (Is the SLI HB Bridge essential?)

post #1 of 53
Thread Starter 
http://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1080_SLI/
Quote:
At close to $1,400 (as low as $1,200 if you consider the $599 baseline price, and $1,300 if you consider the $650 mean price of custom-design cards), the GeForce GTX 1080 SLI is the fastest dual-GPU solution, although any claims of being the fastest graphics solution money can buy could be disputed by the fact that the GeForce GTX Titan X and the Radeon R9 Fury X support 4-way multi-GPU.

The GTX 1080 duo makes short work of any current game at 4K Ultra HD resolution, with framerates exceeding 60 FPS in most games that scale. 4K@60 Hz is also the highest monitor resolution we had at hand. NVIDIA's decision to facilitate higher resolutions such as 5K and 4K@120 using modern DisplayPort 1.4 connectors, and the new SLI HB multi-GPU interconnect with over three times the bandwidth of a classic 2-way SLI bridge, shows that the company believes that the GTX 1080 SLI can provide playable frame-rates at those resolutions.

A GeForce GTX 1080 SLI setup should prove useful if you have a 120 Hz WQHD (2560 x 1440) monitor. For a 60 Hz monitor, even a single card is sufficient, as its framerates stay close to or exceed 60 FPS in most of the titles. The GTX 1080 SLI is way overkill for lower resolutions such as 1080p. Even a single card is overkill for 1080p. Get a GTX 970 or wait for the likes of the AMD Radeon RX 480.

2-way multi-GPU users (typically gamers) is a significantly larger demographic than 3-way and 4-way multi-GPU users (typically enthusiasts). This is also supported by the fact that you needed the costlier HEDT platform for enough PCIe slots for 3-way/4-way. With GTX 1080, you're getting smooth frame-rates (60 FPS and above) with just two cards, which brings 4K@60Hz performance within the realm of gamers. You needed 3-4 GTX 980 Ti cards to achieve something like this before, and the demographic was smaller.

When you look online for guidance on SLI HB, you will find forums full of people claiming that you must absolutely use a high-bandwidth bridge with Pascal, or performance will suffer. We took a special look at that, comparing performance of the classic SLI bridge with the HB bridge, at up to 4K60, and there is no significant difference in framerates or visual smoothness, not even at games running over 200 FPS at 4K resolution.

The underlying reason is that SLI works on a display controller level, which is also why G-Sync uses SLI logic - which can do variable frame rates. Not every single frame that is rendered in AFR gets sent over the SLI bus. Rather each GPU renders into a single buffer (overwriting it), and SLI will pick up a frame from the second card when it's time to send a frame to the monitor, which happens at 1/2 the monitor refresh rate (the primary GPU provides the other half of the frames).

A single frame at 4K resolution is 32 MB (3840x2160x4 bytes per pixel), at 30 frames per second that's 960 MB, which is just shy of the 1 GB/s bandwidth that classic SLI provides. This means that SLI HB provides no benefit until you exceed that limit, which happens at higher resolutions like 5K or 4K@120. However, even when bandwidth is exceeded you will not run at reduced framerate, rather you will see stuttering on the monitor: the second GPU sends its frame over the SLI bus, but due to bandwidth limitation it will arrive too late to be sent to the monitor, so it has to wait its turn, which is two refreshes, causing the frames to be displayed on the wrong order, which you see as stuttering.

Right now SLI HB bridges cost $39.99 and are in limited supply, especially the popular three-slot bridge, which most motherboards use. So as long as you are gaming on 4K with 60 Hz or lower resolution/refresh rate you will be fine with a classic bridge, which also has the advantage that it is flexible, which lets you pair cards that have the SLI connectors at different vertical positions.

The GTX 1080 SLI cannot escape the biggest limitation of multi-GPU setups since the dawn of time - software support. There continue to be big AAA game titles (5 out of 16 in our testing) that lack SLI support due to engine limitations, which NVIDIA cannot fix through a driver update. More and more modern game engines come with such caveats, which is why classic AFR frame rendering doesn't have much of a future looking forward.

With the advent of DirectX12 we are promised new multi-GPU rendering modes thanks to Microsoft giving developers more control over per-GPU resource allocation, but we doubt that we'll see widespread use of these techniques. Nowadays games are developed for consoles first (which are single-GPU), and publishers have little interest to spend a lot of developer time (= money) on adding support for exotic multi-GPU configurations that are used by only a small percentage of their customers.

The enthusiasts among you will be pleased to know that 3-way and 4-way SLI, using classic bridges may still work on a very few synthetic benchmarks, such as 3DMark FireStrike, Catzilla, Unigine Heaven, etc. Such machines will work like a machine with 2-way classic-bridge SLI on every other app such as games.

Therefore, for now we recommend that unless you really need the muscle-power of two GTX 1080 in your display setup, wait things out till there are bigger GPUs based on this architecture, which can tame those resolutions with a single chip.





Is the SLI HB Bridge essential?



post #2 of 53
of course the difference is negligible.i'm not going to buy this bridge for performance gain but for the way it ties the looks of 2 FE cards together.
post #3 of 53
The nVidia HB SLI Bridge is incompatible with EK water blocks. They may be releasing an HB SLI bridge of their own, and there will be partner bridges as well.

It doesn't look like there's any performance impact at the resolutions tested anyway, luckily.
post #4 of 53
SLI scaling has become completely abysmal... there really is very little point in it anymore. 58% scaling at 4k after factoring out the games which don't scale? Absolutely horrid. thumbsdownsmileyanim.gif

Can't wait until we have a single GPU solution that can truly handle 4k 60 gaming without compromise... perhaps the 1080 Ti.

At least one good piece of info came from this... the HB SLI bridge is pure hype.
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post #5 of 53
Quote:
Originally Posted by BigMack70 View Post

SLI scaling has become completely abysmal... there really is very little point in it anymore. 58% scaling at 4k after factoring out the games which don't scale? Absolutely horrid. thumbsdownsmileyanim.gif

Can't wait until we have a single GPU solution that can truly handle 4k 60 gaming without compromise... perhaps the 1080 Ti.

At least one good piece of info came from this... the HB SLI bridge is pure hype.

Out of curiosity, what was hyped?
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post #6 of 53
Quote:
Originally Posted by axiumone View Post

Out of curiosity, what was hyped?

The idea that the HB bridge would somehow magically improve the awful 2 way scaling for SLI that we've been seeing in recent years.
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post #7 of 53
Quote:
Originally Posted by BigMack70 View Post

The idea that the HB bridge would somehow magically improve the awful 2 way scaling for SLI that we've been seeing in recent years.

Why would that be the case though? The only thing nvidia showed in it's press slides is improved frametime variance in one game. There has been no indication stated or implied that scaling or performance would improve in any other way.
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post #8 of 53
Thread Starter 
Quote:
Originally Posted by axiumone View Post

Out of curiosity, what was hyped?

post #9 of 53
Quote:
Originally Posted by BigMack70 View Post

The idea that the HB bridge would somehow magically improve the awful 2 way scaling for SLI that we've been seeing in recent years.
no. its for 4k, 5k and surround at high refresh rate.
someone already posted above lol
post #10 of 53
Quote:
Originally Posted by ondoy View Post


I think even more absurd is the "LEDs make it go faster" line in that chart...

Maybe AMD can do go fasta red paint rolleyes.gif
Edited by CasualCat - 6/21/16 at 7:49am
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