WTF is going on with SLI?
Linus Tech Tips
·Linus Tech Tips
·2017-05-06
·
1,505 words · ~7 min read
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a few weeks ago I was sitting in my office reading through a white paper
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from NVIDIA in order to make a video for you guys that would simplify and answer
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all the crazy questions people had about
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the new multi-GPU and SLI configurations for the 1000 series and direct X12 era
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armed with the white paper I thought this would be an easy task but within an
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hour or two I was collapsed onto my desk contemplating the sheer futility of life
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since then I have received answers to my multiple horrendously long emails to
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NVIDIA ones that hopefully will allow me
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to shed some light on what the hell is
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going
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on cooler Masters masterc case maker 5
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features their free form modular system which allows you to customize adjust and
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upgrade make it yours at the link in the video description down below first first
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things first the question that has been hotly debated since the keynote where
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they announced the GTX 1080 and 1070 is
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three and four-way SLI still a
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thing no not for gaming only
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specifically overclocking and benchmarking applications like fire
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strike Catzilla Etc that's it I'm not
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even upset I like this move three and four-way SLI are and have been always
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such an unjustified viable configuration that telling people very directly not to
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do it and going even further by not supporting it contributes nothing to
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NVIDIA's bottom line and saves people from lighting their money on fire good
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guy NVIDIA but all of that said and this adds a lot of confusion to the topic you
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can still play games with three or four graphics cards and you can use the
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performance of all of them together just
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not in classic S Mode this can be done with MDA mode also
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known as multi-display adapter mode or through LDA explicit also known as link
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display adapter explicit mode two different methods of GPU cooperation
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that are at least somewhat separate from LDA implicit mode which is what NVIDIA
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will be using for SLI what okay I'll get
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more into those specifics later it's not that bad but here we go basically game
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designers can explicitly code any degree of multi-GPU support for their games
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including three and four-way NVIDIA Solutions but please note that because
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this responsibility lies with the developers don't expect it to happen
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much back to the modes which one is best out of the three great question and I
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can confidently tell you that we don't know yet I don't have enough stuff to
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test and in asking NVIDIA their official response was that they don't have enough
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data yet and they need more dx12 multi-GPU enabled games notice that that
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part about developers probably not doing it much uh in order to make any sort of
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qualitative determination which also means that no there will be no
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benchmarks in this video that will come later but I do have many more
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interesting things to say so I would I would I would stay so here's what we do
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know NVIDIA's new high bandwidth SLI bridge is not required you do need it
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for 5K gaming and Surround gaming but if you have one of those fancy LED Bridges
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you're fine for for 4K gaming and 2560 X 1440p gaming at 120 HZ and you have a
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standard Bridge you can take another step down and do 2560 X 1440p at 60 htz
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and 19 20 x 1080 gaming yeah NVIDIA will
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automatically notify you that your bridge is not good enough if you try to
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push it to a setup that is outside of those specifications so I wouldn't worry
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about it much plug everything in see if it works if it does you're good if it
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doesn't they'll tell you and you can fix it pretty easily but Luke you lie they
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were saying things about Enthusiast key that would allow us to unlock three and
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four-way stuff that software unlock does not exist NVIDIA killed it that was fast
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and given how clear I've made my position on the merits of greater than
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two-way SLI it should come as no surprise that I think it's a good thing
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but I also didn't buy three or four graphics cards already based on a
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promise that NVIDIA made that they would all work together with this thing called
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Enthusiast key I feel like that while a number of customers were impacted by
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this is probably fairly low these individuals would represent the most di
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hard of the DI hard NVIDIA fans and gaming enthusiasts and they should
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probably have it made up to them in some way just saying all right but hold up
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let's take a few steps back how exactly does this MDA and LDA mode thing work
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well when s is disabled in the NVIDIA control panel your cards will be running
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in MDA mode MDA is Microsoft allowing
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any set of gpus to be used including cross brand so theoretically you can use
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an AMD card and an NVIDIA card and have them be all over the place in terms of
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tiers and stuff and it should work you can do this all at the same time
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directx12 new feature named shared fences allows for the synchronized
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commands to the various gpus and said gpus will be able to share a pool of
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memory which resides in system memory all that kind of stuff is cool
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when SLI is enabled however your setup will be in LDA mode another Microsoft
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Technology the sub mode LDA implicit
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allows you to use the SLI bridge to transfer display data between gpus
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without interference caused from other agents activity on PCIe and should
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through this clearer communication method allow for additional capabilities
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by utilizing the bridge but we'll have to wait and see uh what the impact is of
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that while in LDA mode if the the games are coded to support explicit multi GPU
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they will be able to scale however well
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with the amount of cards you have in the system without using the SLI Bridge
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again we'll have to wait to see how well this works but this would theoretically
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allow you more than two cards and that's
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basically all we have to work with at the moment we will have to wait and see
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how MDA and LDA explicit modes handle
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regular two-way operation compared to traditional SLI and what the three and
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four-way situation ends up looking like so here's the final word if you want to
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play games with your setup and aren't interested in just rerunning the same
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freaking benchmarking programs on the same freaking setup all day you should
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probably stick with a maximum of two cards and which mode works best will be
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heavily dependent on the game or application you're using oh and I guess
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you could run two in SLI and a third for physics if you just really hate your
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liked this video and like spending your money at least somewhat intelligently
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hit that like button if you dislike this video and you're like the Joker in that
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one Batman movie when he lights the entire pile of money on fire that was
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actually pretty sick if you're more like that you can dislike the video if you
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against you that's fine uh if you want to jump on the Forum to discuss
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everything I said on here and uh argue about things please argue like in a
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friendly way discuss if you want to discuss things become a member on the
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Forum and if you want to see overclocking on GTX 1080 cuz it's like
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weird and there's like P per voltage Point offset stuff click here cuz that's
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another video that's like a little Advanced and interesting and NVIDIA
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changes a bunch of stuff and I'm I'm going to go have a nap