SLI Performance Scaling - Gaming at 4K Resolution
Linus Tech Tips
·Linus Tech Tips
·2015-05-07
·
1,458 words · ~7 min read
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SLI in a nutshell is a way of using more than one graphics card at a time for a
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richer gaming experience with higher frame rates and more in-game eye candy
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turned on you can learn more about it in this video here on Techquickie now
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NVIDIA's website is full of certain
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information about SLI technology which graphics cards support it where to buy
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the other Hardware you need guides on how to set it up but I noticed that
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Beyond one specific 2-way SLI
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configuration at one specific resolution they don't seem to even want to talk
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about the value proposition of adding in
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more cards or how performance scales in
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relation to the cost as you put more and more graphics cards in your gaming PC so
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when a unique opportunity fell into my lap to test two-way three-way and
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four-way SLI with the brand spanking new gtx980 at 4K I jumped on it
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Corsair gaming RGB keyboards feature Precision Cherry MX RGB key switches for
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16.8 million color per key backlighting for virtually unlimited customization
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click now to learn more I'm going to jump right into numbers here because
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they actually only tell part of the story I tested four games with details
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cranked at 4K resolution on a Gigabyte x99 gaming 5 with a core I 749 30k 6
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core at 4 GHz and 16 gigs of 24 100 MHz
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ddr4 memory and then I threw a Corsair ax 1500i power supply on the bench
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because I was concerned about power consumption and overwhelming the
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existing one but more on that later so
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let's start with what should be the poster child for multi-way SLI Tomb
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Raider 2013 if all you do is hang around and play Tomb Raider go buy 4 GTX 980s
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hell buy an extra one to keep on your desk to remind you of how great it is
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you get 30 FPS average with one card then 20 3 to 24 more frames per second
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with each additional card almost the same scaling going from 1 to two 2 to 3
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and 3 to four cards and on top of that the animations are butter smooth with no
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perceptible micro stutter outstanding
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it's just too bad not every game is like this if Tomb Raider is the poster child
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Watch Dogs is the one in the corner with the duns hat scaling from one GPU to two
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seems okay at first glance if we only look at average frame rates but minimum
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frame rates tell a bit more of the story they dropped almost in half and this
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hitching and stuttering was very noticeable in game it actually gets
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worse the more graphics cards you add yet another issue for the PC version of
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Watchdog next up is Far Cry 3 something
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unusual you might notice about this game is that the minimum frame rates are very
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close to the average frame rates in some cases this is because our run for this
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game involves driving around a track running over dudes and getting shot at
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and looks very consistent having minimum and average frame rates close to each
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other makes animations appear very smooth on screen at least with one or
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two gpus installed in the system even though average frame rates scale very
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well with more gpus you can see that minimums don't and this manifests as
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uneven inconsistent movement of objects on screen with three or four graphics
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cards our last game is Crisis 3 just
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like Far Cry 3 it scaled well from 1 to 2 gpus but we see the same issue with
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great average frame rate scaling and poor minimum frame rate scaling that
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translates to uneven lurchy animations in the case of Crisis 3 it was actually
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noticeably worse than Far Cry 3 with three-way and four-way SL so much so
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that as a gamer I would much rather play with two graphics cards at lower detail
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settings than with more graphics cards and game settings cranked speaking of
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in-game settings if you want to see how I was running everything check out the
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download link in the video description GPU boost clock speed was another
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interesting part of the story with two gpus we saw slightly lower turbo speeds
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because we hit our thermal limit sooner on the top card than the bottom one
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because it has less access to Fresh Air surprisingly though we reached the same
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GPU speed even in the other configurations pretty impressive when
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they're all packed in like sardines in a four-way config speaking of impressive
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power consumption I mean I mentioned before I threw A500 watt 80 plus
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titanium PSU in this rig to ensure that
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I wouldn't be limited the fan on it barely even turned on our four-way SLI
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configuration Drew 620 Watts from the wall in our stare at the fire test in
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Far Cry 3 that means that even accounting for another 50% capacity for
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future expansion 1,000 watt power supply would have been plenty for this rig so
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it's back on the bench all right now back up a second line is you run in here
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throw a bunch of graphs in our faces for five minutes and then basically voice
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over telling us to ignore the performance numbers because they don't reflect the gameplay experience what
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gives great question normally when we do
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benchmarks on this channel it's okay to use fraps to take average frame rates
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and compare graphics cards relative performance because in our game
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showdowns and our graphics card reviews we only test single GPU configurations
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with multi-GPU configurations particularly Beyond 2-way as I've been
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discussing in this video different measurements need to be taken
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to evaluate the evenness of the pace
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with which new frames are delivered to the gamer here's an example the video
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you're watching right now is playing at 30 frames per second
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smooth hold on a second what was that we only dropped the frame rate 3% to 29
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frames per second but because we're doing this by dramatically increasing
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the delivery time of just a few frames periodically you're seeing very
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noticeable hitches and stutters aren't you that's what I'm talking about now
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unfortunately we don't have the equipment to objectively measure the
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perceived smoothness of a game like you'll see on some of the hardcore Tech
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sites like PC per and tech report I recommend reading up on those sites by
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the way uh search for frame pacing if you want to learn more about this but
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the good news is that in the case of our multi-way SLI video today at least with
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this new and relatively immature driver for the GTX 980 it was easy to pick up
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on this stuff with the naked eye so being able to measure it wouldn't have
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changed the conclusion much and here it is what we've been saying for years is
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still true one of the fastest GPU you
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can afford is best in most cases because you'll always get the performance you
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paid for even in Watchdogs until you get
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up to the top tier cards at which point two of them might make sense if you
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really are hungry for more performance but beyond that things really come off
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the rails in a hurry and I guess I can see why NVIDIA offers you the capability
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to run more cards if they want to but didn't even have any three-way or
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four-way configs running even in their own demo systems at the gtx980 launch
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event so that pretty much wraps it up guys like this video if you liked it
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