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GTX980 PCIe bandwidth scaling inc x4 1.1 (~TB1) and x4 2.0 (TB2)

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Here is a very interessting review about the PCIe bandwidth scaling with a GTX 980. You can see how some games can even improve from x16 2.0 to x16 3.0 (BF4) and some don't care all the way "down" to x4 2.0 (Tomb Raider).

GeForce GTX 980 PCI-Express Scaling - Performance Summary

Real performance losses only become apparent in x8 1.1 and x4 2.0, where the performance drop becomes noticeable with around 15%.

I think that is what most eGPU Thunderbolt 2 users can confirm / expect while using a 15" MBPr with i7.

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Wow, that's interesting! That means that generally, the performance hit for a TB2 eGPU is in the region of 2% for 4K. That is almost nothing. But then again, single cards aren't really known to be excellent for 4K gaming (they can do 30+ FPS in most games, but not the 60 FPS every PC gamer wants)!

Can't wait until I upgrade my 780 Ti now!

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Cumulative graphs are handy but game-specific graphs tell a different story.

Look at games like Ryse, even at 1080p the performance hit is dramatic.

Even with TB2 and the full 4x pcie2.0 lanes (16Gbps), you get 45fps at 1080p. With a gtx980.

There must be some technical reason behind it, but there are definitely some games that benefit from every Mbps of bandwidth you throw at them. So always go with TB2 if possible. And cross your fingers for TB3 (pcie3.0 4x) to become available as soon as possible.

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Remember that those tests were done with highest quality settings (custom), and they are not comparable to my just updated 4K results. I used default high/ultra/ultimate in Tomb Raider and default medium/high/ultra in BF4:

http://forum.techinferno.com/implementation-guides/7580-%5Bguide%5D-2014-15-macbook-pro-iris-gtx780%4016gbps-tb2-akitio-thunder2-win8-1-a.html#post103029

I did a few additional test in Tomb Raider to see how close TB2 is x4 speed in reality:

AKiTiO + GTX 780 OC 6GB (3840 x 2160, highest settings, NoAA, TressFX disabled):

29,1 (min)

42 (max)

34,7 (average)

AKiTiO + GTX 980 4GB reference card (3840 x 2160, highest settings, NoAA, TressFX disabled):

30 (min)

42,7 (max)

36,4 (average)

AKiTiO + GTX 980 4GB reference card (1920 x 1080, highest settings, 4xAA TressFX disabled):

44,6 (min)

78 (max)

60,7 (average)

All the tests done with a Samsung UHD 28" Monitor + DisplayPort cable. GTX 780 OC 6GB is very close to GTX 980 4GB at higher resolutions. The other conclusion is that TB2 is slower than x4 1.1 in Tomb Raider when we look at the average FPS values, but we have to take into account that 2014 MBPr 15" is not a desktop computer. However, it performs very well when playing with default quality settings, and with the newest 344.65 driver, you will get a few more FPS.

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Check out the bandwidth performance hit when trying different PCIe speeds with a 7970 from anadtech.

Thanks. Keep in mind that TB2 will offer PCIe 2.0 x4 performance, which is equal to PCIe 3.0 x2 (used in the anadtech benchmarks).

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I had no idea how much variation there was between games. I wonder what makes some games less dependent on the pcie bandwidth, i.e. Metro vs. Wolfenstein?

I've noticed performance improvements with my TB1 setup in GTAV when I changed the "Maximum pre-rendered frames" to 1 in the Nvidia control panel. Could this have something to do with bandwidth? I wonder if any of these performance drops can be improved at all with some settings tweaks..

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I had no idea how much variation there was between games. I wonder what makes some games less dependent on the pcie bandwidth, i.e. Metro vs. Wolfenstein?

I've noticed performance improvements with my TB1 setup in GTAV when I changed the "Maximum pre-rendered frames" to 1 in the Nvidia control panel. Could this have something to do with bandwidth? I wonder if any of these performance drops can be improved at all with some settings tweaks..

The current Wolfenstein games rely on the id Tech 5 engine which streams textures constantly as far as I've understood. That's the reason why there are texture pop-ins especially in games using this engine. So there's a stream of textures loaded and removed from the memory(RAM, HDD) to the memory of the GPU which demands bandwidth.

Other games, especially those that have closed levels with loading screens on area change, may load the textures only once and then they're done until the next request(area change).

The games that profit of high bandwidth or demand it are less often, though. I only remember CoD being one of the series.

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The current Wolfenstein games rely on the id Tech 5 engine which streams textures constantly as far as I've understood. That's the reason why there are texture pop-ins especially in games using this engine. So there's a stream of textures loaded and removed from the memory(RAM, HDD) to the memory of the GPU which demands bandwidth.

Other games, especially those that have closed levels with loading screens on area change, may load the textures only once and then they're done until the next request(area change).

The games that profit of high bandwidth or demand it are less often, though. I only remember CoD being one of the series.

Do you think "Maximum pre-rendered frames" setting would help this bandwidth demand in any way?

I wonder because I was having some frame hitches in GTAV and it helped me a lot when I set this value to '1'.

The way I understand it, the higher the setting on the pre-rendered frames, the more CPU intensive the graphics are. Would this, in turn, increase the demand for bandwidth?

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