External GPU on nMP?

Discussion in 'Mac Pro' started by abluehaze, Jan 5, 2014.

  1. abluehaze, Jan 5, 2014
    Last edited: Jan 5, 2014

    abluehaze macrumors regular

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    #1
    I've been browsing the forums trying to come to a decision on whether to buy a nMP for general use/gaming or top of the line iMac with 780m. I ran across a thread talking about connecting a external graphics card using Thunderbolt and I hadn't thought of that.

    Would it be possible to connect an external gaming GPU to the nMP to use while gaming in OSX and or Windows? Does anyone know how much it would cost to get an external Titan or better and if that's possible?

    Thanks in advance.
     
  2. jbg232 macrumors 65816

    jbg232

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    #2
    Because of the chipset architecture, the bandwidth across all the thunderbolt 2 ports maxes out at 1300 MB/sec. This kind of bandwidth is really not sufficient to run an external GPU capable of 4K resolution at 60hz. You can read more about these limitations in the excellent anandtech review here and here.
     
  3. abluehaze thread starter macrumors regular

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    #3
    Ok, what about a non 4K display, ie a 27 inch cinema display?
     
  4. jbg232 macrumors 65816

    jbg232

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    #4
    Even a non 4k display the bandwidth will still be pretty limiting. Although 1300mb seems like a lot, and for everything except video it is, an external gpu is still not a real possibility for most. You can search the forums and see what people have been doing.
     
  5. slughead, Jan 5, 2014
    Last edited: Jan 5, 2014

    slughead macrumors 68040

    slughead

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    #6
    Whewwww 1300... that's rough.

    That's almost PCIE 1.0 4x -- now to dig up that article about running GPU over low speed slots..

    2.0 4x (2GBps) was pretty bad but alright with today's mid-range cards, if it really is closer to 1.0 4x (1GBps), that'll be a huge performance hit. You'd definitely be better off with the D700 in either case.

    Edit: found it: ~20-30% performance hit for 2012's best cards. The 780Ti/titan/690/7990/R9 290 will be hit much harder--not even worth the effort.

    Where external GPUs over TB2 will help is for extra openCL processing (if programs can use more than 2GPU).
     
  6. abluehaze thread starter macrumors regular

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    #7
    So basically it's not feasible at all. Not sure why it's been alluded then by the tech community that it's a possibility. No one in their right mind is going to want to spend hundreds of dollars to take a 20 percent performance hit. Thunderbolt obviously isn't where it needs to be yet.
     
  7. ActionableMango macrumors 604

    ActionableMango

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    #8
    For years now this has been a problem with external video cards.

    But it IS feasible. People bother to do this on older computers because desktop video cards are so much faster now that even with a 20% hit, they are still much faster than the older onboard mobile chips.

    Theoretically some day this will be true for the nMP as well. Although I suspect it will make more sense to drop in newer Apple GPU boards.
     
  8. EpicBlob, Jan 6, 2014
    Last edited: Jan 6, 2014

    EpicBlob macrumors member

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    #9
    PCIe 2.0 x4 is around an 12% loss, not 20-30% for a 680. an 8 percent loss is 88 fps instead of 100.

    I have my Mac Mini plugged into a ViDock eternal GPU with a nVidia 660, with PCI-e 2.0 x1. Just because it's 1/16th of the bandwidth doesn't mean that is even close to being relative to performance. I can play BF3 on ultra 1080p at 46fps.

    2.0 x4 is plenty, trust me on that. And don't forget you'll probably be plugging in a nVidia gaming GPU, so that will by itself beat out the WORKSTATION cards inside the nMP.

    ----------

    No one would buy one for their new system. I had a 2012 Mac Mini, but wasn't going to buy an entirely new computer for gaming. I can now play any game I want with my external 660 gpu. In bf4, I got an avg. of 44fps on medium, 1080p on a 64man multiplayer sever. Not too shabby for a Mac Mini.
     
  9. Killerbob macrumors 6502a

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    #10
    So basically, with an external GTX680 you'd not experience the incredibly slow gaming performance of a pair of D500s or D700s? You would have a 10-20% hit?

    I am asking because I will not have two machines sitting on my desk! I use my MP for photo and video editing plus typical productivity stuff, as well as the occasional gaming, and if I switch out my trusty MP3,1/2.8GHz Octo/16GB/Accelsior PCIe/GTX680 with an MP6,1/3.5GHz Hex/32GB/PCIe Storage/D700, I will want to make sure I am not hit by a gaming decrease of 50%!

    The 50% is the Heaven Extreme benchmark score difference between my MP3,1/GTX680 and the nMP/D500... (the GTX680 being faster)
     
  10. leman macrumors 604

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    #11
    The duo of D700s is performing quite close to the Titan anyway - why woukd you need an external GPU in the first place?
     
  11. Killerbob macrumors 6502a

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    #12
    I haven't seen a Heaven benchmark on the D700s, but the D500s are significantly slower than a single GTX680 in gaming at least.
     
  12. slughead, Jan 6, 2014
    Last edited: Jan 7, 2014

    slughead macrumors 68040

    slughead

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    #13
    The D700 does quite well in games with XFire under Windows.

    So I was referring to the Anandtech article which said they could only get 1.3GBps out of the thunderbolt 2 port in the nMP.

    If this is true for GPUs as well (as I suspect it will be), then you should look at PCie 1.0 4x NOT 2.0.

    So 4 things wrong with this:

    1) Workstation cards like the W9000 work just fine in games--almost identical to the 7970GE in gaming performance.
    2) The D700 Probably is more like a rebranded Consumer card
    3) The D700 is already performing about as well as a 12-20% underclocked 280X (7970GE) -- not bad. In Xfire, it's about as good as a GTX780
    4) Given 3 (which is a fact proven by benchmarks), any card that would get better performance such as a 7990/GTX690/GTX780/GTX780Ti/Titan/R9 290 would probably be neutered by having PCIe 2.0 4X

    The only numbers we have are for the 680 and previous, the newer cards, as they are faster, will be further neutered.

    To summarize: if Anand's test is accurate and we're talking more like 1.3GBps, this is a 20-30% loss in midrange cards of today (GTX680, for instance). Even at PCIe 2.0 4x, any card you'd actually want to replace the D700 with would have a huge performance hit.
     
  13. abluehaze thread starter macrumors regular

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    #14
    The performance in windows is acceptable with the d700s because of Crossfire.

    The issue is under osx. Most sites and reviews are stating that the d700 is only matching the performance put out by the 780m in the top of the line iMac which is pretty pathetic.

    A top of the line workstation card is only able to keep up with a mid grade mobile gpu?

    I don't consider that very good performance.
     
  14. EpicBlob macrumors member

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    #15
    Yes, I agree that a D700 probably wouldn't need an external GPU. For anyone who plans on buying that setup, then disregard this article. But for the other cards (more so the lower end model) an external GPU would be a smart move to turn a single system into both a workstation and gaming PC. And trust me, it scales. A 680 on that bandwidth doesn't mean the total bandwidth has capped your performance; buying a 780 would still net you a performance increase. I've upgraded from a 560 to and 660 (soon to be 670) with my setup at 2.0 x1 and I've seen a steady increase so far (many tests online show a 670 will net me an increase with the 670 as well).

    I think it is very fair to say that an external GPU for a nMP would make a whole lot of sense for people with models other than the top end.

    ----------

    Yeah, this is where external cards will benefit. Gaming in OS X will be much better with an external nvidia GPU. But lets be honest, OS X isn't exactly known for playing games lol.
     
  15. slughead, Jan 7, 2014
    Last edited: Jan 7, 2014

    slughead macrumors 68040

    slughead

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    #16
    I hadn't seen OS X gaming benchmarks. That sounds like a nightmare.

    A couple of things: First, I didn't know you could run a Thunderbolt GPU in OS X, I thought all the setups were in windows. Second, in general Windows is going to be ridiculously better for gaming. If you're hell-bent on gaming in OS X, that does change things as the drivers are so G_d awful even great cards run poorly. Third, since the nMP doesn't have a CPU with GPU on it, you'd have to plug your monitor into the external card.

    If the D700 is being stomped by the 780M, my guess would be it's a driver issue (which may get corrected).

    I agree with EpicBlob then: With the qualifier being that one must game in OS X and that you're not using the D700, it's possible you can get better performance with an external GPU. My guess is it wont be a huge boost, but it'll be a boost.
     
  16. Killerbob macrumors 6502a

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    #17
    I do not think that many peole (if any) does gaming in OSX. I for sure do not, and what I want to do is use OSX for all my serious work, and bootcamped Windows for gaming. Hence, when I am in Windows the D700s will work in Crossfire.

    I can appreciate that my current GTX680 is a gaming videocard, which performs really well. Especially against a workstation videocard like the D500/D700. However, I was expecting more, and I will need to look for graphics alternatives if the D700 combo does not perform better than what I have seen thus far, albeit that being benchmarks based on graphics performance in OSX.

    Anyone have any graphics benchmarks from the nMP running Windows, using a pair of D700s?
     
  17. AndyUnderscoreR macrumors regular

    AndyUnderscoreR

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    #18
    That's because there were so few people attaching high end cards to their Macs that it wasn't worth games companies and video card makers sorting out decent drivers for all the different options, or bothering supporting the few Mac gamers with dual GPU setups,

    The new Mac Pro changes all that.

    To support the new Mac Pro, game developers no longer have to work with a million and one different cards and a range of third party drivers, and divide their dev time between catering for dual and single GPUs configurations from a range of different manufacturers, and covering a range of proprietary technologies like CUDA. Now they just need to work with 3 quite similar cards, all from AMD, use just one consistent set of Apple drivers, and they can safely assume everyone will have dual GPUs.

    When every reviewer is going to be testing how fast their games perform on dual D700s, Mac games developers are going to make damn sure their games run well on Dual D700s. They will care a lot less than before about supporting anything unusual like external GPUs on a low bandwidth connection. External cards *might* boost older games that were written to support anything but optimised for nothing, but for anything written from this year onwards, you can expect games to be heavily optimised for dual D300/500/700s and weak on supporting anything else.
     
  18. Cubemmal macrumors 6502a

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    #19
    I wouldn't be sure about that. There will be very few D700's in the wild comparatively, and few of those interested in games. As a game developer I'd be unlikely to invest much time optimizing for such a small user base.

    As Mac gaming is small I'd be unlikely to optimize at all. If I did I'd shoot for the iMac for the most part.
     
  19. Wardenski macrumors 6502

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    #20
    I disagree. On steam, only 1-2 % of Mac machines are (old) Mac Pros and these use what are essentially PC cards. Its not worth the effort of the developers.
     
  20. leman macrumors 604

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    #21
    Well, there is no crossfire support for OS X (and probably won't be any soon). Game developers are welcome to roll their own CF implementation (isn't that difficult for most games). And the OS X performance is further hindered by suboptimal mac graphics drivers.

    That said, there are probably not many games under OS X which require a beefy GPU. Most demanding games are Windows only, where performance is less of a problem.

    780M is far from being a mid grade module GPU - its the fastest one to date.


    Specific support for the new Mac Pro is a waste of development effort. You can't make a living selling games to nMP users - there are simply not enough. If I were to write a game for OS X (well, I actually am :D ), I would spend most of my optimisation effort for Intel iGPUs - because that will be the GPU most of my customers will be using.
     
  21. haravikk, Jan 7, 2014
    Last edited: Jan 7, 2014

    haravikk macrumors 65816

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    #22
    Not for gaming no; I think the main benefit of an external GPU will really be for adding additional compute power for OpenCL, provided your data set isn't so huge you'll run out of bandwidth of course.

    Otherwise it seems mostly of interest to lower powered devices like laptops or maybe a Mac Mini, but even so more modern integrated GPUs should still be far superior overall, as they become available (take a look at the Iris graphics in the new Macbook Pros).
     
  22. fhenry macrumors regular

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    #23
  23. EpicBlob macrumors member

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    #24
    My Mac Mini went from playing Battlefield 3 at 4fps to 46 fps. Tell me that "the integrated GPUs they use should still be far superior overall". And I'm using a midrange 660 gpu and pcie 2.0 x1.
     
  24. haravikk macrumors 65816

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    #25
    Sorry, I really mean newer integrated GPUs, you're right that the ones on the current Mac Minis are horrible, I keep forgetting they're not on Iris graphics yet, here's hoping they're updated soon!
     

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