970 memory allocation issue revisited

Discussion in 'Videocards - NVIDIA GeForce' started by alanm, Jan 23, 2015.

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  1. Anarion

    Anarion Ancient Guru

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    It's not always possible to fill exactly 4096 MB for obvious reasons, you should know that. The game might want to use more than that 39 MB but because it can't fit that data it just can't completely max it out. I any case we are talking about 39 megabytes here - that's absolutely nothing.

    It will use that 3,5GB pool first...
     
    Last edited: Jan 25, 2015
  2. Extraordinary

    Extraordinary Ancient Guru

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    I had to change mine to 4GB, not sure if it auto changes once you go past the default
     
  3. da_unique

    da_unique Member Guru

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    Sadly the benchmark seems to only work for 9xx series, getting this on my gtx670:
    http://i.imgur.com/FZLeRlD.jpg
    lol
    So far the accuracy of the bench :X
     
  4. rflair

    rflair Don Commisso Staff Member

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  5. Hilbert Hagedoorn

    Hilbert Hagedoorn Don Vito Corleone Staff Member

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    RTSS output will show you the total Vmemory used. You can change the upper limit for the graph plotting in properties btw.

    On a generic notice, I've been using and comparing games with both a 970 and 980 today, and quite honestly I can not really reproduce stutters or weird issues other then the normal stuff once you run out of graphics memory.

    Once you run out of ~3.5 GB memory or on the ~4GB GTX 980 slowdowns or weird behavior can occur, but that goes with any graphics card that runs out of video memory.

    I've seen 4GB graphics usage with COD, 3.6 GB with Shadows of Mordor with wide varying settings, and simply can not reproduce significant enough anomalies. Once you really run out of graphics memory, perhaps flick down the AA mode a tiny bit from 8x to 4x or something.

    The 3.5 GB partition on the GTX 970 is a big miss from Nvidia, but mostly for not honestly communicating this. The problem I find to be more of a marketing miss with a lot of aftermath due to not mentioning it.

    Would Nvidia have disclosed the information alongside the launch, then you guys would/could have made a more informed decision. For most of you the primary 3.5 GB graphics memory will be more than plenty in 1080P and 1440P.
     
  6. sykozis

    sykozis Ancient Guru

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    You should see it run on a GTX590....lol. According to that "benchmark" the GTX590 has ExoBytes of memory bandwidth.

    Thank you for responding to this Hilbert.
     
    Last edited: Jan 25, 2015
  7. iTile

    iTile Member

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    I called it.. LOL
     
  8. 4KOLED

    4KOLED Member

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    sorry i dont wanna read the 28 pages, but did you notice the same issue with 980 ?

    cause someone does...
     
  9. sykozis

    sykozis Ancient Guru

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    It's actually a drawback of the architecture and how NVidia chose to design/implement the memory controller. When they "cut-down" the GPU, it loses memory bandwidth and a portion of the memory will become "slower" as a result. The memory bus is in fact 256bit. The memory controller simply isn't able to use the full bandwidth on a small portion of the memory due to SMM's being disabled.
     
  10. Monchis

    Monchis Maha Guru

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    Maybe they could make a test driver that uses those 500mb as first resource to calm the paranoia?. :)

    Or maybe be more clear in their specs next time around?.
     
    Last edited: Jan 25, 2015

  11. sykozis

    sykozis Ancient Guru

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    Exactly what "issue" are you referring to?
     
  12. 4KOLED

    4KOLED Member

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    the same story about vram slowing down from reaching ~ 3.5 GB vram
     
  13. sykozis

    sykozis Ancient Guru

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    The GTX460 768mb cards had the same behavior. They'd fill the first 512mb of VRAM and wouldn't touch the last 256mb unless absolutely necessary because it was slower. They used a 128+64bit implementation to get the "192bit" memory bus on those cards. Nobody made a huge fuss over it either....

    Read post #690 from Hilbert Hagedoorn. It's explained there.
     
  14. Monchis

    Monchis Maha Guru

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    I know of a couple of forums where they made huge fuss about the gtx660.
     
  15. sykozis

    sykozis Ancient Guru

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    Similar design there to the GTX460 768mb cards. In the defense of the GTX660 though, it was crap to begin with. Most of just upgraded from cards slow enough to make the 660 look better than it really was. In my case, it was 10-50% slower than the 560Ti I replaced in most instances.
     

  16. 4KOLED

    4KOLED Member

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    Hilbert says over 4Gb for the 980, but i found a 980 which has a slowed down bandwith from 3.5 GB, is the first or u already knew it ?
     
  17. Fox2232

    Fox2232 Ancient Guru

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    Sure. But it leaves quite some uncertainty, since utilization was at max for only 2 points and rest was quite below.

    But to add actual value, since only one person went to create my synthetic scenario to see possible impact (not regular one), I'll show some math.

    GTX970 has official memory bandwidth of 224GB/s.
    Nai's Bench shows 150GB/s for fast part & from 6 to 22GB/s for slow part. Normalizing this to:
    224GB/s for fast & 21GB/s for slow address space.
    Scenario 1: Big game uses 3.2GB, but per frame uses only 768MB (0.75GB)
    - best case scenario: 0.75 / 224 = 0.00335 ~ max achievable fps = 298.67
    - worst case scenario: 0.5 / 21 + 0.25 / 224 = 0.0249 ~ max achievable fps = 40.12
    - Average scenario: 0.09375 / 21 + 0.65625 / 224 = 0.0074 ~ max achievable fps = 135

    Scenario 2: very small game utilizing 0.75GB, but per frame using exactly 0.5GB (small arena game)
    - best case: 0.5 / 224 = 0.002232 ~ max fps = 448
    - worst case: 0.5 / 21 = 0.02381 ~ max fps = 42
    - average case: 0.0625 / 21 + 0.4375 / 224 = 0.004929 ~ max fps = 203

    Explanation for average case:
    Since only 0.5GB out of 4 is slow, we have (if random distribution applies) 12.5% change to put data into slow region.

    And as you can see, since performance of games which utilize on their own 3.5GB of vram is already in range of 25 to 45 fps, impact of this slow part is minimal.

    I believe nVidia did best thing they could by separating address spaces this way. Because otherwise there would be cases where perfectly fine running games end up with huge framerate drops. Imagine going from 120 to 40fps with no apparent visual effects going on screen, just by entering room full of slow textures.
     
  18. rflair

    rflair Don Commisso Staff Member

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    The first paragraph makes no sense at all.

    The second is naturally how the chip is configured. The GTX980 is a full GK204 configuration, the GTX 970 will never be better.

    The last part makes no sense, it is a 256bit card, look at the chip layout. The thing is Nvidia ties the SMM/Cuda cores to be allocated a certain amount of memory each, this is where the memory segmentation happens. The thing that has me wondering is how the segmented memory is used; is it one large block of memory, or little packets?
     
  19. alanm

    alanm Ancient Guru

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    Someone elsewhere posted this on what may be going on, that the card can "load 4GB but only 3.5 can be sent to the SMMs, the data in the remaining 0.5GB cant be sent for execution to the SMMs used for executing the datas that are within the 3.5GB, it s only a theory but the GPU design and the presence of a separated partition point to this implementation, what transpire is that each SMM has a fixed adress space in the RAM and that data meant to be executed by a given SMM must be retired in the relevant adress space, if this given SMM is disabled there s no mean to send the data to another SMM, so as said the whole 4GB is adressable but only 3.5GB can be executed by the GPU computing units..."

    Which in effect may indeed make it a 3.5gb card. Although I still dont believe that is the cause of crippled performance in examples others have presented here and elsewhere.
     
  20. alanm

    alanm Ancient Guru

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    It may have, but its probably due to very highly set settings that can slow things down regardless of vram usage.
     
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