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Thread: dGPU (7670M) in Muxless Dual Graphics Laptop Is Worse Than The iGPU (7660G)?

  1. #1
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    Default dGPU (7670M) in Muxless Dual Graphics Laptop Is Worse Than The iGPU (7660G)?

    I have a Acer Aspire V3-551G-X419 laptop which has a 7660G (on the APU; iirc it's a A10-4600M) + a 7670M dedicated chip for graphics. This laptop is also muxless.

    I'm running Xubuntu 14.04 with 3.14.0-999-lowlatency (yesterday's daily kernel from PPA), and oibaf's PPA. I have radeon.dpm enabled, and have also done the setprovideroffloadsink thing for Prime (on auto-start). SwapBuffersWait is disabled, and vblank_mode is 0. I use DRI_PRIME= 0 and 1 to specify the GPU to use.

    On all the benchmarks I've done (TF2, CSS, Dota 2 timedemos and GtkPerf), the 7670M dGPU seems to score slightly lower than the 7660G iGPU. There isn't a significant difference in most cases, but I would expect the 7670M to perform far better than a 7660G. I also noticed significant tearing with a game in Wine (osu!) also on the dGPU.

    I'm wondering if this is expected behaviour currently just given the state of the open-source drivers, or maybe there's some setting somewhere I may of overlooked? Also for a slightly unrelated question, is there anyway to use the dGPU without having compositing enabled?

  2. #2
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    Quote Originally Posted by Espionage724 View Post
    I have a Acer Aspire V3-551G-X419 laptop which has a 7660G (on the APU; iirc it's a A10-4600M) + a 7670M dedicated chip for graphics. This laptop is also muxless.

    I'm running Xubuntu 14.04 with 3.14.0-999-lowlatency (yesterday's daily kernel from PPA), and oibaf's PPA. I have radeon.dpm enabled, and have also done the setprovideroffloadsink thing for Prime (on auto-start). SwapBuffersWait is disabled, and vblank_mode is 0. I use DRI_PRIME= 0 and 1 to specify the GPU to use.

    On all the benchmarks I've done (TF2, CSS, Dota 2 timedemos and GtkPerf), the 7670M dGPU seems to score slightly lower than the 7660G iGPU. There isn't a significant difference in most cases, but I would expect the 7670M to perform far better than a 7660G. I also noticed significant tearing with a game in Wine (osu!) also on the dGPU.

    I'm wondering if this is expected behaviour currently just given the state of the open-source drivers, or maybe there's some setting somewhere I may of overlooked?
    Did you enable HyperZ ? R600_DEBUG=hyperz. I don't really know about the performance of both cards, but notebookcheck ( http://www.notebookcheck.net/AMD-Rad...s.81173.0.html ) says they are relatively on the same level, being the 7660g a bit slower. What type of memory does your dGPU have?

    Quote Originally Posted by Espionage724 View Post
    Also for a slightly unrelated question, is there anyway to use the dGPU without having compositing enabled?
    I remember asking Dave Airlie about this some months ago, and he said "not yet", so I guess we'll either have to wait until some hacker makes it possible, or just wait for wayland/Xorg 1.16, since (AFAIK) they improve many things regarding compositors ..
    Also, it would be very cool to have crossfire in these systems

  3. #3
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    Yeah, the two GPUs aren't that far apart -- I think they were picked to be compatible-ish for Crossfire use, not for a "big dGPU / small iGPU" arrangement. The 7670M seems to be a 5-way VLIW part with 480 SPs, while the 7660 in the Trinity is a 4-way VLIW with 384 SPs, so basically same number of SIMDs just 4-way rather than 5-way.

    Engine clocks & memory bandwidth are lower on the integrated GPU, but I guess there's more overhead getting to the dGPU so maybe they balance out.

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    You need to use a compositor since the dGPU is not connected to any displays (muxless). No one has any plans to support non-composited scenarios. Additionally, the 7670M comes in two forms, one with ddr3 memory (which is comparable to system memory) and gddr5 which is much faster. Finally, there is no inter-device synchronization mechanism for shared buffers yet (one is in progress) so buffer synchronization hurts performance a lot currently.

  5. #5

    Unhappy Crossfire

    Quote Originally Posted by asdfblah View Post
    Also, it would be very cool to have crossfire in these systems
    *sigh*

  6. #6
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    Ah, thanks for the clarification everyone. Looks like I may as well just keep the dGPU powered off for now (if possible; I recall seeing some commands somewhere) and stick with the iGPU.

    Quote Originally Posted by asdfblah View Post
    What type of memory does your dGPU have?
    Quote Originally Posted by agd5f View Post
    ... Additionally, the 7670M comes in two forms, one with ddr3 memory (which is comparable to system memory) and gddr5 which is much faster.
    I have the DDR3 version of the 7670M.

  7. #7
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    Quote Originally Posted by agd5f View Post
    You need to use a compositor since the dGPU is not connected to any displays (muxless). No one has any plans to support non-composited scenarios. Additionally, the 7670M comes in two forms, one with ddr3 memory (which is comparable to system memory) and gddr5 which is much faster. Finally, there is no inter-device synchronization mechanism for shared buffers yet (one is in progress) so buffer synchronization hurts performance a lot currently.
    Thanks for explaining that.

    Quote Originally Posted by halfmanhalfamazing View Post
    *sigh*
    Alex has said before, it can be done, we just need someone to do it

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