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GLAMOR Radeon Shows 2D Acceleration Promise

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  • #46
    There's lots of room left for optimizations, they have just started to support this new acceleration path.

    However, this is what Chris Wilson said about Glamor (some statements refer to the intel driver) in another thread.

    Originally posted by ickle View Post
    There is a significant impedance mismatch between X and GL, that is tricky to overcome and adds lots of extra complexity, and with the extra abstraction layer you cannot exploit hardware features not exposed through a GL extension. Also you need to leak many details through that abstraction layer in order to allocate shared objects between multiple clients and your acceleration routines (which is quite, quite scary and hairy.) And there is the tiny issue of having a critcal system process relying on several hundred thousand lines of code that has not been written with robustness in mind, and having no failsafe method.

    With regards to performance, the current bottlenecks I see in glamor are due to the CPU overhead of the Intel mesa stack, and the many assumptions that interact extremely poorly with the 2D workload of glamor. Where you do find yourself mostly GPU bound (such as the fish-demo), glamor still falls short by 10-30% due to inefficiences in the GPU programming (too many state changes and poor optimisation of shaders) and the multiple abstraction layers. However, being GPU bound is the exception and typically you end up being ratelimited by one of the paths that are orders of magnitude slower. And then there is the issue that glamor is an absolute resource hog, as the intel mesa driver's buffer management has never been used like that before...

    In a perfect world, glamor would equal the performance of a highly specialised driver like SNA; much of the routines used in SNA can be mapped directly onto the OpenGL API - and most have been copied over to glamor. Lots of work needs to be done to tune the entire mesa stack, a lot of which I suspect will only benefit glamor.

    And remember, RENDER acceleration is just one small part of the driver.

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    • #47
      Yep, unfortunately every option (including starting a new DDX architecture or continuing the existing EXA-based DDX) have real, well known challenges. That's what makes picking one so much fun

      I think it's fair to say that any of the options will need work to get to a "happy place" -- the issue was that glamor seemed to offer the best combination of good return on short term work and not too many architectural obstacles for the longer term.

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      • #48
        Originally posted by ChrisXY View Post
        So now that it works with xorg-git I tested it. HD 6550M.

        Code:
        ~ % grep -i glamor /var/log/Xorg.0.log
        [   295.584] (II) LoadModule: "glamoregl"
        [   295.584] (II) Loading /usr/lib/xorg/modules/libglamoregl.so
        [   295.587] (II) Module glamoregl: vendor="X.Org Foundation"
        [   295.597] (**) RADEON(0): Option "AccelMethod" "glamor"
        [   295.597] (II) Loading sub module "glamoregl"
        [   295.597] (II) LoadModule: "glamoregl"
        [   295.597] (II) Loading /usr/lib/xorg/modules/libglamoregl.so
        [   295.597] (II) Module glamoregl: vendor="X.Org Foundation"
        [   295.597] (II) glamor: OpenGL accelerated X.org driver based.
        [   295.608] (II) glamor: EGL version 1.4 (DRI2):
        [   295.633] (II) RADEON(0): glamor detected, initialising EGL layer.
        [   296.112] (II) RADEON(0): Use GLAMOR acceleration.
        GtkDrawingArea - Lines - time: 224,47
        GtkDrawingArea - Circles - time: 26,41
        GtkDrawingArea - Text - time: 0,80
        GtkDrawingArea - Pixbufs - time: 0,59
        ---
        Total time: 255,36[/code]

        Even when completely done in software: 224 seconds for the line drawing? Is there something wrong or is this just the way it is for now?


        ---
        Total time: 9,05[/code]
        The draw lines haven't been fully optimzied yet, glamor has been focusing on the compositing/rendering part so far.
        For example drawing non vertical/horizontal lines fallback to software rendering which is very very slow, so it took
        224 seconds at your benchmark. But that is not difficult to accelerate, just need a simple shader to do that.

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        • #49
          Originally posted by gongzg View Post
          The draw lines haven't been fully optimzied yet, glamor has been focusing on the compositing/rendering part so far.
          kwin with opengl effects did indeed work quite well already.

          Originally posted by gongzg View Post
          For example drawing non vertical/horizontal lines fallback to software rendering which is very very slow, so it took
          224 seconds at your benchmark. But that is not difficult to accelerate, just need a simple shader to do that.
          Good to know, thanks.

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