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Björne2's avatar
Björne2
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12 months ago

Intel OpenCL compiler (aoc) does not coalesce global memory reads anymore

The two screenshots says it all. The old screenshot is generated with aoc 21.2.0. Note how it coalesces the 16 float reads into one 512 bit DDR read. The new screenshot is generated with aoc 2024.2.1. It does not coalesce the 16 float reads and instead creates 16 individual read ports. Afaict, that is quite bad for performance and it wastes a lot of hardware resources.

Is there a way to make aoc 2024.2.1 coalesce, exactly like the old compiler did?

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8 Replies

  • Björne2's avatar
    Björne2
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    11 months ago

    Hi BoonBengT and yuguen. I know that OneAPI only support SYCL. But SYCL is horrible for FPGA work so I'm sticking with OpenCL. Besides, SYCL is just a thin layer on top of OpenCL anyway. I solved my issue by removing the "volatile" keyword. Apparently, in recent versions volatile prevents memory coalescing.

    • yuguen's avatar
      yuguen
      Icon for Occasional Contributor rankOccasional Contributor
      11 months ago

      There is no guarantee that anything coming out of aoc will be functional as this tool is now deprecated.

      What are your complaints about SYCL compared to OpenCL?

      • Björne2's avatar
        Björne2
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        11 months ago

        I know that, but the replacement SYCL tools are that bad. The main problem is that icpx embeds the FPGA image into the host code so you can't have one binary that switches between multiple images via command line parameters. Nor one binary with kernels for multiple different devices. icpx also takes 10 seconds for simple examples which compile instantly in OpenCL. It wouldn't be so bad if you could use a regular C++ compiler for the host code and just use icpx for the device code, but I haven't found any (easy) way of accomplishing that.

  • BoonBengT_Altera's avatar
    BoonBengT_Altera
    Icon for Moderator rankModerator
    11 months ago

    Hi @Björne2,


    Greetings, as we do not receive any further clarification/updates on the matter, hence would assume challenge are overcome. Please login to ‘https://supporttickets.intel.com’, view details of the desire request, and post a feed/response within the next 15 days to allow me to continue to support you. After 15 days, this thread will be transitioned to community support. For new queries, please feel free to open a new thread and we will be right with you. Pleasure having you here.


    Best Wishes

    BB


  • BoonBengT_Altera's avatar
    BoonBengT_Altera
    Icon for Moderator rankModerator
    12 months ago

    Hi @Björne2,


    Greetings, just checking in to see if there is any further doubts in regards to this matter.

    Hope your doubts have been clarified.


    Best Wishes

    BB


  • BoonBengT_Altera's avatar
    BoonBengT_Altera
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    12 months ago

    Hi @Björne2,


    Good day, just following up on the previous clarification.

    By any chances did you managed to look into it?

    Hope to hear from you soon.


    Best Wishes

    BB


  • yuguen's avatar
    yuguen
    Icon for Occasional Contributor rankOccasional Contributor
    12 months ago

    The OpenCL SDK for Intel FPGAs is no longer distributed since 22.4.

    Therefore, 22.4 is the last version of the compiler to officially support OpenCL as an input language.

    How did you get a 2024.2.1 version of aoc? I'm guessing that you got that binary from a oneAPI SYCL compiler for FPGA install.

    The SYCL compiler uses aoc internally, but is not expected to work as a standalone.