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Radeon GCC Compute Back-End Approved For Merging In The Upcoming GCC9 Compiler

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  • Radeon GCC Compute Back-End Approved For Merging In The Upcoming GCC9 Compiler

    Phoronix: Radeon GCC Compute Back-End Approved For Merging In The Upcoming GCC9 Compiler

    As a follow-up to the story a few days ago about interest in getting the Radeon GCC compiler back-end merged for this year's GNU Compiler Collection 9 (GCC9) release, it's been approved!..

    http://www.phoronix.com/scan.php?pag...Merge-Approved

  • #2
    How does one use this? Does it call to the accelerator from within your CPU OpenMP loops?

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    • #3
      Originally posted by microcode View Post
      How does one use this? Does it call to the accelerator from within your CPU OpenMP loops?
      The GCC Offloading Wiki page - https://gcc.gnu.org/wiki/Offloading - though haven't looked yet to see if the AMD GCN back-end would follow the same approach or other limitations, etc.
      Michael Larabel
      http://www.michaellarabel.com/

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      • #4
        Now, someone just needs to port libc to it.

        BTW, this comes nearly in time for GCN to become obsolete!
        :-/

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        • #5
          Originally posted by coder View Post
          BTW, this comes nearly in time for GCN to become obsolete!
          :-/
          GCN obsolete? Do you know more than the rest of the world does?

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          • #6
            Originally posted by juno View Post
            GCN obsolete? Do you know more than the rest of the world does?
            I think the chip after Navi is supposed to be a fundamentally new architecture. Hopefully, it'll be the "Zen" equivalent of GPUs.

            https://www.anandtech.com/show/12233...nm-vega-on-7nm

            Granted, "Next-Gen" is awfully nebulous - could mean anything. I don't know whether I got the impression of a new ISA from any decent source, or maybe it was just speculation.

            It does seem like AMD is overdue for a new graphics architecture, however. Whether it's on the basis of perf/GFLOPS, perf/mm^2, or perf/Watt, AMD has been consistently outmatched by Nvidia since Maxwell. Also, consider that the first GCN products launched almost exactly 7 years ago.

            GCN has been quite a workhorse, but it's leaving too much performance on the table. Time for something new.

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            • #7
              Originally posted by coder View Post
              I think the chip after Navi is supposed to be a fundamentally new architecture. Hopefully, it'll be the "Zen" equivalent of GPUs.

              https://www.anandtech.com/show/12233...nm-vega-on-7nm

              Granted, "Next-Gen" is awfully nebulous - could mean anything. I don't know whether I got the impression of a new ISA from any decent source, or maybe it was just speculation.

              It does seem like AMD is overdue for a new graphics architecture, however. Whether it's on the basis of perf/GFLOPS, perf/mm^2, or perf/Watt, AMD has been consistently outmatched by Nvidia since Maxwell. Also, consider that the first GCN products launched almost exactly 7 years ago.

              GCN has been quite a workhorse, but it's leaving too much performance on the table. Time for something new.
              I guess it all depends on how much wizardry the AMD team can pull off.

              But I agree - GCN has been amazing, unless they can pull of some magic with Navi then I guess the next uArch is something we all have to wait for

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              • #8
                Originally posted by coder View Post
                I think the chip after Navi is supposed to be a fundamentally new architecture. Hopefully, it'll be the "Zen" equivalent of GPUs.

                https://www.anandtech.com/show/12233...nm-vega-on-7nm

                Granted, "Next-Gen" is awfully nebulous - could mean anything. I don't know whether I got the impression of a new ISA from any decent source, or maybe it was just speculation.
                I don't see any indication at all that the GPU after Navi won't be GCN.

                Every GPU that has no (public) name yet has been called "Next-Gen" at some point in time. E.g. Fiji. Is Fiji GCN?

                Originally posted by coder View Post
                It does seem like AMD is overdue for a new graphics architecture, however. Whether it's on the basis of perf/GFLOPS, perf/mm^2, or perf/Watt, AMD has been consistently outmatched by Nvidia since Maxwell. Also, consider that the first GCN products launched almost exactly 7 years ago.

                GCN has been quite a workhorse, but it's leaving too much performance on the table. Time for something new.
                GCN *is* basically the Zen equivalent of GPUs really. If it wasn't for the software (it's interesting to compare Chips from back then in today's workloads with today's drivers), they would've completely wiped the competition back then with the introduction of GCN. Remember the oh so "legendary" first GTX Titan? It's also always good to remember that Nvidia needed this monster chip to beat the 7970 by barely 20%, just to be beaten by Hawaii again. Of course, not everything was perfect. Hawaii shipped with crap coolers, destroying all the potential it had.
                Nobody demanded Nvidia to throw away everything they had and bring a completely new GPU architecture just because AMD had the lead back then. Admittedly, Nvidia's Marketing always did a compensation good job when their hardware wasn't great. Still, Maxwell, Pascal and Turing are all still based on Kepler. Even based on Fermi, FWIW.

                I also don't know where you get the impression from that AMD cards are inefficient by looking at perf/GFLOPS, perf/mm² and perf/Watt. First of all, "perf" is completely arbitrary. What are you talking about? Average games performance? Compute?

                What is true, is that Nvidia has a lead in gaming(!) perf/GFLOP since Maxwell. But that's not compute architecture related, it's mostly because of the new approach in rasterization, which is completely fixed-function. AMD could build a new rasterizer (which they tried with Vega) and it would still be GCN. Another big part is that Nvidia engineering seems to be very, very efficient with the fab process they are working with. They reach higher clocks with lower voltages and the overall chip quality variation isn't that large, which allows them to drive better default settings. So that's also not related to GCN.
                Looking closer at gaming performance, you also have to look at the consoles. It's impressive what those relatively weak boxes accomplish compared to AMD's (and Nvidia's) desktop PC GPUs. The difference is software, not hardware. That discrepancy between high theoretical hardware perf and low real gaming perf won't vanish by throwing away GCN.

                When it comes to perf/mm², perf/w in compute workloads, GCN is still very competitive, not least because Nvidia regressed in efficiency with Turing. BTW, Nvidia's CEO just confirmed that by being butthurt and acting like a crying 5 y/o boy.

                GCN came to stay and I expect it to stay for some while longer. I'm glad that software finally gets in shape, this GCC backend being one part of it.
                Last edited by juno; 01-13-2019, 06:05 AM.

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                • #9
                  Originally posted by juno View Post
                  I don't see any indication at all that the GPU after Navi won't be GCN.
                  Yeah, I don't know where I read that it's supposed to part from GCN.

                  Originally posted by juno View Post
                  GCN *is* basically the Zen equivalent of GPUs really.
                  I dunno. Maybe it's more like the GPU equivalent of Bulldozer. I mean, a barrel processor architecture in 2019? Really?

                  https://en.wikipedia.org/wiki/Barrel_processor

                  Originally posted by juno View Post
                  If it wasn't for the software ...
                  I'm not about to rehash this same old debate that's played out so many times, on so many forums.

                  Whether they can tweak GCN into something more efficient or do a ground-up redesign, I don't really care. They've got to do something to close the gap between where the specs say they should perform and what they actually deliver. And improve power efficiency.

                  Originally posted by juno View Post
                  (it's interesting to compare Chips from back then in today's workloads with today's drivers), they would've completely wiped the competition back then with the introduction of GCN. Remember the oh so "legendary" first GTX Titan? It's also always good to remember that Nvidia needed this monster chip to beat the 7970 by barely 20%, just to be beaten by Hawaii again. Of course, not everything was perfect. Hawaii shipped with crap coolers, destroying all the potential it had.
                  Thank you for making my point. GCN launched with a lot of potential, but it's been outpaced. I'd say ever since the lower-spec GTX 980 Ti stole Fury's thunder, AMD has fallen further and further behind.

                  And Hawaii was typical of the AMD brute-force approach. Too big and power hungry, with 512-bit memory bus and a huge die. Meanwhile, Nvidia was doubling down on efficiency, realizing that GPU performance is mostly a game of power efficiency.

                  Originally posted by juno View Post
                  Nvidia regressed in efficiency with Turing.
                  It seems to me they had exactly the same sorts of issues with 12 nm as the RX 590. Both were banking on the node shrink to buy more clock headroom, but it seems 12 nm under-delivered.

                  Originally posted by juno View Post
                  I'm glad that software finally gets in shape, this GCC backend being one part of it.
                  I'm all for it. I wish it happened sooner. I really do want AMD to succeed, but I don't let my desires or preference for openness cloud my view of reality.

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                  • #10
                    Hawaii was considerably *smaller* and more efficient than GK110. Neither is the typical GTX 980 Ti lower-spec to a typical Fury. If all your sources are this reliable, I'm sure GCN won't go anywhere.

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