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TimSweeneyEpic's profile
Tim Sweeney
Tim Sweeney
Tim Sweeney
@TimSweeneyEpic

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Tim Sweeney

@TimSweeneyEpic

Epic Games founder & CEO

epicgames.com
Joined August 2013

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    1. Tim Sweeney‏ @TimSweeneyEpic 29 Dec 2019
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      Tim Sweeney Retweeted Tim Sweeney

      This is up and running as a C++ library. Currently transactional variable reads and writes are ~50x slower than ordinary variables. 40% the overhead is transaction bookkeeping, 40% is concurrent garbage collection bookkeeping, 20% is platform atomics. Many optimizations to go.https://twitter.com/TimSweeneyEpic/status/1210260682605764611 …

      Tim Sweeney added,

      Tim Sweeney @TimSweeneyEpic
      Using the holidays for a 2-week coding session. Writing a new transactional memory manager that’s O(1) for all operations, completely non-blocking and progress-guaranteeing, and uses atomics only for writes.
      Show this thread
      19 replies 28 retweets 387 likes
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    2. Tim Sweeney‏ @TimSweeneyEpic 29 Dec 2019
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      This amount of overhead may be acceptable, as you'd only use transactional variables for shared globally-visible state (like properties of game objects) and not locals. If performance is dominated by low-level operations like collision detection, this may be negligible.

      2 replies 0 retweets 27 likes
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    3. Tim Sweeney‏ @TimSweeneyEpic 29 Dec 2019
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      For comparison, UE3 UnrealScript and pre-il2cpp Unity Mono bytecode interpretation were ~30x slower than native.

      4 replies 1 retweet 29 likes
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    4. Tim Sweeney‏ @TimSweeneyEpic 29 Dec 2019
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      One great side-effect of transactions is that you can automatically undo variable writes upon failure, for example so you can write something like "if(move a bunch of actors) ... else ...", and if any operations fail, then all of their effects are undone.

      1 reply 0 retweets 32 likes
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    5. Tim Sweeney‏ @TimSweeneyEpic 29 Dec 2019
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      I've had to re-learn my code optimization intuition from the late 90's. C++ compiler optimization is magic now, and Skylake can reliably issue 4-6 instructions per clock. But control flow misprediction has become wildly expensive.

      3 replies 4 retweets 61 likes
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      Tim Sweeney‏ @TimSweeneyEpic 29 Dec 2019
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      Anyway, there are two competing theories on how we'll unlock higher performance through parallelism. One is the data oriented design approach, asking programmers to rewrite gameplay code as highly parallel fragments of algorithms that pipe inputs and outputs among stages.

      11:02 PM - 29 Dec 2019
      • 61 Likes
      • Ricky Flores 🌴🔥Mavreon Studios🔥🌴 Sigurdur Gunnarsson Lynx🐻 ENMANUEL BIDO Konstantin Mikheev Sean Connolly Rupam Mandal
      4 replies 0 retweets 61 likes
        1. Tim Sweeney‏ @TimSweeneyEpic 29 Dec 2019
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          The other is transactions, hoping we can just write gameplay code using "var<int> Health;" instead of "int health;", write code to minimize unnecessary contention for shared state, and have the engine and API magically sort out concurrency for us.

          12 replies 1 retweet 92 likes
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        2. Jimmie Johnsson‏ @JimmiesCrowns Jan 1
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          Replying to @TimSweeneyEpic

          Data oriented design has got to be the way to go, IMHO. From your garbage collection experiments it seems like your betting on the other alternative though?

          1 reply 0 retweets 0 likes
        3. Tim Sweeney‏ @TimSweeneyEpic Jan 1
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          Replying to @JimmiesCrowns

          Epic isn’t betting on this approach. But I’m betting my two-week coding vacation on it.

          1 reply 0 retweets 5 likes
        4. 3 more replies
        1. Bart‏ @batomaru 30 Dec 2019
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          Replying to @TimSweeneyEpic

          Data oriented approach is not only motivated by parallelism but perhaps more importantly by efficient cache use. It is necessary if you’re hoping to achieve large throughput, naive object oriented approach is a huge waste.

          0 replies 0 retweets 4 likes
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        2. Zino‏ @ohzino 29 Dec 2019
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          Replying to @TimSweeneyEpic

          He's speaking the language of billionares

          2 replies 0 retweets 0 likes
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