Endianness based Entity representation #3788
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james7132
added
A-ECS
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Here's a updated set of benchmarks from my machine (running off of a AMD 5950x). 34 benchmarks saw a tangible improvement, 24 saw a tangible regression in performance. |
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Most pf the regressions don’t look too bad and the overall improvements are substantial especial on 2 or 3 of the benchmarks. I also think that those looking for determinism will be okay having to specify that themselves with regard to endianness of entities as this will not be the only concern they need to make sure they get right when seeking such determinism. I am in favour of this change. LGTM! |
alice-i-cecile
approved these changes
Jan 28, 2022
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In particular, the improvements to the |
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What is niching @alice-i-cecile ? |
The ability to store an |
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Ah yes, that is indeed quite awesome! As far as I can tell this PR should play well with niching. |
MinerSebas
reviewed
Jan 28, 2022
Niching only really has an effect on the assembly generated for constructing an Entity. |
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Reran benchmarks now that we have |
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I'll leave the interpretation to you but here are the results from an M1 Max: |
Weibye
added
the
S-Adopt-Me
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Closing in favor of #10558. |
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Objective
Fixes #2346. Optimize various functions on
Entity. This impacts the performance of all corners of ECS and the engine as a whole.Solution
Use
#[repr(C, align(8))]to makeEntitya pusedo-u64. This is reliant on the endianness of the target platform, so two different definitions of Entity are made, one for little endian and one for big endian. This significantly improves the assembly generated for many operations without adding to the complexity of the type's implementation (see https://godbolt.org/z/jcxY5G9r4). The one major cost is that accessinggenerationby itself requires one more instruction.Since the order of the fields is no longer consistent from platform to platform, a explicit implementation of
PartialOrdis required to enforce correctness. Asto_bitsbecomes a no-op when inlined, this comparison, while looking complex, boils down to a single u64 comparison.This PR aims to get the benefits of #2372 without introducing significant code complexity.