Speed up rkyv serialization #123
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Jasper-Bekkers
commented
Jan 24, 2023
| @@ -98,7 +98,7 @@ bitflags! { | |||
| #[cfg_attr(feature = "cuda", derive(cust_core::DeviceCopy))] | |||
| #[derive(Default)] | |||
| /// The status of a QBVH node. | |||
| pub struct QbvhNodeFlags: u8 { | |||
| pub struct QbvhNodeFlags: u64 { | |||
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This particular change is the one I wanted to highlight / discuss.
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This tries to make use of the rkyv
CopyOptimizeattribute that can guarantee memcpy-able structs are indeed just that, rather then iterating over each element in the vector.This ran into one oddity however, the archived layout of
QbvhNodeis smaller then the regular layout (128 vs 124 bytes), this is becauseQbvhNodecontains quite a few padding bytes.QbvhNodeFlagsisu8NodeIndexhas au8memberBoth of those cause a (normally) 121-bytes struct to get blown up to 128 bytes.
In this PR I've hackfixed/worked around this issue by making QbvhNodeFlags u64 which obviously isn't what anybody would want, however since I'm not familiar with this project I'd like to open the discussion about what to do with this.
It seems likely that
QbvhNodeneeds to be somehow cache-line aligned (which it is at the moment), but it might be nice to mark the padding bytes inNodeIndexandQbvhNodeexplicitly so it's clear where in the node one can stuff some additional info.Removing the
CopyOptimizeis not the end of the world; but in this case having it speeds up rkyv serialization by about 2x.