[Merged by Bors] - Skip drop when needs_drop is false
#4773
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DJMcNab
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bjorn3
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May 16, 2022
DJMcNab
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May 16, 2022
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@bjorn3 I've left this in for now, as I'm struggling to find a compelling argument for running Cleanup and clearing the entities to have no differentiation. Perhaps it should be nested, but that's a different question to what you were requesting.
james7132
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May 16, 2022
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LGTM other than the existing review comments. I was a bit suspicious of adding a branch in the hotpath for deleting/moving entities around, but it makes sense that a branch would be preferable to what is effectively a virtual function call that POD components don't use.
bjorn3
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May 16, 2022
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alice-i-cecile
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May 16, 2022
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
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May 17, 2022
# Objective - We do a lot of function pointer calls in a hot loop (clearing entities in render). This is slow, since calling function pointers cannot be optimised out. We can avoid that in the cases where the function call is a no-op. - Alternative to #2897 - On my machine, in `many_cubes`, this reduces dropping time from ~150μs to ~80μs. ## Solution - Make `drop` in `BlobVec` an `Option`, recording whether the given drop impl is required or not. - Note that this does add branching in some cases - we could consider splitting this into two fields, i.e. unconditionally call the `drop` fn pointer. - My intuition of how often types stored in `World` should have non-trivial drops makes me think that would be slower, however. N.B. Even once this lands, we should still test having a 'drop_multiple' variant - for types with a real `Drop` impl, the current implementation is definitely optimal.
bors
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drop when needs_drop is falsedrop when needs_drop is false
robtfm
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May 17, 2022
# Objective - We do a lot of function pointer calls in a hot loop (clearing entities in render). This is slow, since calling function pointers cannot be optimised out. We can avoid that in the cases where the function call is a no-op. - Alternative to bevyengine#2897 - On my machine, in `many_cubes`, this reduces dropping time from ~150μs to ~80μs. ## Solution - Make `drop` in `BlobVec` an `Option`, recording whether the given drop impl is required or not. - Note that this does add branching in some cases - we could consider splitting this into two fields, i.e. unconditionally call the `drop` fn pointer. - My intuition of how often types stored in `World` should have non-trivial drops makes me think that would be slower, however. N.B. Even once this lands, we should still test having a 'drop_multiple' variant - for types with a real `Drop` impl, the current implementation is definitely optimal.
exjam
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May 22, 2022
# Objective - We do a lot of function pointer calls in a hot loop (clearing entities in render). This is slow, since calling function pointers cannot be optimised out. We can avoid that in the cases where the function call is a no-op. - Alternative to bevyengine#2897 - On my machine, in `many_cubes`, this reduces dropping time from ~150μs to ~80μs. ## Solution - Make `drop` in `BlobVec` an `Option`, recording whether the given drop impl is required or not. - Note that this does add branching in some cases - we could consider splitting this into two fields, i.e. unconditionally call the `drop` fn pointer. - My intuition of how often types stored in `World` should have non-trivial drops makes me think that would be slower, however. N.B. Even once this lands, we should still test having a 'drop_multiple' variant - for types with a real `Drop` impl, the current implementation is definitely optimal.
ItsDoot
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Feb 1, 2023
# Objective - We do a lot of function pointer calls in a hot loop (clearing entities in render). This is slow, since calling function pointers cannot be optimised out. We can avoid that in the cases where the function call is a no-op. - Alternative to bevyengine#2897 - On my machine, in `many_cubes`, this reduces dropping time from ~150μs to ~80μs. ## Solution - Make `drop` in `BlobVec` an `Option`, recording whether the given drop impl is required or not. - Note that this does add branching in some cases - we could consider splitting this into two fields, i.e. unconditionally call the `drop` fn pointer. - My intuition of how often types stored in `World` should have non-trivial drops makes me think that would be slower, however. N.B. Even once this lands, we should still test having a 'drop_multiple' variant - for types with a real `Drop` impl, the current implementation is definitely optimal.
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Objective
many_cubes, this reduces dropping time from ~150μs to ~80μs.Solution
dropinBlobVecanOption, recording whether the given drop impl is required or not.dropfn pointer.Worldshould have non-trivial drops makes me think that would be slower, however.N.B. Even once this lands, we should still test having a 'drop_multiple' variant - for types with a real
Dropimpl, the current implementation is definitely optimal.