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[vm/ffi] Optimize memcopy in nested struct assignment #43967

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dcharkes opened this issue Oct 28, 2020 · 1 comment
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[vm/ffi] Optimize memcopy in nested struct assignment #43967

dcharkes opened this issue Oct 28, 2020 · 1 comment
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area-vm Use area-vm for VM related issues, including code coverage, and the AOT and JIT backends. library-ffi type-enhancement A request for a change that isn't a bug type-performance Issue relates to performance or code size

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@dcharkes
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dcharkes commented Oct 28, 2020 •
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In https://dart-review.googlesource.com/c/sdk/+/169221 we implement a memcopy function that enables copying:

  • Pointer -> Pointer
  • Pointer -> TypedData
  • TypedData -> Pointer
  • TypedData -> TypedData

We should recognize the memcopy method and implement it with MemoryCopyInstr in the VM for performance.

edit: adding ideas from #48139:

dart:ffi uses the _memCopy helper when working with structs.

We should make sure to

  • Provide fast recognized implementation for this method (probably bottoming in MemoryCopyInstr.
  • Small constant size copies and unroll the copying loop in place.
@dcharkes dcharkes added area-vm Use area-vm for VM related issues, including code coverage, and the AOT and JIT backends. library-ffi labels Oct 28, 2020
@dcharkes dcharkes mentioned this issue Oct 28, 2020
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@mkustermann mkustermann added the type-enhancement A request for a change that isn't a bug label Dec 16, 2020
@dcharkes dcharkes mentioned this issue Mar 25, 2021
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@dcharkes dcharkes added the type-performance Issue relates to performance or code size label Dec 19, 2022
@dcharkes dcharkes mentioned this issue Dec 19, 2022
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2 tasks
copybara-service bot pushed a commit that referenced this issue Dec 29, 2022
@dcharkes
[benchmarks/ffi] Add FfiStructCopy benchmark
a7163db 
`_memCopy` inside `dart:ffi` is currently doing a per-byte copy in
Dart. This is rather slow, we should optimize this with the
`MemoryCopyInstr` in the VM.

This CL adds benchmarks to report the number of bytes copied per
second.

Adds only benchmarks with copies of 32^(0..3), as non-power-of-two
benchmarks did not seem to behave differently.

Since legacy mode is no longer benchmarked, the dart2 version of this
benchmark is omitted.

Benchmarks set up according to
https://dart-review.googlesource.com/c/sdk/+/200188

Bug: #43967
Change-Id: I3d9be8de725820fd3365a7dc85d15174bddc1ae6
Cq-Include-Trybots: luci.dart.try:benchmark-linux-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/277522
Reviewed-by: Jonas Termansen <sortie@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
copybara-service bot pushed a commit that referenced this issue Jan 2, 2023
@dcharkes
[vm/ffi] Optimize struct copies
5d0325d 
Replace the `_memCopy` implementation in Dart with `MemoryCopyInstr`.

Speeds up copying from and to `Pointer`s by up to a 100x for large
structs.

TEST=tests/ffi/function_callbacks_structs_by_value_test.dart

BENCHMARK=benchmarks/FfiStructCopy/dart/FfiStructCopy.dart

Before (x64 JIT):

FfiStructCopy.Copy1Bytes(RunTimeRaw): 86.26189953740506 ns.
FfiStructCopy.Copy16Bytes(RunTimeRaw): 14.006969563521945 ns.
FfiStructCopy.Copy1024Bytes(RunTimeRaw): 8.567228629242734 ns.
FfiStructCopy.Copy65536Bytes(RunTimeRaw): 8.469047080663412 ns.

After (x64 JIT):

FfiStructCopy.Copy1Bytes(RunTimeRaw): 56.79513144264321 ns.
FfiStructCopy.Copy16Bytes(RunTimeRaw): 3.562479879234367 ns.
FfiStructCopy.Copy1024Bytes(RunTimeRaw): 0.10771875669750132 ns.
FfiStructCopy.Copy65536Bytes(RunTimeRaw): 0.02758346614218262 ns.

Bug: #43967
Change-Id: I5d51c39a13b8c9522ee88d81bba7365caef70a27
Cq-Include-Trybots: luci.dart.try:vm-ffi-android-debug-arm-try,vm-ffi-android-debug-arm64c-try,vm-precomp-ffi-qemu-linux-release-arm-try,vm-precomp-ffi-qemu-linux-release-riscv64-try,vm-kernel-reload-rollback-linux-debug-x64-try,vm-kernel-reload-linux-debug-x64-try,vm-kernel-nnbd-mac-debug-arm64-try,vm-kernel-nnbd-mac-debug-x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-debug-x64c-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/277523
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Aske Simon Christensen <askesc@google.com>
@dcharkes
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Small constant size copies and unroll the copying loop in place.

Tracking in:

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