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[performance] Avoid uneccesary vector copies in imperative_utils.cc #14665

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Apr 16, 2019
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[performance] Avoid uneccesary vector copies in imperative_utils.cc #14665

merged 1 commit into from
Apr 16, 2019

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larroy
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@larroy larroy commented Apr 10, 2019

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@larroy larroy changed the title Avoid uneccesary vector copies in imperative_utils.cc [performance] Avoid uneccesary vector copies in imperative_utils.cc Apr 10, 2019
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larroy commented Apr 10, 2019

@mxnet-label-bot add [performance,pr-awaiting-review]

@marcoabreu marcoabreu added Performance pr-awaiting-review PR is waiting for code review labels Apr 10, 2019
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larroy commented Apr 10, 2019

@mxnet-label-bot add [backend,memory]

@marcoabreu marcoabreu added Backend Issues related to the backend of MXNet Memory labels Apr 10, 2019
yuxihu
yuxihu reviewed Apr 10, 2019
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src/imperative/imperative_utils.cc
inline std::vector<NDArray*> NodeInputs(const nnvm::IndexedGraph& idx,
const int node_idx,
const std::vector<NDArray*> arrays) {
std::vector<NDArray*> NodeInputs(const nnvm::IndexedGraph& idx,
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Can we pass in the returned vector std::vector<NDArray*> so we can save another copy?

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This would be unnecessary and non idiomatic. Return value optimization (RVO) will kick in and eliminate any extra copies on return values.

https://shaharmike.com/cpp/rvo/

src/imperative/imperative_utils.cc
inline std::vector<NDArray*> NodeOutputs(const nnvm::IndexedGraph& idx,
const int node_idx,
const std::vector<NDArray*> arrays) {
std::vector<NDArray*> NodeOutputs(const nnvm::IndexedGraph& idx,
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Can we pass in the returned vector std::vector<NDArray*> so we can save another copy?

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I think there will be not any another copy because of the right-value reference of std::vector.

src/imperative/imperative_utils.cc
inline std::vector<OpReqType> NodeReq(const nnvm::IndexedGraph& idx,
const int node_idx,
const std::vector<OpReqType> array_reqs) {
std::vector<OpReqType> NodeReq(const nnvm::IndexedGraph& idx,
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Can we pass in the returned vector std::vector<OpReqType> so we can save another copy?

src/imperative/imperative_utils.cc

inline std::vector<NDArray*> NodeInputs(const nnvm::IndexedGraph& idx,
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Why remove inline?

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What's the point of inline here? These are private functions so they are moved to anonymous namespace. Let the compiler do the inline as the compiler is better at this than us. We are abusing inline in the codebase.

https://stackoverflow.com/questions/1932311/when-to-use-inline-function-and-when-not-to-use-it

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Can we measure the impact here? Because this logic is part of core engine and gets exposed to every job, I was wondering if it would be good to measure the performance impact.

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yuxihu approved these changes Apr 10, 2019
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LGTM.

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wkcn approved these changes Apr 15, 2019
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LGTM. Thank you for the fix!

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larroy commented Apr 15, 2019

@mxnet-label-bot add [pr-awaiting-merge]

@marcoabreu marcoabreu added the pr-awaiting-merge Review and CI is complete. Ready to Merge label Apr 15, 2019
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larroy commented Apr 15, 2019

@mxnet-label-bot remove [pr-awaiting-review]

@marcoabreu marcoabreu removed the pr-awaiting-review PR is waiting for code review label Apr 15, 2019
@wkcn wkcn merged commit 413fe97 into apache:master Apr 16, 2019
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wkcn commented Apr 16, 2019

Merged. Thank you!

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@larroy - I had quick question on this PR - Can we measure the impact here?

kedarbellare pushed a commit to kedarbellare/incubator-mxnet that referenced this pull request Apr 20, 2019
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Avoid uneccesary vector copies in imperative_utils.cc (apache#14665)
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larroy commented Apr 22, 2019

@sandeep-krishnamurthy Do we have some default go-to performance metric for our countributions? I find this would be very useful.

@junrushao junrushao mentioned this pull request Jun 18, 2019
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haohuanw pushed a commit to haohuanw/incubator-mxnet that referenced this pull request Jun 23, 2019
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Avoid uneccesary vector copies in imperative_utils.cc (apache#14665)
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