# FunctionWrappers showing ~25x overhead over a native function call

**URL:** <https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323>\
**Category:** General Usage\
**Tags:** question\
**Created:** [June 17, 2017, 8:53am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323 "2017-06-17T08:53:53Z")\
**Posts on this page:** 11\
**Page:** 1

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**Author:** ![Nitin\_Arora](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nitin_arora/32/1174_2.png) [@Nitin\_Arora](https://discourse.julialang.org/u/Nitin_Arora)\
**Post date:** [June 17, 2017, 8:53am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/1 "2017-06-17T08:53:53Z")

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I am seeing performance a big difference between using `FunctionWrappers` and native function call. Is this to be expected ?  
Please see the MWE below:

```julia
using BenchmarkTools  
using FunctionWrappers: FunctionWrapper 

struct A{T}
   x::T
end

get_power(a::A{T}, y::T,z::T) where {T} = a.x + y + z

const Fwarpper = FunctionWrapper{Float64,Tuple{A{Float64},Float64,Float64}}
const dict = Vector{Fwarpper}(1)

dict[1] = Fwarpper(get_power)
a = A(1.5)

@btime @inbounds get_power($a,5.6,7.87);
  0.488 ns (0 allocations: 0 bytes)

@btime @inbounds dict[1]($a,5.6,7.87);
  12.863 ns (0 allocations: 0 bytes)

```

This suggest that there is a ~25X overhead for this case ?  
Is it normal to expect this overhead between explicitly calling a function and calling a function via `FunctionWrappers`?  
It seems like this [post] ([Performance of functions returned from container - #3 by kristoffer.carlsson](https://discourse.julialang.org/t/performance-of-functions-returned-from-container/3747/3)) @yuyichao seemed to suggest there there is no overhead.

My Julia VersionInfo

```nohighlight
Commit 68e911b (2017-05-18 02:31 UTC)
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: Intel(R) Xeon(R) CPU E5-2630 v2 @ 2.60GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Sandybridge)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.9.1 (ORCJIT, ivybridge)

```

I might be doing this all wrong as I am using `FunctionWrappers` for the first time.

thanks!

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<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [June 17, 2017, 9:33am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/2 "2017-06-17T09:33:57Z")

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Firstly, remove the `@inbounds` in front of the `get_power`. It makes the expression not return anything so everything is optimized away. Also, why are you even using it here at all?

Secondly, why are you benchmarking the time it takes to do the dictionary lookup for the FunctionWrapper benchmarking but not for the standard function?

---

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**Author:** ![Nitin\_Arora](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nitin_arora/32/1174_2.png) [@Nitin\_Arora](https://discourse.julialang.org/u/Nitin_Arora)\
**Post date:** [June 17, 2017, 10:12am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/3 "2017-06-17T10:12:17Z")

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Thanks for the reply @kristoffer.carlsson and the `@inbounds` tip. Still have lots to learn. My bad, `Dict` is a bad variable name, its actually just an `1d Array`

I removed the `@inbounds` and tried removing array overhead completely:

```julia
using BenchmarkTools  
using FunctionWrappers: FunctionWrapper 

struct A{T}
   x::T
end

get_power(a::A{T}, y::T,z::T) where {T} = a.x + y + z

const Fwarpper = FunctionWrapper{Float64,Tuple{A{Float64},Float64,Float64}}

f = Fwarpper(get_power)
a = A(1.5)

@btime get_power($a,5.6,7.87);
  2.794 ns (0 allocations: 0 bytes)

@btime $f($a,5.6,7.87);
  10.557 ns (0 allocations: 0 bytes)

```

Now the overhead is ~3.7x, which looks better, but I don’t under why there is any.

thanks.

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<div class="post-metadata">

**Author:** ![dpsanders](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dpsanders/32/3573_2.png) [@dpsanders](https://discourse.julialang.org/u/dpsanders)\
**Post date:** [June 17, 2017, 10:25am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/4 "2017-06-17T10:25:04Z")

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The type of a.x is also Float64 as far as I can see.

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [June 17, 2017, 10:32am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/5 "2017-06-17T10:32:42Z")

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A few things you can do more. Put `@noinline` on `get_power` to prevent it from inlining. Also, FunctionWrappers does a null check for precompilation support.

---

<div class="post-metadata">

**Author:** ![Nitin\_Arora](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nitin_arora/32/1174_2.png) [@Nitin\_Arora](https://discourse.julialang.org/u/Nitin_Arora)\
**Post date:** [June 17, 2017, 10:51am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/6 "2017-06-17T10:51:37Z")

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No sure what you wanted to tell me. I am assuming Julia compiler can infer that.

---

<div class="post-metadata">

**Author:** ![Nitin\_Arora](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nitin_arora/32/1174_2.png) [@Nitin\_Arora](https://discourse.julialang.org/u/Nitin_Arora)\
**Post date:** [June 17, 2017, 10:53am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/7 "2017-06-17T10:53:32Z")

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Just tried your suggestions

```julia
@noinline get_power(a::A{T}, y::T,z::T) where {T} = a.x + y + z

@btime get_power($a,5.6,7.87);
  4.749 ns (0 allocations: 0 bytes)

```

So now the overhead is ~2x, probably due to the null check, which I have no idea how to disable. But this means that there is performance penalty to FunctionWrappers of not having inlining. Am I correct ?

Thanks

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [June 17, 2017, 10:55am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/8 "2017-06-17T10:55:15Z")

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Yes and that is the whole point of the package.

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<div class="post-metadata">

**Author:** ![Nitin\_Arora](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nitin_arora/32/1174_2.png) [@Nitin\_Arora](https://discourse.julialang.org/u/Nitin_Arora)\
**Post date:** [June 17, 2017, 11:11am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/9 "2017-06-17T11:11:26Z")

</div>

Understood. Thanks

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<div class="post-metadata">

**Author:** ![dpsanders](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dpsanders/32/3573_2.png) [@dpsanders](https://discourse.julialang.org/u/dpsanders)\
**Post date:** [June 17, 2017, 11:26am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/10 "2017-06-17T11:26:19Z")

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Sorry, I was confused. Ignore my comment.

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<div class="post-metadata">

**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [June 17, 2017, 11:43am UTC](https://discourse.julialang.org/t/functionwrappers-showing-25x-overhead-over-a-native-function-call/4323/11 "2017-06-17T11:43:52Z")

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This is correct. The main idea of the package is in the julia issue linked in the readme. For this particular property,

> In these cases, it is acceptable that the callback function is not/cannot be inlined to the caller but it is also desired to avoid necessary boxing or runtime type check/dispatch.

In another word, the whole point is the you’ll have a single callsite that can be calling different functions with the same signature that you don’t want to specialize on.