Benchmarking from the REPL broken without wrapper function?

[jakebolewski]

julia> f(x) =  sin(sin(sin(sin(sin(sin(sin(x)))))))
f (generic function with 1 method)

julia> @benchmark f(3.33)
================ Benchmark Results ========================
     Time per evaluation: 84.60 ns [84.40 ns, 84.80 ns]
Proportion of time in GC: 0.00% [0.00%, 0.00%]
        Memory allocated: 0.00 bytes
   Number of allocations: 0 allocations
       Number of samples: 8301
   Number of evaluations: 5454801
         R² of OLS model: 0.999
 Time spent benchmarking: 0.50 s

julia> y(x) = sin(x)
y (generic function with 1 method)

julia> @benchmark y(3.33)
================ Benchmark Results ========================
     Time per evaluation: 13.86 ns [13.70 ns, 14.03 ns]
Proportion of time in GC: 0.00% [0.00%, 0.00%]
        Memory allocated: 0.00 bytes
   Number of allocations: 0 allocations
       Number of samples: 10201
   Number of evaluations: 33352001
         R² of OLS model: 0.962
 Time spent benchmarking: 0.51 s

julia> @benchmark sin(sin(sin(sin(sin(sin(sin(3.33)))))))
================ Benchmark Results ========================
     Time per evaluation: 6.53 ns [6.49 ns, 6.57 ns]
Proportion of time in GC: 0.00% [0.00%, 0.00%]
        Memory allocated: 0.00 bytes
   Number of allocations: 0 allocations
       Number of samples: 11001
   Number of evaluations: 71490001
         R² of OLS model: 0.989
 Time spent benchmarking: 0.53 s

julia> @benchmark sin(3.33)
================ Benchmark Results ========================
     Time per evaluation: 13.66 ns [13.52 ns, 13.80 ns]
Proportion of time in GC: 0.00% [0.00%, 0.00%]
        Memory allocated: 0.00 bytes
   Number of allocations: 0 allocations
       Number of samples: 10201
   Number of evaluations: 33352001
         R² of OLS model: 0.970
 Time spent benchmarking: 0.50 s

[johnmyleswhite]

I think this is because we removed the no-online from here: https://github.com/johnmyleswhite/Benchmarks.jl/blob/f5ef97e2ca1adf80c47064f8616e77b4b76b3b8c/src/benchmarkable.jl#L68

[johnmyleswhite]

At some point, we need to pick a set of N examples that we want to get right and see whether that's actually achievable at all. As is, we seem to be oscillating because it's not clear there is a single correct solution.

[johnmyleswhite]

cc @mbauman

[mbauman]

Working as intended (but needs to be documented).

The latest swing of the pendulum has @benchmark working with the same semantics as the @code_* macros — it evaluates all arguments and only benchmarks the outermost function.

[mbauman]

Oh, wait, I missed the factor of two difference between @benchmark sin(3.33) and @benchmark sin(sin(3.33)). That's definitely wonky.

Edit: Aha, that's because sin's performance is dependent upon its inputs. I imagine that it's doing extra work to bring 3.33 into the domain it works in. @benchmark sin(-.18) has comparable performance to sin(sin(3.33)).

[johnmyleswhite]

What does sin(-0.18729466354290317) produce? I assume there's no real speed difference, but worth making sure.

[mbauman]

(Yah, see my edit.)

[johnmyleswhite]

Ok. Do you mind documenting this, Matt? You clearly have a better understanding of how we ended up with the current approach.

[mbauman]

Sure, I can throw something together this weekend.

[johnmyleswhite]

Many, many thanks.

[jakebolewski]

Ok, that make's sense. Thanks for the clarification.