[Haskell-cafe] Reasoning about performance

[Carter Schonwald]

Awesome/ thanks for sharing.  It's worth noting that criterion is also
pretty great for microbenchmarks too. On my machine I get pretty good
timing accuracy on anything that takes more than 20 nanoseconds.

On Wednesday, September 4, 2013, Scott Pakin wrote:

> On 09/03/2013 06:02 PM, Carter Schonwald wrote:
>
>> It's also worth adding that ghci does a lot less optimization than ghc.
>>
>
> Yes, I discovered that before I posted.  Note from my initial message
> that I used ghc to compile, then loaded the compiled module into ghci:
>
>      Prelude> :!ghc -c -O2 allpairs.hs
>      Prelude> :load allpairs
>      Ok, modules loaded: AllPairs.
>      Prelude AllPairs> :m +Control.DeepSeq
>      Prelude Control.DeepSeq AllPairs> :show modules
>      AllPairs         ( allpairs.hs, allpairs.o )
>
>  Likewise, the best tool for doing performance benchmarking is the
>> excellent Criterion library.
>>
>
> Ah, I didn't know about Criterion; that does look useful.  For the
> record, here's what Criterion reports for my three all-pairs
> implementations:
>
>     Prelude Criterion.Main AllPairs> defaultMain [bench "allPairs1" $ nf
> allPairs1 [1..10000]]
>                                  ...
>     mean: 5.184160 s, lb 5.156169 s, ub 5.212516 s, ci 0.950
>     std dev: 144.4938 ms, lb 127.3414 ms, ub 164.8774 ms, ci 0.950
>
>     Prelude Criterion.Main AllPairs> defaultMain [bench "allPairs2" $ nf
> allPairs2 [1..10000]]
>                                  ...
>     mean: 2.310527 s, lb 2.290451 s, ub 2.329349 s, ci 0.950
>
>     Prelude Criterion.Main AllPairs> defaultMain [bench "allPairs3" $ nf
> allPairs3 [1..10000]]
>                                  ...
>     mean: 10.05609 s, lb 10.02453 s, ub 10.08866 s, ci 0.950
>
> As before, allPairs2 is the fastest, followed by allPairs1, with
> allPairs3 in last place.
>
> -- Scott
>
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