> Something like this might work, not sure what the canonical way is.
> (...)
This is basically the same as the answer I was given on SO. My concerns about
this solutions are:
- rnf requires its parameter to belong to NFData type class. This is not the
case for some data
structures like Repa arrays.
- evaluate only evaluates its argument to WHNF - is this enough? If I have a
tuple containing two
lists won't this only evaluate the tuple construtor and leave the lists as
thunks? This is
actually the case in my code.
As I said previously, it seems that Criterion somehow evaluates the data so
that time needed for
its creation is not included in the benchmark. I modified my dataBuild function
to look lik this:
dataBuild gen = unsafePerformIO $ do
let x = (take 6 $ randoms gen, take 2048 $ randoms gen)
delayThread 1000000
return x
When I ran the benchmark, criterion estimated the time needed to complete it to
over 100 seconds
(which means that delayThread worked and was used as a basis for estimation),
but the benchamrk
was finished much faster and there was no difference in the final result
comparing to the normal
dataBuild function. This suggests that once data was created and used for
estimation, the
dataBuild function was not used again. The main question is: is this
observation correct? In this
question on SO:
http://stackoverflow.com/questions/6637968/how-to-use-criterion-to-measure-performance-of-haskell-programs
one of the aswers says that there is no automatic memoization, while it looks
that in fact the
values of dataBuild are memoized. I have a feeling that I am misunderstanding
something.
> I don't know if you have already read them,
> but Tibell's slides on High Performance Haskell are pretty good:
>
> http://www.slideshare.net/tibbe/highperformance-haskell
>
> There is a section at the end where he runs several tests using Criterion.
I skimmed the slides and slide 59 seems to show that my concerns regarding WHNF
might be true.
Janek
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