[Haskell-cafe] Why is Haskell so slow (comparing to Java/Scala)?

[Thomas DuBuisson]

To recap

You claimed a 40ms measurement.  If we use `for_` instead of `void $
for` (for reasons mentioned earlier in the thread) and `-O2` when
compiling we get just under 1 ms:

```
time                 876.2 μs   (852.8 μs .. 896.9 μs)
                     0.994 R²   (0.989 R² .. 0.998 R²)
mean                 838.4 μs   (825.0 μs .. 855.5 μs)
std dev              48.21 μs   (36.91 μs .. 74.18 μs)
variance introduced by outliers: 48% (moderately inflated)
```

Cheers,
Thomas




On Wed, Sep 20, 2017 at 7:27 AM, Станислав Черничкин
<schernichkin at gmail.com> wrote:
> I've wrote simple Haskell benchmark program, which populated primitive
> vector from vector package:
>
> import           Data.Vector.Primitive.Mutable as P
>
> vectorBench :: Benchmark
> vectorBench = bgroup "vector" [ primitive ]
>   where
>     primitive = bgroup "primitive" [ write1M ]
>       where
>         write1M =  bench "write1M" $ nfIO $ do
>           v <- P.unsafeNew 1000000
>           void $ for [0..1000000 - 1] $ flip (P.unsafeWrite v) (1 :: Int)
>           return ()
>
> I use `unsafeNew` to skip memory initialization and `unsafeWrite` to skip
> boundary checks, I guess it's fastest possible way to write something to
> vector. My result was about 40 ms.
>
> I wrote similar program in Scala:
>
> for (_ <- 1 to 5) {
>   val start = System.currentTimeMillis()
>   val a = new Array[Long](1000000)
>   for (i <- 0 until 1000000) {
>     a(i) = 1L
>   }
>   val end = System.currentTimeMillis()
>   println(s"${end - start} ms")
> }
>
> I skip neither boundary checks nor memory initialization, I also used
> generic array here (suitable for any types of objects, not just for
> primitive types), so I expected longer run time. But what I got was
> shocking:
>
> 7 ms
> 3 ms
> 2 ms
> 1 ms
> 2 ms
>
> This program runs 20-40 times faster than Haskell after warm-up. 20-40
> times, Carl! Why is Haskell soo slooooow? How can it be?
>
>
> --
> Sincerely, Stanislav Chernichkin.
>
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