Slower than System.Random?

[Boarders]

I wrote a tiny utility for performing a Fisher–Yates shuffle here. At first I wrote this using System.Random and StdGen but was informed this was supposedly extremely slow. I then updated to use this library here. Surprisingly this led to worse performance on every experiment that I ran. Is this the wrong use case for this library (e.g. generating a million Ints between from i to 1000000 as i goes from 1 to 999999)? Or am I doing something else wrong? I did make sure to only generate a single generator but I am not very informed about the ins-and-outs of RNG and so this might simply be an inappropriate use case.

[Shimuuar]

I only glanced at code. I can't see anything obviously wrong but I suspect that problem is lack of specialization. You could try to add INLINE/SPECIALIZE pragmas to the worker functions in Mutable.Shuffle

[sheaf]

Here's a simplistic benchmark: BenchShuffle.zip.
Switch the random number generator on line 40 of BenchShuffle.hs, and switch to the corresponding branch of @Boarders' perfect-vector-shuffle library in the cabal.project file, to compare MWC with System.Random. The results I have obtained are as follows:

random-1.1

shuffle/10^6
                    | lower bound | estimate | upper bound
OLS regression      | 1.31 s      | 1.32 s   | 1.34 s
R² goodness-of-fit  | 1.000       | 1.000    | 1.000
Mean execution time | 1.30 s      | 1.31 s   | 1.31 s
Standard deviation  | 6.10 ms     | 7.48 ms  | 8.56 ms

mwc-random-0.14.0.0

shuffle/10^6
                    | lower bound | estimate | upper bound
OLS regression      | 1.94 s      | 1.97 s   | 1.98 s
R² goodness-of-fit  | 1.000       | 1.000    | 1.000
Mean execution time | 1.97 s      | 1.98 s   | 1.98 s
Standard deviation  | 2.76 ms     | 4.49 ms  | 5.48 ms

and for comparison tf-random-0.5:

shuffle/10^6
                     | lower bound | estimate | upper bound
OLS regression       | 970 ms      | 1.05 s   | 1.08 s
R² goodness-of-fit   | 0.999       | 0.999    | 1.000
Mean execution time  | 1.04 s      | 1.05 s   | 1.06 s
Standard deviation   | 10.6 ms     | 12.7 ms  | 14.0 ms

[Boarders]

@Shimuuar : Adding INLINE, SPECIALISE, INLINEABLE and the ghc-options -fexpose-all-unfoldings
and -fspecialize-aggressively seems to make no difference and it is still significantly slower than System.Random without any of those added (it also does not seem to affect the performance if I add those pragmas there though).

[Shimuuar]

I tried to reproduce issue and wasn't able to build reproducer. Is this still actual?