-prof, -threaded, and -N

[Lars Kuhtz]

From https://github.com/ghc/ghc/blob/master/rts/RtsFlags.c#L1238 it seems that the behavior described in my email below is intended:

```

                if (rts_argv[arg][2] == '\0') {
#if defined(PROFILING)
                    RtsFlags.ParFlags.nNodes = 1;
#else
                    RtsFlags.ParFlags.nNodes = getNumberOfProcessors();
#endif
```

So, my question is: what is the reason for this difference between the profiling and the non-profiling case?

Lars

> On Jun 2, 2015, at 10:20 PM, Lars Kuhtz <haskell at kuhtz.eu> wrote:
> 
> Hi,
> 
> The behavior of the -N flag (without argument) with the profiling runtime seems inconsistent compared to the behavior without profiling. The following program
> 
> ```
> module Main where
> 
> import GHC.Conc
> 
> main :: IO ()
> main = print numCapabilities
> ```
> 
> when compiled with `ghc -threaded -fforce-recomp Prof.hs` and run as `./Prof +RTS -N` prints `2` on my machine. When the same program is compiled with `ghc -threaded -fforce-recomp -prof Prof.hs` and executed as `./Prof +RTS -N` it prints `1`.
> 
> When an argument is provided to `-N` (e.g. `./Prof +RTS -N2`) the profiling and non-profiling versions behave the same.
> 
> I tested this with GHC-7.10.1 but I think that I already observed the same behavior with GHC-7.8.
> 
> Is this inconsistency intended?
> 
> Lars
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