mblazevic:

On Fri 22/05/09 10:51 AM , John Lato jwlato@gmail.com sent:

...

Hi Mario,

It looks like the parallelize function is getting inlined when it's in the same file, but not when it's in a separate file.

Adding a {-# INLINE parallelize #-} pragma to the module with parallelize recovers all the performance for me.

You could probably see exactly what's happening in more detail by going through the Core output.

Thank you, this advice helped. The Core output indicates that function `test' evaluates the arguments to `parallelize' before it calls it. In other words, the call to `parallelize' is optimized as a strict function call -- which it is. The problem is that this optimization evaluates the arguments sequentially. Compiling with optimizations turned off regains the parallel execution.

I guess I will report this as a GHC bug. Or is it a feature request?

As Duncan suggessted, try with GHC head (grab a snapshot). `par` et al are much improved. -- Don