Concurrency and program speed

[Joseph Rushton Wakeling]

On 03/01/2013 11:43 AM, thedeemon wrote:
> Two ideas coming to mind:
> 1) Amdahl's law. If there is some locking inside random numbers generator, you
> will never get linear speed up.

I had some concerns here.  rndGen is supposed to be thread-safe, which was 
incidentally why I was using std.concurrency; I'm not sure if the same safety 
occurs with std.parallelism.

> 2) More probable: the "4 cores" of your laptop might be just 2 cores with
> hyperthreading, that's not honest 4 cores, they won't give you 4x speedup anywhere.

Yes, this turns out to be the case, so is the most likely cause.  Your results 
and Jerro's suggest that with a greater number of true cores, an appropriate 
speedup results.

Thanks to both of you for the thoughts and advice!