Having trouble with parallel Haskell

Simon Marlow marlowsd at gmail.com
Thu Jun 5 05:47:45 EDT 2008

Bryan O'Sullivan wrote:
> Isaac Dupree wrote:
>> (no idea if that's relevant, though)
> I can't tell either.  It doesn't seem to make a difference, at any rate.
> By the way, I notice that the threaded RTS blocks signals for long
> periods of time when I run this program.  If I hit control-C, it takes
> several seconds for the program to notice.

This is usually a symptom of a program that does a lot of allocation-less 
computation (or also, long GCs).  When the program isn't allocating, the 
scheduler never runs, and ^C doesn't get serviced.

Allocation-less computation will also hurt parallelism, because the 
load-balancing only happens when the scheduler runs.  This often crops up 
when people try to parallelism small benchmarks (e.g. fib).  It's certainly 
a problem, and we don't have a good solution yet.


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