[Haskell-cafe] SMP parallelism increasing GC time dramatically

Tom Thorne thomas.thorne21 at gmail.com
Mon Oct 10 16:44:10 CEST 2011

thanks! I just tried setting -A32M and this seems to fix the parallel GC
problems, I now get a speedup with parallel GC on and performance is the
same as passing -qg. I had tried -H before and it only made things worse,
but -A seems to do the trick.

I'm still having problems with segmentation faults though. Depending on how
I apply parMap, and whether I use monad-par or control.parallel, they seem
to come and go arbitrarily. In a successful run that lasted about 30s in
total with control.parallel, +RTS -s reports:
SPARKS: 422712 (394377 converted, 0 pruned)

am I creating too many sparks?

On Mon, Oct 10, 2011 at 3:07 PM, Gregory Collins <greg at gregorycollins.net>wrote:

> On Mon, Oct 10, 2011 at 3:55 PM, Tom Thorne <thomas.thorne21 at gmail.com>
> wrote:
> >
> > Yes I will try to run threadscope on it, I tried it before and the event
> log output produced about 1.8GB, and then crashed.
> > Is there any way to tell the RTS to perform GC less often? My code
> doesn't use too much memory and I'm using fairly hefty machines (e.g one
> with 48 cores and 128GB of RAM) and so perhaps the default/heuristic
> settings aren't optimal.
> Increasing "-A" and "-H" in the RTS options should help with this.
> G
> --
> Gregory Collins <greg at gregorycollins.net>
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