[Haskell-cafe] Significant slow-down in parallel code?

[Neil Mitchell]

There was a paper at the Haskell Symposium 2009, and the video is
online: http://www.vimeo.com/6680185

Thanks, Neil

On Tue, Jan 5, 2010 at 2:23 AM, Jamie Morgenstern
<cantthinkthinkpink at gmail.com> wrote:
> I am using 6.12... are there any good pointers as to how one uses
> threadscope?
>
> On Mon, Jan 4, 2010 at 3:14 PM, Neil Mitchell <ndmitchell at gmail.com> wrote:
>>
>> Hi Jamie,
>>
>> First question, what version of GHC are you using? There are
>> significant performance improvements to parallel code in GHC 6.12, so
>> it's worth an upgrade. Once you've upgraded you might want to try out
>> threadscope which is designed to help track down these sorts of
>> problems.
>>
>> If you are using 6.10, I recommend turning off parallel garbage
>> collection with the RTS flags (see the manual) as that can cause
>> slowdowns.
>>
>> Thanks, Neil
>>
>> 2010/1/4 Jamie Morgenstern <cantthinkthinkpink at gmail.com>:
>> > Hello;
>> >
>> >  I have a piece of code in which I employ the `par` construct to add
>> > some implicit parallelism
>> > to a theorem prover. However, when running the *same* code with
>> >
>> > +RTS -N1
>> > +RTS -N5
>> > +RTS -N10
>> >
>> > I see a huge slowdown (a factor of 50 with 5 processes and a factor of
>> > 100 for 10 on an 8-core machine).
>> >
>> > Very little time is being spent using the garbage collector. Any
>> > suggestions?
>> >
>> > Thanks,
>> > -Jamie
>> >
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>> >
>
>