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

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 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 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 :

...

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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