Re: [Haskell-cafe] Automatic parallelism in Haskell, similar to "make -j4"?

t.r.willingham:

On Sun, Nov 2, 2008 at 6:44 PM, Bulat Ziganshin wrote:

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What would it take to implement a -j equivalent for, say, GHC? Or if this is not possible, what is wrong with my reasoning?

problem is that make have rather large pices of work which it can run parallel. if ghc will try to parallel every machine operation, it will pend more time maintaining these jobs. 'par' is just the way to tell GHC "this part of job is large enough"

Right, but couldn't the Haskell complier+runtime discover "rather large pieces of work"?

Requires runtime profiling to work out the costs. See this paper which implements this this idea, PDF http://research.microsoft.com/~tharris/papers/2007-fdip.pdf HTML http://209.85.173.104/search?q=cache:7cC4fQjCEH4J:research.microsoft.com/~th... Note that for subsets of Haskell, where we have more information statically about the costs involves, we can do the parallelism automatically. Data Parallel Haskell is the prime example. -- Don