[Haskell-cafe] optimising for vector units

[Jan-Willem Maessen - Sun Labs East]

Ronny Wichers Schreur wrote:
> Jan-Willem Maessen writes (in the Haskell Cafe):
> 
>> My ultimate goal was parallelization.  However, I'm now convinced it 
>> would take about 2-3 programmer-years more of effort to realize that 
>> goal.  Parallel garbage collection (which is *not* optional on a 
>> parallel Haskell implementation, as our experience with pH 
>> demonstrated) and very fine-grained thunk-update protocols are both 
>> tricky technical challenges.  And that leaves aside the question of 
>> whether there's enough coarse-grained work buried among all that 
>> fine-grained work to make it all worthwhile. 
> 
> 
> I'm not sure how to interpret this. Will you also have solved
> the granularity problem in these two to three years?

Probably not.  One might hope to do well by choosing an appropriate 
schedule (favor leaves locally, roots when work is moved between 
processors).  But there's no evidence generating the work lazily would 
even leave enough work to be done.

There's a difference between a system that would work (and probably 
work OK for 2-4 processors) and a system that would scale.  The latter 
would also require some hard thought by the application programmer, as 
well.

-Jan-Willem Maessen