[erlang-questions] Application granularity (was: Parallel Shootout & a style question)

Mats Cronqvist <>
Fri Sep 5 10:02:15 CEST 2008


Jay Nelson wrote:
> ... in response to a flurry of messages about automatically  
> parallelizing list comprehensions ...
>
> If I go through all the code I have written and count the number of  
> list comprehensions relative to the total amount of code, there are  
> not that many occurrences to worry about.  The length of each  
> comprehension's data set is not that great in typical code, and  
> unless it is a very data parallel algorithm such as matrix  
> manipulation, there is little to be gained overall.  Mats toss off of  
> 10% would over-estimate the likely benefit in the code I typically  
> have to implement.
>   

  agreed. parallelizing list comprehensions will accomplish nothing in 
phone switch/web server type applications. but that's not what i'm 
talking about either. to quote myself;

  "in an ideal world, all the basic OTP libs should be rewritten to be 
parallel."

{snipped some stuff i more or less agree with}
> I believe the compiler writers and tool builders should focus on  
> making it easier to produce more numerous, but smaller processes,  
> rather than trying to make the sequential code eke out an additional  
> 10% of performance.  I want my code to run 1000x faster when I get a  
> 1000 core machine.  I likely will need 100,000 processes to realize  
> that goal.

  the problem is that it doesn't really matter how many processes you 
have. to make use of a 1,000 core machine you'll need to have 1,000 
*runnable* processes at any one time.
  E.g. a large phone switch, that handles 10,000 ongoing calls, will 
typically have ~10 runnable processes (given that you model a call as a 
process). I.e. for such a system it will buy you nothing to use more 
than 10 cores.

  mats



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