Parallel GHC on Altix?

Simon Marlow simonmarhaskell at
Fri May 12 09:05:26 EDT 2006

Bulat Ziganshin wrote:

> moreover, afaiu, this means that ghc-compiled programs will no more
> stall for several seconds doing major GC that is also very important
> for any user-interactive program (especially games :) )

Unfortunately it won't completely remove the latency of a major GC, 
although latency will be reduced because the GC is quicker (hopefully).

Parallel GC is when the whole system stops and performs multi-threaded 
GC, as opposed to "concurrent GC", which is when the GC runs 
concurrently with the program.  We think concurrent GC is unlikely to be 
practical in the Haskell setting, due to the extra synchronisation 
needed in the mutator.  However, there may always be clever techniques 
that we haven't discovered, and synchronisation might become less 
expensive, so the balance may change in the future.


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