[erlang-questions] My frustration with Erlang

Paul Fisher <>
Fri Sep 12 17:00:19 CEST 2008

Joel Reymont wrote:
> These are gen_server call timeouts when requests for game information
> take longer than the default 5 seconds. I have an average of 5 players
> per game so this is not because a large number of processes are trying
> to access the game.
> I suppose this is a reflection of the load on the system, although CPU
> usage never goes past 300% which tells me that no more than 3 cores
> are used by Erlang.

We have a system with a completely different workload profile, but our 
initial testing has indicated a SMP scaling barrier, such that scaling 
beyond 4 cores (on x86-64 linux 2.6.24 w/R12-3) deteriorate quickly.

My very preliminary in investigations indicated a substantial number of 
futex system calls (which should happen only on contended locks which 
need kernel arbitrartion) as the work scaled toward 4 cores.  I had 
initially thought that this was related to the amount of work we perform 
in linked in drivers via async threads, but some more current 
information indicates that this might be more core scheduler related.

Can anyone with experiences running a sufficiently complex system on 8+ 
core systems share your experiences?  I would love to hear from someone 
intimate with the SMP implementation on the state of affairs and 
possible future directions.


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