[erlang-questions] RE gen_server bottleneck

Olivier BOUDEVILLE <>
Fri Dec 14 18:02:46 CET 2012


Hello Sarva,

I suppose it depends on how scalable you want to be; I think the first 
approach is to lean first on your simulation algorithm; is the management 
of your discrete time event-driven or time-stepped?
In either case you have solutions to implement a parallel evaluation of 
model instances with Erlang (for example, in the first case, with a 
conservative or optimistic scheduling), knowing that maintaining a 
centralised event queue on which the engine would iterate sequentially 
will induce by design immediate bottlenecks.

Once the parallel algorithm is implemented (most probably making use of 
SMP resources), to obtain further scalability gains it is probably useful 
to split it into, say, a tree of time managers where communications 
between time managers could be a lot terser than between a time manager 
and the local model instances it would manage; this would open the way to 
a still more parallel mode of operation - and would immediately offer the 
opportunity for distribution, which might be efficient, at least to some 
extent.

Finally I would go for a raise in the priority of the time manager 
processes and other key simulation services, efficient data-structures for 
scheduling, load balancing and smart placement of model instances to 
minimize the number of messages sent over the network and the induced 
latency. 

Then only I would go for fancy hardware, detailed profiling, native 
compilation, C-nodes and the like!

<plug>
At least it is the path we are going through with Sim-Diasca (which is an 
open-source generic discrete-time simulation engine, maybe not too far 
from what you intend to do, cf http://www.sim-diasca.com). In this 
process, we are currently just before the profiling.
</plug>

Hope this helps!

Best regards,

Olivier.
---------------------------
Olivier Boudeville

EDF R&D : 1, avenue du Général de Gaulle, 92140 Clamart, France
Département SINETICS, groupe ASICS (I2A), bureau B-226
Office : +33 1 47 65 59 58 / Mobile : +33 6 16 83 37 22 / Fax : +33 1 47 
65 27 13

 a écrit sur 14/12/2012 14:39:07 :

> Hi all,
>         I have been trying to write a network simulator in Erlang 
> modelled on ns-3. The code can be found at 
https://github.com/avras/nsime
> 
> NSIME is a discrete event simulator where a registered gen_server 
> process nsime_simulator holds all the events to be simulated in a 
> gb_trees sorted by event time. This process has become a bottlneck 
> when the simulation is large as multiple entities try to schedule 
> events by doing a call on the single nsime_simulator process. I am 
> still a newbie in Erlang profiling so this is more of a hunch 
> arising from running the example scenarios. 
> 
> How can I remove this bottleneck?
> 
> Thanks in advance
> sarva_______________________________________________
> erlang-questions mailing list
> 
> http://erlang.org/mailman/listinfo/erlang-questions



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