[erlang-questions] Re: Unicast 20k messages, $500-$1000 bounty

Paulo Sérgio Almeida <>
Thu Jul 16 22:47:09 CEST 2009


Joel Reymont wrote:
> 
> On Jul 16, 2009, at 6:18 PM, Cliff Moon wrote:
> 
>> The problem you're seeing there is process scheduling overhead.  In 
>> the fun it sends a message and it's doing an ungodly amount of context 
>> switching.  The way to get around this is to bump the process priority 
>> level of the process which iterates the ets table.

I don't think the pubsub causes a huge amount of context switching. 
Sending a message in itself should not cause context switching. But 
there is in fact a huge amount of context switching due to the 2 *  20k 
middlemen.

This means that even if the pubsub is preempted a single time, it will 
have to wait for a lot of switching before resuming the sending. Making 
the pubsub priority high makes it complete the sending to everyone 
before being preempted.

However, I still think that performance should improve noticeably if 
there is one less hop of middlemen: it will be at least 20k less context 
switches and 20k less messages.

Regards,
Paulo



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