[SR-Users] async workers

[Vitaliy Aleksandrov]

>>> Hi,
>>>
>>> What is the practical limit to the number of async worker processes?
>>>
>>> With SIP child processes, it seems to be about the number of available
>>> CPUs in /proc/cpuinfo. After that--at least, per my testing--one
>>> begins to hit the point of diminishing returns, presumably due to SHM
>>> IPC and synchronisation issues.
>>>
>>> Is the restriction similar in the async execution context?
>> no specific restriction. Also, I haven't seen any degradation when using
>> more sip worker processes that cpus, which I do have always (at least 2
>> per CPU), because a worker can do quite a lot of I/O.
>
> I have seen such degradation, at least in my VM testing environment. I 
> find that I get the highest CPS (e.g. with sipp) with the smallest 
> number of workers.
>
> Actually, I get as good throughput with 4 workers (in an 8 "CPU" 
> scenario on a quad-core processor) as I do with 8! Increasing beyond 8 
> leads to diminishing returns.
>
With real traffic some of workers can be busy on blocking operations 
such as database queries or host name resolution. So I prefer to add 
more workers to not get in situation when all my workers are blocked by 
something.