[OpenSIPS-Users] OpenSIPS maximum performance in a multiprocessor machine (SMP)

[Bogdan-Andrei Iancu]

Italo Dacosta wrote:
>> Ok - that's the first problem. Number of children == number of
>> processes. You cannot handle more than 4 messages at one time right
>> now.
>>     
>
> I forgot to mention that I tested with several number of children
> already. Surprisingly, increasing the number of processes seems to
> reduce performance. With 8 children processes the maximum call rate I
> measured was around 17,000 cps. I think that the performance is lower
> due to the overheads associated with context switching.
>   
Here there is a whole theory.

Starting first with the concept of parallel computation: ideally you 
assume an application has an 100% of parallelism (if you have a core, 
you get a performance of N, if you have X cores, you get a performance 
of X*N) - in reality, most of the application have a much lower degree 
of parallelism, mainly due shared data, access on common resources 
(sockets), synchronization between processes, etc .

So, the first conclusion we can have is that, for an ideal application, 
it is enough to have to a number of procs equal with the number of cores 
you have on the machine.


Now, second part is about the CPU computation ops via I/O blocking ops - 
the above conclusion is correct as time as the application is doing pure 
computation (no I/O). Once the app starts doing I/O, you have wait time 
in kernel, rescheduling - more or less "dead time" from your application 
point of view. In practice, this "dead time" can be compensated by a 
higher number of processes. For ex. while a process is blocked in doing 
some DB I/O, and blocking DNS query, etc, another process may use the 
CPU and do some non-I/O ops.

So, the second conclusion is that you should increase the number of 
procs directly proportional with the degree of I/Os performed by your app.



In your particular case, the I/O delay is low - you do not use DNS, no 
DB module, etc - only I/O is on the network sockets where the sharing of 
these sockets between the procs is done by kernel.

Regards,
Bogdan