[OpenSIPS-Devel] RFC: new opensips design

[Dan Pascu]

On Friday 07 November 2008, Stefan Sayer wrote:
> nowadays, thread creation has become so cheap (in comparision...), that
> synchronous MT (create one thread per task) is definitely an option I
> would say.

I would say the contrary. Linux, which is the most likely platform to be 
used, uses the same system call to create a thread or a process (in fact 
threads are just a particular case of a process in linux). Thus the myth 
that threads are "lightweight" compared to processes is just that (at 
least in linux' case). Also as I mentioned before, it's not just thread 
creation that counts, it's context switching as well. I've seen 
benchmarks (unfortunately I no longer recall the URL), where with a few 
thousands of threads, context switching was using more CPU than the 
application itself.

I've also seen benchmarks (again I don't remember the URL), where an async 
based web server implementation would scale linearly with the number of 
requests, while the equivalent multithreaded version which attempted to 
create a thread per request was going down after a certain number of 
requests per second exactly because of the context switching penalty 
mentioned before.

-- 
Dan