[Asterisk-Users] real-time priority , -p switch

[Peter Svensson]

On Thu, 11 Aug 2005, Joseph wrote:

> In this case could somebody explain to me why run asterisk with ''-p"
> switch?
> According to "asterisk man" explanation for -p is as follow:
> 
> "If supported by the operating system (and executing as root), attempt
> to
> run with realtime  priority for  increased  performance  and
> responsiveness within the Asterisk process, at the expense of other
> programs running on the same machine."
> 
> Since Linux is not RTOS, why some folks are using this "-p" switch?
> It has no effect on standard Linux box.

Linux is not a hard realtime os with guaranteed timing. What the -p flag 
does is to request the realtime scheduler. This means a process wil no 
longer be subjected to the stanadrd unix scheduling but rather use a 
strict priority scheduling. The net result is that once a process using 
the realtime scheduler is ready to run the kernel wihh schedule it as soon 
as possible. It will only be preempted by realtime processes of the same 
or better priority.

With the addition of the lowlatency patches the worst case latency for 
userspace applications is very low. The remaining difference between a 
hard RT os is the guarantees it can make.

Peter