[asterisk-dev] rtp scalability improvement...

[Luigi Rizzo]

On Mon, Mar 20, 2006 at 04:03:26PM +0600, Paul Cadach wrote:
> Hello,
> 
> Roy Sigurd Karlsbakk wrote:
> [skipped]
> > These IRQ storms are only happening on crappy network hardware. My
> > testing was one with intel gigabit NICs with large buffers,
> > effectively producing < 100 interrupts per second. kernel profiling
> > showed time was indeed spent in system calls
> 
> The one solution I see is to move RTP _switching_ into the kernel level (like
> zaptel conferencing doing), and optimize Asterisk core to do better codec
> selection logic (i.e. to always minimize/eliminate transcoding when it is
> possible).

Transcoding is expensive but has no relation to system calls load.
I went to look what syscall rates are sustainable by a modern box and
a random result from google says this:
http://marc.theaimsgroup.com/?l=linux-kernel&m=103942289025149&w=2

so it's over 200k syscalls per second. I doubt the 40k pps may
account for more than 10-20% of the total system time spent,
so the suggested idea of mmapping packets won't help.

There are many other expensive things e.g. i would look into
lock/unlock calls (depending on which thread package you have,
those can be very expensive).
Hard to tell without an indication on how many syscalls per second
the original poster (Roy ?) was seeing, how many pps, and which
type of syscalls were involved.

	cheers
	luigi