[asterisk-dev] Dahdi resource limit

[Shaun Ruffell]

On Tue, Apr 03, 2012 at 06:22:36PM +0200, Olle E. Johansson wrote:
> 
> 3 apr 2012 kl. 17:01 skrev Shaun Ruffell:
> 
> > On Tue, Apr 03, 2012 at 10:18:22AM +0200, Olle E. Johansson wrote:
> >> 
> >> I am lost how to debug this and provide a good report. Dahdi
> >> developers - are you aware of some sort of limit apart from the
> >> file handles that can lead to this issue?
> > 
> > 2.5.0 was the first release to add a module parameter to specify the
> > maximum number of psuedo channels that can be opened (and lowered
> > limit from hard coded 1024 for all channels to 512 for only pseudo
> > channels). Perhaps your bumping into that? 
> > 
> > The change went in in r9610 "dahdi: Add module parameter to limit
> > number of pseudo channels." [1]
> > 
> > [1] http://svnview.digium.com/svn/dahdi?view=revision&revision=9610
> 
> Thanks for the feedback, Shaun!
> 
> As I wrote before - we have configured Dahdi to for 4000 file handles,
> but still hit some kind of limit around 1400 open ones.

Ahh, I wasn't exactly sure what you meant by "we have configured
Dahdi for 4000 file handles".  The 'max_pseudo_channels' only limits
the total number of psuedo channels that can be created, not the
total number of open descriptors to DAHDI objects.

So regarding your original question about what limits may be in the
driver: There is a hard coded limit of 1024 conferences which you
may be hitting if you're dropping each psuedo you create into it's
own conference. See DAHDI_MAX_CONF include/dahdi/user.h if you want
to bump it up, but I still think you should be CPU bound before you
hit that limit.

Since all the conferencing is done on a single CPU, I can't open
more than about 1500 psuedo channels and still have a usable system.
Too much time is eaten up in the context of the timer interrupt
which is handling all the mixing, transmit, and receives for those
pseudo channels.

Try the following to get a sense of how many psuedo channels you
might be able to open:

 # /etc/init.d/dahdi stop
 # modprobe dahdi max_pseudo_channels=4000
 # ulimit -n 4000

Then run the following through your python interpreter:

  import sys
  import time
  
  chans = []
  x = 0
  
  while True:
      chans.append(file("/dev/dahdi/pseudo", "rw"))
      time.sleep(0.01)
      x = x + 1
      sys.stdout.write("%d " % (x))
      sys.stdout.flush()

When the CPU that is running the timer gets pegged out, this process
can take awhile to kill, but everything will go back to normal once
it is.

The load on the system is even more pronounced when those pseudos
are actually in conference with one another.

Does this help?
Shaun

-- 
Shaun Ruffell
Digium, Inc. | Linux Kernel Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at: www.digium.com & www.asterisk.org