[asterisk-users] Dahdi_dummy is more accurate than core timer?

[Gareth Blades]

On 02/10/13 12:17, Johan Wilfer wrote:
> Hi,
>
> I have some servers that are dedicated to do meetme conferencing. From 
> some previous test i concluded that I need to use dahdi_dummy as it is 
> more accurate.
>
> If I did use the core timers in dahdi (not loading dahdi_dummy) I got 
> bad quality in the conferences and dahdi_test showed 99.6% as worst.
>
> I thought maybe the issue as bad hardware for the timing or something 
> else. But today I re-ran these tests on another server showing the 
> same thing.
>
> - Can anybody comment on why DAHDI with core timers drop down to 99.6% 
> occasionally?
> - Is a hardware-card for timing the most efficient way to get timing 
> even if I just use the card for the timing?
>
>

Its a little different when you are using meetme as its an application 
built into dahdi itself and not a native asterisk application. It will 
therefore always use dahdi for its timing. If dahdi doesnt have a 
hardware interface (sangoma sell a usb based timing source if you want a 
hardware source) then it will use a software timing source of some form. 
I dont know what method it uses.

Asterisk itself will use dahdi for timing but if res_timerfd is 
available it will use that itself. With your kernel version timerfd 
should be available.
So if you run the following command asterisk will perform 1024 ticks 
over 1000ms which is equivalent to the dahdi test of 8192 over 8000ms 
(if you run it a few times). You can see in my case asterisk is using 
timerfd and no issues at all with the timing.

 > timing test 1024
Attempting to test a timer with 1024 ticks per second.
Using the 'timerfd' timing module for this test.
It has been 1000 milliseconds, and we got 1024 timer ticks

We are developing a conferencing feature and rather than use meetme with 
its dahdi requirement we are using confbridge10 instead so we dont have 
to have dahdi installed and it will use the better timerfd timing source.

More information about timing sources can be found at :-
https://wiki.asterisk.org/wiki/display/AST/Timing+Interfaces