[Freeswitch-users] centos 5.4 timer issue 1000hz, choppy voice at times

[Anthony Minessale]

2-3 is fine.
but the problem is when it's actually put to the test in userspace where you
have many threads competing for cpu, that is where you have to measure the
accuracy which is what that test during startup is doing.  using FS to sleep
1000 microseconds and timing how close it actually is to that.

voip can withstand jitter on most implementation as long as the running
average of the packets is on the mark, the timing of each individual packet
is less important, this worsens over latent connections.

try this from the cli

time_test 1000

you will see it come out + or - 100 easily (there is overhead for the code
executing as well as other factors  that can skew the results)

then try it with a larger sample:

time_test 1000 1000
time_test 1000 2000
etc

the more times you try it the more likely the average in the long run will
be accurate which is all we can hope for in our pseudo real time
environment.

most times if you try this with -nocal you will always get 2000 when you
intended for 1000
which means all your 1ms sleeps are double length from what was requested.

some newer kernels try to make it more accurate but by doing so they eat up
so much cpu it's not worth it.  For the most part semi-accurate 1ms timing
is more than enough.







On Tue, May 18, 2010 at 1:47 PM, Joseph L. Casale <jcasale at activenetwerx.com
> wrote:

> >[root at pum2 ~]# ./timerchk
> >kernel timer interrupt frequency is approx. 1002 Hz
>
> So Anthony,
> What is the expected safe deviation fs would operate in where any
> audio issues I could assume would not be related to a shady clock.
>
> On a variety of platforms I see 2-3 Hz variation but only on some
> does fs complain. Or could it be that this deviation alone isn't
> enough to quantify the quality of the clock?
>
> Thanks for any input!
> jlc
>
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-- 
Anthony Minessale II

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