[asterisk-users] Terrible dahdi_test results

[Mike Leddy]

Thanks again Russ,

Just a quick reply for now.

No virtualization, but yes I am running a tickless kernel:

#
# Processor type and features
#
CONFIG_NO_HZ=y

Standard for debian kernels. I booted with nohz=off and the behaviour
changed. Unfortunately for the worse:

# dahdi_test 
Opened pseudo dahdi interface, measuring accuracy...
66.653% 66.683% 66.683% 66.807% 67.705% 66.666% 66.651% 66.679% 
67.516% 66.882% 66.649% 66.657% 66.678% 66.668% 66.672% 66.664% 
66.675% 66.675% 66.659% 66.692% 66.631% 66.187% 66.650% 66.710% 
66.648% 66.633% 66.714% 66.638% 66.688% 66.794% 66.645% 66.696%
--- Results after 32 passes ---
Best: 67.705% -- Worst: 66.187% -- Average: 66.726523%

Comparing the boot messages without nohz=off:

[    0.000000] hpet clockevent registered
[    0.000000] Fast TSC calibration failed
[    0.000000] TSC: Unable to calibrate against PIT
[    0.000000] TSC: using HPET reference calibration
[    0.000000] Detected 2593.456 MHz processor.

and with nohz=off:

[    0.000000] hpet clockevent registered
[    0.000000] Fast TSC calibration using PIT
[    0.000000] Detected 2593.225 MHz processor.

I am encouraged that we seem to be homing in on the problem. I need to
read up a bit more on the subject.... and look at possible power 
saving issues on this machine.

Best regards,

Mike


On Tue, 2014-05-13 at 15:26 -0500, Russ Meyerriecks wrote:
> On Tue, May 13, 2014 at 7:28 AM, Mike Leddy <mike at loop.com.br> wrote:
>         But on examination the /etc/init.d/dahdi start was only
>         loading
>         the dahdi module.
> 
> 
> With this in mind I might start looking around the system for things
> which might cause jitter in the servicing of system timer interrupts:
> 
> 
> Are you running under a virtualized environment?
> Are you running a tickless kernel? (maybe try adding nohz=off to your
> kernel boot parameters)
> Is there some sort of processor power saving or frequency scaling
> going on that interrupts the system timer?
> 
> 
> -- 
> Russ Meyerriecks
> Digium, Inc. | Linux Kernel Developer
> 445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
> direct: +1 256-428-6025
> Check us out at: www.digium.com & www.asterisk.org