[time-nuts] Comparing the BeagleBone Black & Raspberry Pi asNTP servers

Wolfgang Wallner wolfgang-wallner at gmx.at
Sun Mar 22 18:01:52 EDT 2015

What kernel do you use? And what scheduling configuration?

As it is a timing application, and sensible to jitter, I would suggest
to use a real-time kernel (e.g. Preempt RT) [1].

Usually one can find pre-built kernels with PreempRT-support for boards
like the RPi etc. on the internet.

If you use a real-time kernel, and have it configured that your
application of choice (in this case ntp) has real-time priority, the 16%
cpu usage won't be a problem any more. Other workloads like IRQs or task
scheduling may have much worse effects on application jitter (even on
real-time systems).

Interestingly, more CPU usage can even be better for jitter-sensitive
applications: low cpu usage might enable power-saving functions, which
in turn might lead to longer reaction times once an application needs to
be handled.

regards, Wolfgang

[1] https://www.osadl.org/Realtime-Linux.projects-realtime-linux.0.html

On 03/22/2015 08:46 AM, David J Taylor wrote:
> David:
> On the BBB, were you running the fully loaded release, or the minimum
> "console" version of the OS?
> Which specific version of the OS?
> Thanks,
> --- Graham
> =================================
> Graham,
> The download was:
>  bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img.xz  (547,024,548 bytes)
> which was from the "Recommended Debian Images" from:
> http://beagleboard.org/latest-images.  Perhaps there are some services
> or background tasks I can disable to reduce the CPU steady load from its
> present 16% average level?
> 73,
> David GM8ARV

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