Hello Bryan,
Here are my thoughts (and not directly related to Collectd itself): Java
is fast, but the JVM will require a good amount of memory, which you
might not have plenty your "little SOC".
If the Java program is not running continuosly, starting the JVM
everytime is not an option for you. C would definitely be a better
option for it. And also help with memory consumption (you definetely
don't need OOP or all Java features to get this work done).
--
Alceu
Em 15/06/2017 14:27, Bryan Varner escreveu:
Hi all,
I have a feeling I know what the answer to this question will be, but I wanted
to ask here in case someone has a better or easier idea....
I have an i2c sensor that I can poll with libsensors (and the appropriate collectd
plugin). I'd like to read this value > 60 times a second, then calculate the
RMS of the value and log _that_.
So far, I've tried using the sensors plugin with it's own ridiculously small
interval, and a custom filter & read plugin that would cache the values
dispatched to it, then when it's read interval hit, would do the calculation on the
cached data points and dispatch the result.
This resulted in the sensor plugin read not being 'fast enough' to get enough
samples / interval for the calculation to be anywhere near accurate.
I have a sneaking suspicion that because my filter / coalesce plugin was in
java, the context swaps were just too much for the little SOC (it's a Raspberry
Pi Zero W) I'm running all this on.
So I guess I'm trying to figure out what path to take at this point:
* Should I bail on the filter / read plugin approach completely and write my
own purpose-designed plugin?
I'm thinking something that creates a high-priority thread to read the
sensor data into a circular memory buffer then on 'read' intervals does the
calculation and reports the results?
I think this would make more sense, but is there a 'right way' or 'wrong
way' to handle threading in a collectd plugin?
* Or is it possible that the JVM overhead was just too much for the SOC and I
should reimplement the filter / coalesce read as a generic C plugin instead of
Java?
* Is there a simpler method I'm just missing?
Regards,
-Bryan
P.S. Yes, I realize I'm trying to aggregate / calculate a value, but that's the
value I want reported to my storage backend, the other minute values are really
useless without the calculation, and I'd rather calculate the rolling RMS upon
collection (and store a meaningful number) rather than calculate it for every
reporting cycle later.
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