Connection lost in Raspberry PI Zero W

Hardware
1

Hello Guys
I am working on large node-red project in Raspberry PI Zero W.
That project contains over 1900 nodes and MQTT communication with C application.
But I see connection lost almost of time.
Also I have many 'time interval' nodes, but real time interval is irregular.

I tested it on RPI4, it works well without any connection lost and I can see regular time interval in same node-red flow.
I need to implement this project on RPI zero W.
Following is CPU usage on RPI zero W.

 PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
  258 daytech   25   5  343200 241920  26368 R  77.8  54.6  66:08.55 node-red
  993 root      20   0   19220   1928   1688 S  17.4   0.4   6:16.56 i2c_publisher
 1024 daytech   20   0   10184   3044   2560 R   1.9   0.7   0:35.83 top
 1059 root      20   0       0      0      0 I   1.3   0.0   0:01.32 kworker/0:2-events_power_efficient
  896 daytech   20   0   12856   4540   3204 S   0.6   1.0   0:05.20 sshd
 1010 daytech   20   0   12188   4212   3432 S   0.6   1.0   0:07.36 sshd
    7 root      20   0       0      0      0 S   0.3   0.0   0:36.22 ksoftirqd/0
  128 root      20   0       0      0      0 S   0.3   0.0   1:35.25 spi0
  277 avahi     20   0    5888   2888   2572 S   0.3   0.7   0:07.47 avahi-daemon
  300 root      20   0   27640   1344   1216 S   0.3   0.3   0:05.08 rngd
 1025 root      20   0       0      0      0 I   0.3   0.0   0:20.38 kworker/0:1-events
    1 root      20   0   33564   7600   6228 S   0.0   1.7   0:09.07 systemd
    2 root      20   0       0      0      0 S   0.0   0.0   0:00.01 kthreadd

Can you help me for it?

Thank you.

2

If that is a typical output from top then it is unlikely to work as you are at 78% cpu and 55% memory just for Node-RED. Usually you should be aiming for less than 10% . As we have no idea what you flow is trying to do - all we can suggest is that you do less of it... either less scale (fewer nodes) or less speed (fewer messages) or less complex (again fewer nodes).

3

Hello dceejay
Thank you for your reply.
I have noticed when number of interval nodes is reduced, the frequency of it's connection lost is low a bit.
But time interval is still irregular.

Is there not the solution for resolving this issue?

Thank you.

4

So it runs fine on a Pi4 - an ARM v8, 1.5 GHz, 1GB, 2GB or 4GB machine (you didn't specify) but not so well on the Pi Zero W - an ARM1176, 1GHz, 512MB machine, or to put it another way, it works on the fast machine, but not the one that has half (or 1/4 or 1/8) the memory and runs 1/3 slower.

I would suggest that you try optimizing your flow as @dceejay suggested

5

Hello Zenofmud
Thank you for your reply.
I have just found the interested thing.
Once I removed "Aedes MQTT broker" node in node-red flow, there is no connection lost.
But CPU's usage is still 60%.

MQTT communication between node-red and C application is issue?

6

Well if you removed the MQTT, you are not getting msg's from it so you have reduced the load on the Pi.

Where were you seeing the 'connection lost' message? in the editor? in the dashboard?

7

I am seeing "connection lost" at top right on dashboard.

8

Well I would guess that remving the MQTT datta comng in reduced the load on the Pi Zero W allowing it to keep up the connection to the dashboard.

So now you are left with a choice - keep MQTT off or run it on a more powerful Pi.

9

Are you running/viewing the dashboard on the pi 0 as well. It would be better to use a browser on a different machine.

10

I am connecting to RPI on other machine.

11

Hello Zenofmud and dceejay
Thank you for your reply
I need your help for data exchange between C application and node-red.
I read the data from I2C slave in C application and then published to node-red using MQTT on current solution.
But this has some issue on connection, as you knew.
Before I use MQTT, I used file operation for it, but it missed some data because read/write synchronization.
The data received from I2C data need to be processed within 30ms at least.

Besides of MQTT or file operation, what method can I use for my application?

Best regards.

XiaoBin.

12

What makes you think that the problem is with MQTT?

There is no way on a pi zero running Raspbian that you will be able to guarantee 30ms action. It is not a real time operating system and sometimes it will be busy doing other things for longer than that.

13

Thank you Colin.
If time is 100ms, is it possible?

14

There is no answer to that question because it depends on what else is going on, and what you mean by 'possible'. As I said, Raspbian (based on Debian) is not a Real Time OS, so nothing is guaranteed. I the Pi is not heavily loaded (I suspect yours is heavily loaded) then usually response would be better than 10ms I think, but occasionally it may go away for large fractions of a second, or even more. There is no way of knowing whether it is good enough for your requirement other than trying it.

15

Hello Colin
That's good.
I want the stable communication between C application and Node-RED without connection lost.

16

As has already been pointed out if the processor is working 100% then it is unlikely to work well.

17

Can you explain some more about your use case? For example you mention it runs fine on a pi4, but it has to run on a pi0. Why does it need to run on that pi0 specifically? Since it has far fewer capabilities than the other pi models, what you’re doing here (you mentioned a huge number of nodes in your opening post), might simply be too heavy to run on a pi0. What part of your use case makes it so important it runs on that, and would it be possible to delegate tasks instead?

I use a pi0w myself to test parts of flows for performance occasionally. If it still runs moderately smooth on it they’re good to go. But once you feel the delays in seconds, not just milliseconds, things have to be changed.

18

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