lerner
Posts: 509
Joined: Sun Mar 29, 2015 12:12 am

RPI 3 load confusion (and RPI2)

Thu Feb 07, 2019 7:08 am

I have this situation where I have an old RPI 2.

aka "TimePi"

Code: Select all

Raspberry Pi Model B Rev 2

PRETTY_NAME="Raspbian GNU/Linux 9 (stretch)"
NAME="Raspbian GNU/Linux"
VERSION_ID="9"
VERSION="9 (stretch)"
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"

Raspberry Pi reference 2018-03-13
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 00013d7972122d1304aacda8fff5098f073ceb43, stage5
I get that for what it is and what it is doing, the load is high.

The other pictures is on the next post.


Doing the command `top` I see a list and a quick look I see the big loads at the top and as I look down the screen the processor load reduces.

On my RPI 3

Aka "TelePi"

Code: Select all

Raspberry Pi Zero W Rev 1.1

PRETTY_NAME="Raspbian GNU/Linux 9 (stretch)"
NAME="Raspbian GNU/Linux"
VERSION_ID="9"
VERSION="9 (stretch)"
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"

Raspberry Pi reference 2017-09-07
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 496e41575eeb9fa13f394ffb407b7bc1d00b21c2, stage5
It is showing a high load and when I do the `top` command, I don't really see where the load is.

Both are running Node-Red.

On the RPI 2, Node-Red is taking about 50% of the load where the total load is varying between 50 and 100%.
But, I can see the "Node-Red" listed at the top.

The 3 is also running a high total load (which is weird in ways) and when I do `top` Node-Red is showing about 20%.

Could someone help me learn more about what I am seeing?

Here are two screen shots showing what I see. Look at the red highlights.
Attachments
Screenshot from 2019-02-07 18-09-44 2.png
Screenshot from 2019-02-07 18-09-44 2.png (204.39 KiB) Viewed 448 times

lerner
Posts: 509
Joined: Sun Mar 29, 2015 12:12 am

Re: RPI 3 load confusion (and RPI2)

Thu Feb 07, 2019 7:25 am

The second screen shot.

This is "TimePi" and the one which I do understand.
Attachments
Screenshot from 2019-02-07 18-09-48 2.png
Screenshot from 2019-02-07 18-09-48 2.png (206.06 KiB) Viewed 447 times

jahboater
Posts: 5209
Joined: Wed Feb 04, 2015 6:38 pm
Location: West Dorset

Re: RPI 3 load confusion (and RPI2)

Thu Feb 07, 2019 8:07 am

The second pi "TelePi" is a Pi Zero, not a Pi3.

The Pi Zero is a low powered single core ARMv6 cpu - it is much slower than a Pi2.

lerner
Posts: 509
Joined: Sun Mar 29, 2015 12:12 am

Re: RPI 3 load confusion (and RPI2)

Thu Feb 07, 2019 10:05 am

Thanks.

Not having a go at you for the reply.

That makes sense, but I can't reckon the values from the top command.
On TimePi - the RPI2 - I see the column of CPU load and I can see the total makes sense.

Looking at the Zero's column, the gauge is showing 100% load, but the column total is way short.

How does that column get to 100% when I can't see enough entries?

That's what is confusing me more than the lower powered processor.

jahboater
Posts: 5209
Joined: Wed Feb 04, 2015 6:38 pm
Location: West Dorset

Re: RPI 3 load confusion (and RPI2)

Thu Feb 07, 2019 10:33 am

Maybe there are discrepancies between the measuring software.

The CPU load may be rapidly changing all the time.

Your "remote" monitoring software has to poll each of nine machines.
I don't know how it does it - is there an "agent" running on each host or maybe its just using ssh to look at /proc/stat or something.
I don't know how frequently it does the poll (maybe make top update at the same rate that your other software polls).
top is frequently monitoring the local machine only.

Note also that the Pi Zero is single core, but the others (Pi2 and Pi3) are quad cores.
When you are talking about "total" load on the machine, different software interprets that in different ways.

The Pi Zero is very slow and the monitoring software itself may impose a significant load. The others are faster and may have spare CPU cores to execute the monitoring software in, giving more predictable results.

lerner
Posts: 509
Joined: Sun Mar 29, 2015 12:12 am

Re: RPI 3 load confusion (and RPI2)

Thu Feb 07, 2019 7:45 pm

Thanks

That may explain it.

Return to “Troubleshooting”