when rebooting the Pi4 Controller

[Ciprian Manea]

• Controller Pi can be rebooted without interrupting power to Pi Zeros, network recovers on boot (not available when using a Pi4 controller).

Hi there,

Is this above problem solved in the latest ClusterHAT v2.4 hardware? 🤔

[just double checking]

Thanks,

Ciprian

[Chris Burton]

Hi, 

• Controller Pi can be rebooted without interrupting power to Pi Zeros, network recovers on boot (not available when using a Pi4 controller).

Hi there,

Is this above problem solved in the latest ClusterHAT v2.4 hardware? 🤔

Yes, on v2.4 the i2c expander is no longer powered using the 3v3 from GPIO so it doesn't reset when a Pi4 reboots.

Chris.

[Ciprian Manea]

Yay! 🖖🏻

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[Eythymios Iosifidis]

Hello!

I would like to ask if having a Pi4 as a controller provides a real benefit compared to a rpi 3B+.

Thank you!

Best Regards,

Efthimis

Τη Παρασκευή, 20 Μαρτίου 2020 - 5:25:54 μ.μ. UTC+2, ο χρήστης Ciprian Manea έγραψε:

Yay! 🖖🏻

On Fri 20. Mar 2020 at 17.19, Chris Burton <bur...@gmail.com> wrote:

Hi, 

• Controller Pi can be rebooted without interrupting power to Pi Zeros, network recovers on boot (not available when using a Pi4 controller).

Hi there,

Is this above problem solved in the latest ClusterHAT v2.4 hardware? 🤔

Yes, on v2.4 the i2c expander is no longer powered using the 3v3 from GPIO so it doesn't reset when a Pi4 reboots.

Chris.

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[Ciprian Manea]

RPi 3B+ is limited to 300Mbps over all USB interfaces plus Ethernet, as the bus is shared and USB interfaces are all 2.0

RPi 4B has 1 Gbit Ethernet interface, plus 2x USB 3.0 ports, and they won’t share a bus 😎

But, I’m not sure if the serial microUSB to USB cable provided with ClusterHAT v2.2 hardware is USB 3.0, looks too thin for it (maybe 2.0?), but then you’re left to consider/wonder how much the USB circuit on the ClusterHAT v2.2 or (latest) v2.4 can do in Mbps? I guess circuits for USB 2.0 are cheaper / easier to implement.

I tested ClusterHAT v2.2 on a Raspberry Pi 3B+ controller, and indeed the Zero’s won’t push above 300Mbps together (each was pushing below 100Mbps)

As you can see in the above picture, there isn’t much room left in USB2.0 to push with, even when you have RPi 4B (unless the ClusterHAT is USB3.0 🤓)

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[Chris Burton]

Hi,  

I would like to ask if having a Pi4 as a controller provides a real benefit compared to a rpi 3B+.

 Other than taking any Ethernet traffic off the USB port and obviously being faster itself not much I can think of atm and if you have a Cluster HAT v1.x-v2.3 you'd lose the ability to reboot the controller without it powering off the Pi Zeros.

 

As you can see in the above picture, there isn’t much room left in USB2.0 to push with, even when you have RPi 4B (unless the ClusterHAT is USB3.0 🤓)

Using a USB 3 hub wouldn't make any difference as the USB Gadget capable interface on Pi Zero/A+/3A/4B  are only USB 2.

Chris.

[Ciprian Manea]

okay, so the advantage of RPi 4B controller vs RPi 3B+ is a theoretical 480Mbps transfer between itself and all the Zero’s, vs 300Mbps (for RPi 3B+ and its Zero’s)

Thanks for the details re: USB (2.0) Gadget mode 🤓

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[Ciprian Manea]

Just a note, and a changed subject

RPi 3B+ with k3s server plus k3s agents on all Zero’s reduces the (CPU, thus) network speed to maybe around 35 Mbps per Zero (with all 4 in use)

Down from about 75 Mbps x 3 Zero’s when k3s is off all the way (or a clean ClusterHAT), as one of the Zero's will be completely bottlenecked (by the RPI 3B+ kernel’s IRQ serving on only one core: you’ll see it easily in htop eating all it can on core #1; anyone knows if/how kernel’s IRQ can be balanced/shared between more cores? 🤔)

OH, I pinned each iperf3 -s on cores 2,3,4 for each remaining Zero, so I can easily see core #1

AND, the real kicker is RPi 4B as Controller (hot from the test bench)

all 4 Zero’s are pushing their metal with 60 Mbps each, core #1 in 4B is at 75%, all the other 3 cores are in 10-15% usage range; kernel’s IRQ handling on core #1 is just about 15% (but the os/sys is still eating 50% — in other things I didn’t dig too much into)

(personal) NOTE: I bought a few Banana Pi M2 Zero’s to try them out — yeah, 4 cores each; and I have one quick advice: don NOT buy them for ClusterHATs! The [M2 Zero] unit I tested heats up to 75 degrees Celsius in no time, then it lowers the CPU clock to — dead, or the CPU gets halted (no message on screen) for being too hot. You can’t attach a heatsink to them as they’re already on a more crowded PCB than RPi Zero, plus there’s no such space in the ClusterHAT quad-scuit for heatsinks. I guess water cooling is not an option 😊 and air cooling — hmm, what case & fans can cool 4x of them when tightly coupled in a ClusterHAT quad-scuit?🤔