9th of November

USB charging
The Comsol USB charger that I wrote about in my last post turned out to be a dud. After about 24 hours I found that it had stopped one of the fans on top of the Pi^4 case and was trying to power off one of the Pi3B+ nodes. Clearly its designed for charging rather than providing constant power. I have put back the Astrotek USB charger which got all 4 Pis and the fans running. This is one of the drawbacks of using USB chargers, most of them aren’t designed to supply constant power.


An experiment
I thought I would try a couple of the Pis running just 3 tasks at a time instead of the usual 4 to see if it was any quicker. The short answer is yes. The longer answer is yes its quicker but not by enough.

After averaging out the run times the couple of Pis that ran 3 tasks came in about 15% quicker than those that ran 4 at a time. That isn’t enough to make up for the 4th core. The testing was on Pi3B+ nodes running the Einstein BRP4 work units which typically take 11 hours and 10 minutes (per task) when running 4 at a time. I haven't tried the Pi4 - It could give totally different results.


Aarch64
It seems the Raspberry Pi foundation have an experimental 64 bit kernel available that they’re testing, particularly on the Pi4 but the Pi3’s can also run it. There have been reports of issues getting it to run 32 bit apps (the armhf architecture) over at Einstein.

Ubuntu have also said they are going to support the Pi4 from Ubuntu 19.10 onwards. They also have noted a kernel bug where the USB stops working on the 4GB Pi4. Their work around is to tell the Pi it only has 3GB of memory until they can get the kernel patched.