Hi, I have an RPi5 running only boinc, a mix of projects - asteroids , einstein, with a bit of TN-grid when it has work. It's mostly runs fine but once in a while asteroids will cause the machine to get extremely hot i.e 85 degrees. The RPi has a large heatsink above and below the board and under no load runs at around 34 degrees , and for all einstein,TN-grid and *most* asteroids, stays below 75 degrees.

However every few weeks it seems I get asteroid workloads that push the heat up significantly i.e a further 10 degrees. I have tried to use preferences to restrict the amount of CPU on the RPi5, but changing this and issuing a boinccmd update appears to be ignored, as does restarting the service. So for the time being I have paused the machine running asteroids until I find a solution.

the processor is
ARM
[Impl 0x41 Arch 8 Variant 0x4 Part 0xd0b Rev 1]

the OS is Linux Debian
Debian GNU/Linux 12 (bookworm) [6.6.31+rpt-rpi-2712|libc 2.36]

An example of one of the workunits with this characteristic ,had the name ps_240826_input_49170_72_1

The machine is dedicated to boinc, is headless and has no gui running.

a companion Rpi3 runs asteroids fine all the time and never gets above 65 degrees even with overclocking and tiny stick on heatsinks

Why would some work units raise the CPU temperature so much ?

One apparently unrelated thing I noticed which might shed some light is when I got the RPi 5 I mistakenly installed a 32bit version of the OS, and this had terrible problems with overheating with boinc, until I realised and went 64bit, after which everything run a lot cooler. Could some work units be using 32bit code ?

two things:

the rpi5 can use the NEON SIMD optimizations, which work the CPU harder. your rpi3 tasks are not using this. I'm not sure if that's a limitation of the 32-bit app or the specific implementation of NEON SIMD with the asteroids app with armv7.

the other factor is that the rpi5 runs at like twice the clock speed of a rpi3. which generates more heat.

the asteroids app does generate more heat than other projects from my experience, this is normal due to the SIMD optimizations. my rpi5 does see fairly high temps at about 75C running asteroids. you said you have a heatsink on it, but do you have a fan on it too? you'll probably need some airflow over it.

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Thank you for your reply, which clarifies a number of things.

The heat sink I have is a combined heatsink and case and has quite a substantial aluminium vanes across the top and bottom on 80% of the card. It doesn't have fans as I find the noise intrusive and try and achieve passive cooling, so a big heatsink and sat on a large flat piece of granite .I monitor the temperature using vcgencmd measure_temp

The thing is most of the time the RPi5 can run 4 cores of asteroids 24x7 and not exceed 70 degrees. I've left it like that for days and it's quite comfortable. But sometimes it seems to go 10 degrees higher., and I can't figure out why . perhaps it slowly drifts into an upper temperature range and thermal cpu throttling means that we end up not clearing the WU and never lowering the temperature ?


Are the WU all similar in demands on the processor ?
Would all WU's exercise the NEO SIMD optimization that you mention ?

That certainly accounts for why the RPi never gets above 62 C

Thank you

There is a bit of variability in the work units. Some are configured to do more work than others. So those ones will exercise the cpu harder and longer.

You are running the 'universal' 102.20 cpu app which always uses the most efficient and highest level SIMD instruction set the cpu supports which is Neon in your case.

The easiest solution would be to put a fan on the case. There are many fan options which are quiet.

I have no issues with the asteroids work units on my Pi5. I have a fan/heatsink on it and can't hear it.

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A proud member of the OFA (Old Farts Association)

Thank you