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#1 2021-11-04 09:07:09

vanfanel
Member
Registered: 2021-10-27
Posts: 3  

Video turns off on high CPU usage with Devuan 4.0 on Raspberry PI 4

Hi there,

I successfully run Devuan 4.0 arm64 on a Pi4b, but HDMI screen turns off and never comes back when all 4 cores are used for long compilation tasks. The screen goes off and never comes back.

Note that I use the full KMS graphics stack, so in config.txt I have:

dtoverlay=vc4-kms-v3d

And in cmdline.txt I have:

video="HDMI-A-1:1280x720@60"

Note that all hdmi_* config options are ignored in full KMS mode, since it uses the standard Linux KMS interface instead of the Broadcom-propietary video interface that those hdmi_* options are for.

This bug also happened on Raspberry Pi OS at some point, but it was eventually fixed:

https://github.com/raspberrypi/firmware/issues/1598

It has to do with throttling: throttling is happening, but it shouldn't cause video to be disconnected.

Also, is there a Pi4 arm64 kernel package I can update via apt-get? The image comes with a custom PREEMPT kernel, which is great, but I don't know how to update the kernel or the firmware (dtbs, etc).

Thanks!

Last edited by vanfanel (2021-11-04 12:30:34)

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#2 2021-11-04 12:59:13

ShorTie
Member
Registered: 2020-05-14
Posts: 21  

Re: Video turns off on high CPU usage with Devuan 4.0 on Raspberry PI 4

If you fix your heat/thermal problem so no throttling occurs.
With a simple heatsink.
All this will go away .. hmm~

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#3 2021-11-04 13:50:51

vanfanel
Member
Registered: 2021-10-27
Posts: 3  

Re: Video turns off on high CPU usage with Devuan 4.0 on Raspberry PI 4

@ShorTie: Yes, but throttling shouldn't cause video to go off. That's a different issue.

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#4 2023-03-17 23:22:06

cayenne
Member
Registered: 2020-06-26
Posts: 4  

Re: Video turns off on high CPU usage with Devuan 4.0 on Raspberry PI 4

I had a similar issue, except the Raspberry Pi completely froze on me. I didn't verify if it's caused by throttling, but I did confirm that turning off the second monitor by commenting out max_framebuffers=2 prevented the Pi from freezing when CPU's were maxed out. Furthermore, downgrading the kernel to 5.4.42 fixed the issue completely - I haven't had time to identify which kernel version the issue was introduced in.

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#5 2023-03-18 20:32:36

Altoid
Member
Registered: 2017-05-07
Posts: 1,475  

Re: Video turns off on high CPU usage with Devuan 4.0 on Raspberry PI 4

Hello:

vanfanel wrote:

... throttling shouldn't cause video to go off. That's a different issue.

Yes, you are quite right.

But throttling is a feature to protect the CPU from overheating and (eventually) blowing.

So (IMO) throttling must be avoided and that's what a heatsink is for.

In my 3B+ (now unused, a huge dissapointment) the adding of a heatsink to the chip without the speader made an important difference, at least in the comprehensive tests I ran at the time.

Edit: this video may be of use to you, if not there are others.

As always, YMMV.

Best,

A.

Last edited by Altoid (2023-03-19 13:53:29)

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