Dell Latitude thermal throttling

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On some Dell Latitude laptops, you may encounter random shutdowns on heavy load. We believe this is because the SMSC EC is overly conservative by default; it is in charge of handling thermals and fan control on this machine. Our theory is that coreboot needs to write certain EC commands to allow higher temperatures; please read:

https://codeberg.org/libreboot/lbmk/issues/202

Basically, what you need to do is:

Also: the intel_pstate driver can be used to artifically cap CPU speed. See:

https://www.kernel.org/doc/html/v4.12/admin-guide/pm/intel_pstate.html

When you use this machine, it is recommended that you cap the CPU speed once you’ve booted into Linux. Set it to something like 50% at first. Then run a stress test, for example:

stress -c x

Where x is the number of CPU cores, e.g. 2. Monitor the temperatures using something like xsensors, making sure the CPU doesn’t exceed 80c temperature.

You can also monitor CPU speeds in Linux like so:

watch -n .2 grep MHz /proc/cpuinfo

This will let you know what speed you’re at. You can use this to determine whether the intel_pstate driver is working. How to cap speed to 50 percent, as in the above example:

echo 50 > /sys/devices/system/cpu/cpufreq/intel_pstate/max_perf_pct

Gradually increase the CPU speed (up to 100 on max_perf_pct), waiting a few minutes each time. You should ensure that your machine does not exceed 80C.

Dell’s thermal safety is far too protective by default, on some of these, and we don’t yet know how to properly configure it. Running a CPU below 80c in temperature and never higher than that, is a good idea anyway, for the long term life of your CPU.

Regardless, thermal shutdown is extremely reliable on this machine, but Dell makes it shut down earlier, before it can even start to CPU throttle.

Markdown file for this page: https://libreboot.org/docs/hardware/dell_thermal.md

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