Bug#1038981: capping maximum frequency no longer works in kernel 6.1
Package: linux-image-6.1.0-9-amd64
Version: 6.1.27-1
Below, I try to cap the frequency for each of my processor cores, but some cores resists:
# for i in `seq 0 7`; do echo "400000"> /sys/devices/system/cpu/cpu$i/cpufreq/scaling_max_freq && cat /sys/devices/system/cpu/cpu$i/cpufreq/scaling_cur_freq; done
400002
400004
399989
2300000
2300000
2300000
400013
399519
Moreover, the cores that resist changes each time; e.g., the next run yields this:
# for i in `seq 0 7`; do echo "400000"> /sys/devices/system/cpu/cpu$i/cpufreq/scaling_max_freq && cat /sys/devices/system/cpu/cpu$i/cpufreq/scaling_cur_freq; done
400024
2300000
400002
400020
2300000
400000
399930
400008
I tried to read the frequency via /proc/cpuinfo:
# for i in `seq 0 7`; do echo "400000"> /sys/devices/system/cpu/cpu$i/cpufreq/scaling_max_freq; done && cat /proc/cpuinfo | grep MHz
cpu MHz : 400.001
cpu MHz : 399.989
cpu MHz : 2300.000
cpu MHz : 400.107
cpu MHz : 1028.210
cpu MHz : 399.942
cpu MHz : 400.001
cpu MHz : 400.004
I also tried to use tlp (yes, I said TLP_DEFAULT_MODE=BAT, TLP_PERSISTENT_DEFAULT=1, CPU_BOOST_ON_BAT=0, and CPU_HWP_DYN_BOOST_ON_BAT=0) and sysfs packages; all methods yield the similar results: capping the frequency of all cores doesn't work. I tried to cap all at, say, 800 MHz, 1.2 GHz, and 2 GHz instead, but the result is often (but not always!) the same: a few cores often (but not always!) resist and run at higher frequencies up to 2.4 GHz. Only seldom I see the expected:
# for i in `seq 0 7`; do echo "400000"> /sys/devices/system/cpu/cpu$i/cpufreq/scaling_max_freq; done && cat /proc/cpuinfo | grep MHz
cpu MHz : 400.004
cpu MHz : 399.988
cpu MHz : 399.999
cpu MHz : 400.011
cpu MHz : 399.980
cpu MHz : 400.048
cpu MHz : 400.002
cpu MHz : 400.008
But running cat /proc/cpuinfo | grep MHz a few seconds later yields again a few lines with 2300.000.
The governor is powersave everywhere.
For kernel 5 with Debian 11 (which I can no longer test), everything worked like a charm (or at least I always observed all-400-MHz back then). So either the new kernel is erroneous or my processor broke somehow (perhaps, during the upgrade). It has Intel(R) Core(TM) i7-10610U CPU @ 1.80GHz.
Who is the culprit? What to do?
Gratefully,
AlMa
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