[Possible bug]: thermal and an scaling governor issues

[Marcos Dione <mdione@grulic.org.ar>]

    Before anything, please CC: me, as I'm not subscribed to the list.

    Right now I'm running 6.12.38+deb13-amd64 from Debian
testing/unstable, which are the same due to the freeze until next week :)

    It all seems to have started at the beginning of the year. The
symptom was hiccups which could be seen as high load (f.i. 40 on an 8
core machine) with not much CPU usage. I tracked it down to
prometheus-node-exporter stalling on disk accesses. Looking with strace
I find there were multisecond reads on files related to sensonrs in
general, which I still experience:

23:30:13.855780 (+     0.004490) openat(AT_FDCWD, "/sys/class/hwmon/hwmon1/in0_input", O_RDONLY) = 3 <0.000152>
23:30:13.856286 (+     0.000494) fstat(3, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0 <0.000052>
23:30:13.856574 (+     0.000286) read(3, "12686\n", 4096) = 6 <3.196855>
23:30:17.053632 (+     3.197072) close(3) = 0 <0.000061>

23:33:39.689505 (+     0.000167) openat(AT_FDCWD, "/sys/class/hwmon/hwmon5/fan1_input", O_RDONLY) = 3 <0.000081>
23:33:39.689708 (+     0.000201) fstat(3, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0 <0.000047>
23:33:39.689870 (+     0.000164) read(3, "3225\n", 4096) = 5 <0.018190>
23:33:39.708237 (+     0.018376) close(3) = 0 <0.000060>

23:33:39.710771 (+     0.000151) openat(AT_FDCWD, "/sys/class/hwmon/hwmon5/fan2_input", O_RDONLY) = 3 <0.000073>
23:33:39.710947 (+     0.000176) fstat(3, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0 <0.000042>
23:33:39.711089 (+     0.000141) read(3, "3215\n", 4096) = 5 <0.128783>
23:33:39.840088 (+     0.129024) close(3) = 0 <0.000067>

    Accumulating all those reads led to the node exporter to gradually
take more and more time to finish the scrape, going beyond the 15s
between scrapes. I'm not sure, but I think at some point the node
exporter just launches goroutines to do these sweeps and they just pile
up one on top of the other. I had to disable the collectors.

    That's problem #1.

    Today I was (ab)using the 8 cores compiling stuff, while watching
videos, so a load of above 10. I'm using (KDE's?) upowerd, but I'm not
sure this has any impact. KDE's power plasmoid shows it's using the
p[erformance governor, but checking the files I get another story:

$ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
powersave
powersave
powersave
powersave
powersave
powersave
powersave
powersave

    So I manually set them to performance:

$ echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
performance

$ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
performance
performance
performance
performance
performance
performance
performance
performance

    But CPU frequency stays below the 1GHz for a 3.8GHz CPU and the
temps stay below 47C.

    Now, I'm not sure if these things are connected, but I wager they
do. Even if they aren't, they are annoying independently. The problem
is: I have no idea how to debug this. I see no particular info in dmesg.
I tried other Debian kernel versions all down to the latest 5.x I could
get. I'm open to a slow tracking down of this thing because it has been
working for some 6.5y before these behaviors. My other alternative is to
buy new HW.

    Cheers,

	-- Marcos.