pci: UI becomes unresponsive every couple of seconds (fwd from bugzilla)

[Thorsten Leemhuis <regressions@leemhuis.info>]

Hi, this is your Linux kernel regression tracker speaking.

There is a regression in bugzilla.kernel.org I'd like to add to the
tracking:

#regzbot introduced: 0e8ae5a6ff5952253cd7cc0260df838ab4c21009
#regzbot from: joey.corleone@mail.ru
#regzbot title: pci: UI becomes unresponsive every couple of seconds
#regzbot link: https://bugzilla.kernel.org/show_bug.cgi?id=215533

Quote:

> I accidentally sent the report prematurely. So here come my findings:
> 
> Since 5.16
> (1) my system becomes unresponsive every couple of seconds (micro lags), which makes it more or less unusable.
> (2) wrong(?) CPU frequencies are reported. 
> 
> - 5.15 works fine.
> - Starting from some commit in 5.17, it seems (1) is fixed (unsure), but definitely not (2).
> 
> I have bisected the kernel between 5.15 and 5.16, and found that the offending commit is 0e8ae5a6ff5952253cd7cc0260df838ab4c21009 ("PCI/portdrv: Do not setup up IRQs if there are no users"). Bisection log attached.
> 
> Reverting this commit on linux-git[1] fixes both (1) and (2).
> 
> Important notes:
> - This regression was reported on a DELL XPS 9550 laptop by two users [2], so it might be related strictly to that model. 
> - According to user mallocman, the issue can also be fixed by reverting the BIOS version of the laptop to v1.12.
> - The issue ONLY occurs when AC is plugged in (and stays there even when I unplug it).
> - When booting on battery power, there is no issue at all.
> 
> You can easily observe the regression via: 
> 
> watch cat /sys/devices/system/cpu/cpu[0-9]*/cpufreq/scaling_cur_fre
> 
> As soon as I plug in AC, all frequencies go up to values around 3248338 and stay there even if I unplug AC. This does not happen at all when booted on battery power. 
> 
> Also note: 
> - the laptop's fans are not really affected by the high frequencies.
> - setting the governor to "powersave" has no effect on the frequencies (as compared to when on battery power).
> - lowering the maximum frequency manually works, but does not fix (1).
> 
> [1] https://aur.archlinux.org/pkgbase/linux-git/ (pulled commits up to 0280e3c58f92b2fe0e8fbbdf8d386449168de4a8).
> [2] https://bbs.archlinux.org/viewtopic.php?id=273330

Ciao, Thorsten (wearing his 'Linux kernel regression tracker' hat)

P.S.: As a Linux kernel regression tracker I'm getting a lot of reports
on my table. I can only look briefly into most of them. Unfortunately
therefore I sometimes will get things wrong or miss something important.
I hope that's not the case here; if you think it is, don't hesitate to
tell me about it in a public reply, that's in everyone's interest.

BTW, I have no personal interest in this issue, which is tracked using
regzbot, my Linux kernel regression tracking bot
(https://linux-regtracking.leemhuis.info/regzbot/). I'm only posting
this mail to get things rolling again and hence don't need to be CC on
all further activities wrt to this regression.

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