Re: [Bug 215533] [BISECTED][REGRESSION] UI becomes unresponsive every couple of seconds

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Jan, author of 0e8ae5a6ff59, linux-pci]

On Wed, Jan 26, 2022 at 08:18:12AM +0000, bugzilla-daemon@bugzilla.kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=215533
> 
> --- Comment #1 from joey.corleone@mail.ru ---
> 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
> 
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