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

[Thorsten Leemhuis <regressions@leemhuis.info>]

TWIMC: this mail is primarily send for documentation purposes and for
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Culprit got reverted:
https://git.kernel.org/torvalds/c/075b7d363c675ef7fa03918881caeca3458e2a96

#regzbot fixed-by: 075b7d363c675ef7fa03918881caeca3458e2a96

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

P.S.: As the Linux kernel's regression tracker I'm getting a lot of
reports on my table. I can only look briefly into most of them and lack
knowledge about most of the areas they concern. I thus unfortunately
will sometimes 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
in a public reply, it's in everyone's interest to set the public record
straight.

On 26.01.22 12:23, Thorsten Leemhuis wrote:
> 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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