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Re: Bad desktop performance with Linux 5.8

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On 11/15/20 12:05 AM, Kévin Le Gouguec wrote:
> Hello,
> 
> I am running Debian Buster (XFCE) on a Dell Laptop[1] with some packages
> upgraded from backports[2], notably linux-image-amd64.  After upgrading
> to version 5.8, I started noticing some UI "choppiness".  To give a few
> examples:
> 
> - when typing (in any application, e.g. Emacs, Terminator, Firefox): at
>   its worst, I can type a bunch of words, sit back, wait a few seconds,
>   then watch the words appear letter by letter.
> 
> - when launching programs: startup times are very inconsistent; e.g. if
>   I loop on
>     while time emacs -Q --eval '(kill-emacs)' ; do continue ; done
>   or
>     while time terminator -x "bash -c exit" ; do continue ; done
>   times vary between 1× and 3× what I observe on kernel 5.7 (where times
>   barely vary at all, ±5% at most).
> 
> - when scrolling a PDF with Evince with the touchpad: the display
>   "freezes" (the pages do not seem to be scrolling) and jumps to the new
>   position after a few seconds; nonetheless, the pages *do* scroll
>   continuously, as the mouse pointer changes from an arrow to an I-beam,
>   presumably as text and whitespace move past it.
> 
> Neither htop, journalctl nor dmesg report anything suspicious to my
> untrained eye; the only difference I spotted was the CPU governor: on
> 5.7 it is "powersave"; on 5.8 it is "ondemand".  Naively cpufreq-setting
> all cores to powersave on 5.8 does not make the problem go away, though.
> 
> One curious thing is that looking at
>     watch -n0.5 grep MHz /proc/cpuinfo
> 
> - on 5.7, the system is very responsive, and the idle frequency is
>   around 800 MHz;
> - on 5.8, the system lags despite the idle frequency never going below
>   1700 MHz.
> 
> This might all be a red herring though, for all I know.  I did not
> immediately realize that the performance drops came from 5.8; I only
> understood that after studying a bunch of other hypotheses (uninstalling
> xserver-xorg-video-intel, disabling services such as speech-dispatcher
> and tor), coming up short, rebooting, opening Grub's "advanced options"
> and realizing that 5.7 was still on my system.
> 
> I've since rebooted multiple times on 5.7 and 5.8, and I'm positive that
> the problem only occurs with 5.8.
> 
> 
> I'm not sure what to look at next.  I've searched the Web for people
> having performance issues with 5.8, but nothing caught my eye.
> 
> I realize that "performance bad ☹" testimonies like this are probably
> not very actionable; let me know if there's anything I can do to make
> this "diagnosis" more precise.  Also, I hope this is the right place for
> this kind of support request; I assume it is too vague as-is for a
> proper bug report…  Let me know if I should post this elsewhere.
> 
> 
> Thank you for your time, and sorry for the poor report.
> 
> 
> [1] Dell Latitude 3190.  Attached outputs from lscpu and lspci:
> 
> 
> 
> [2] Potentially relevant backport packages:
> 
>         $ aptitude search '?narrow(?installed, ?archive(buster-backports)) ?name(firmware~|linux~|wireless)' -F '%p'
>         firmware-amd-graphics
>         firmware-iwlwifi
>         firmware-linux
>         firmware-linux-nonfree
>         firmware-misc-nonfree
>         linux-image-5.8.0-0.bpo.2-amd64
>         linux-image-amd64
>         wireless-regdb
> 
>     Potentially relevant non-free packages:
> 
>         $ aptitude search '?installed ?section(non-free/) !?name(-doc$~|^manpages-)' -F '%p'
>         amd64-microcode
>         firmware-amd-graphics
>         firmware-iwlwifi
>         firmware-linux
>         firmware-linux-nonfree
>         firmware-misc-nonfree
>         intel-microcode
> 


Hi Kévin,

Linux kernel version (5.8) is old and unsupported (EOL) branch. Maybe
you should wait for 5.9 to be available from backports or even 5.10 -
this version will be LTS and next Debian stable version will probably
use it. While waiting you can try to use 5.7 if possible.

Kind regards
Georgi

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Thread

Bad desktop performance with Linux 5.8 Kévin Le Gouguec <kevin.legouguec@gmail.com> - 2020-11-14 23:30 +0100
  Re: Bad desktop performance with Linux 5.8 Georgi Naplatanov <gosho@oles.biz> - 2020-11-15 00:50 +0100
    Re: Bad desktop performance with Linux 5.8 Kévin Le Gouguec <kevin.legouguec@gmail.com> - 2020-11-15 15:30 +0100
    Re: Bad desktop performance with Linux 5.8 Kévin Le Gouguec <kevin.legouguec@gmail.com> - 2020-12-06 16:10 +0100

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