Public bug reported:

I've noticed on Lenovo X220 and X230 laptops that pressing brightness
keys on Yakkety seems less responsive and slower than Xenial.  I ran
forkstat on Xenial and just observed udev being forked off:

Xenial:
$ sudo forkstat
Time     Event  PID  Info  Duration Process
17:37:35 fork    273 parent          /lib/systemd/systemd-udevd
17:37:35 fork   1977 child           /lib/systemd/systemd-udevd
17:37:35 exit   1977      0    0.008 /lib/systemd/systemd-udevd

Whereas on Yakkety, there is far more activity:
Time     Event  PID  Info  Duration Process
16:35:34 fork   2626 parent          update-notifier
16:35:34 fork   2645 child           update-notifier
16:35:34 exec   2645                 /usr/bin/python3 
/usr/share/apport/apport-checkreports
16:35:34 exit   2645    256    0.221 /usr/bin/python3 
/usr/share/apport/apport-checkreports
16:35:34 fork   2626 parent          update-notifier
16:35:34 fork   2646 child           update-notifier
16:35:34 exec   2646                 /usr/bin/python3 
/usr/share/apport/apport-checkreports --system
16:35:34 exit   2646    256    0.188 /usr/bin/python3 
/usr/share/apport/apport-checkreports --system
16:35:36 fork   1576 parent          
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 fork   2647 child           
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 exec   2647                 
/usr/lib/unity-settings-daemon/usd-backlight-helper --get-max-brightness
16:35:36 exit   2647      0    0.008 
/usr/lib/unity-settings-daemon/usd-backlight-helper --get-max-brightness
16:35:36 fork   1576 parent          
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 fork   2648 child           
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 exec   2648                 
/usr/lib/unity-settings-daemon/usd-backlight-helper --get-brightness
16:35:36 exit   2648      0    0.006 
/usr/lib/unity-settings-daemon/usd-backlight-helper --get-brightness
16:35:36 fork   1576 parent          
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 fork   2649 child           
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 exec   2649                 
/usr/lib/unity-settings-daemon/usd-backlight-helper --get-brightness
16:35:36 exit   2649      0    0.007 
/usr/lib/unity-settings-daemon/usd-backlight-helper --get-brightness
16:35:36 fork   1576 parent          
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 fork   2650 child           
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 exec   2650                 
/usr/lib/unity-settings-daemon/usd-backlight-helper --get-max-brightness
16:35:36 exit   2650      0    0.006 
/usr/lib/unity-settings-daemon/usd-backlight-helper --get-max-brightness
16:35:36 fork   1576 parent          
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 fork   2651 child           
/usr/lib/unity-settings-daemon/unity-settings-daemon
16:35:36 exec   2651                 pkexec 
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 2250
16:35:36 clone  2651 parent          pkexec 
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 2250
16:35:36 clone  2652 thread          pkexec 
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 2250
16:35:36 clone  2651 parent          pkexec 
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 2250
16:35:36 clone  2653 thread          pkexec 
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 2250
16:35:36 fork      1 parent          /sbin/init splash
16:35:36 fork   2654 child           /sbin/init splash
Time     Event  PID  Info  Duration Process
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2655 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2656 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2657 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2658 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2659 child           /lib/systemd/systemd-udevd
16:35:36 exit   2659      0    0.005 /lib/systemd/systemd-udevd
16:35:36 exit   2658      0    0.006 /lib/systemd/systemd-udevd
16:35:36 exit   2657      0    0.007 /lib/systemd/systemd-udevd
16:35:36 exit   2656      0    0.008 /lib/systemd/systemd-udevd
16:35:36 exit   2655      0    0.008 /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2660 child           /lib/systemd/systemd-udevd
16:35:36 exit   2660      0    0.001 /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2661 child           /lib/systemd/systemd-udevd
16:35:36 exit   2661      0    0.002 /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2662 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2663 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2664 child           /lib/systemd/systemd-udevd
16:35:36 fork   2654 parent          /sbin/init splash
16:35:36 fork   2665 child           (systemd)
16:35:36 exec   2654                 /lib/systemd/systemd --user
16:35:36 exit   2662      0    0.010 /lib/systemd/systemd-udevd
16:35:36 exit   2664      0    0.007 /lib/systemd/systemd-udevd
Time     Event  PID  Info  Duration Process
16:35:36 exit   2663      0    0.009 /lib/systemd/systemd-udevd
16:35:36 fork   2654 parent          /lib/systemd/systemd --user
16:35:36 fork   2666 child           /lib/systemd/systemd --user
16:35:36 exit   2666      0    0.001 /lib/systemd/systemd --user
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2667 child           /lib/systemd/systemd-udevd
16:35:36 exit   2667      0    0.003 /lib/systemd/systemd-udevd
16:35:36 fork   2654 parent          /lib/systemd/systemd --user
16:35:36 fork   2668 child           /lib/systemd/systemd --user
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2669 child           /lib/systemd/systemd-udevd
16:35:36 exit   2669      0    0.002 /lib/systemd/systemd-udevd
16:35:36 exec   2668                 /bin/systemctl --user set-environment 
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/0/bus
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2670 child           /lib/systemd/systemd-udevd
16:35:36 exit   2670      0    0.001 /lib/systemd/systemd-udevd
16:35:36 exit   2668      0    0.009 /bin/systemctl --user set-environment 
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/0/bus
16:35:36 fork      2 parent          [kthreadd]
16:35:36 fork   2671 child           [kworker/u16:4]
16:35:36 exec   2671                 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/user@0.service/dbus.socket]
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2672 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2673 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2674 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2675 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2676 child           /lib/systemd/systemd-udevd
16:35:36 exit   2671      0    0.005 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/user@0.service/dbus.socket]
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
Time     Event  PID  Info  Duration Process
16:35:36 fork   2677 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2678 child           /lib/systemd/systemd-udevd
16:35:36 exit   2653      0    0.126 pkexec 
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 2250
16:35:36 exit   2652      0    0.126 pkexec 
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 2250
16:35:36 exec   2651                 
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 2250
16:35:36 exit   2673      0    0.013 /lib/systemd/systemd-udevd
16:35:36 exit   2672      0    0.013 /lib/systemd/systemd-udevd
16:35:36 exit   2678      0    0.011 /lib/systemd/systemd-udevd
16:35:36 exit   2675      0    0.013 /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2679 child           /lib/systemd/systemd-udevd
16:35:36 exit   2674      0    0.020 /lib/systemd/systemd-udevd
16:35:36 exit   2651      0    0.146 
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 2250
16:35:36 fork      2 parent          [kthreadd]
16:35:36 fork   2680 child           [kworker/u16:5]
16:35:36 exec   2680                 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/session-2.scope]
16:35:36 exit   2676      0    0.022 /lib/systemd/systemd-udevd
16:35:36 exit   2679      0    0.003 /lib/systemd/systemd-udevd
16:35:36 exit   2677      0    0.022 /lib/systemd/systemd-udevd
16:35:36 exit   2680      0    0.003 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/session-2.scope]
16:35:36 fork   2654 parent          /lib/systemd/systemd --user
16:35:36 fork   2681 child           /lib/systemd/systemd --user
16:35:36 exec   2681                 /bin/kill -s 58 2654
16:35:36 exit   2681      0    0.200 /bin/kill -s 58 2654
16:35:36 fork      2 parent          [kthreadd]
16:35:36 fork   2682 child           [kworker/u16:5]
16:35:36 exec   2682                 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/user@0.service/systemd-exit.service]
16:35:36 exit   2654      0    0.294 /lib/systemd/systemd --user
16:35:36 exit   2682      0    0.004 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/user@0.service/systemd-exit.service]
16:35:36 exit   2665      9    0.272 (systemd)
16:35:36 fork      2 parent          [kthreadd]
Time     Event  PID  Info  Duration Process
16:35:36 fork   2683 child           [kworker/u16:5]
16:35:36 exec   2683                 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/user@0.service/init.scope]
16:35:36 fork      2 parent          [kthreadd]
16:35:36 fork   2684 child           [kworker/u16:4]
16:35:36 fork      2 parent          [kthreadd]
16:35:36 fork   2685 child           [systemd-cgroups]
16:35:36 exec   2684                 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/user@0.service]
16:35:36 exec   2685                 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice]
16:35:36 exit   2683      0    0.005 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/user@0.service/init.scope]
16:35:36 exit   2685      0    0.005 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice]
16:35:36 exit   2684      0    0.007 [/lib/systemd/systemd-cgroups-agent 
/user.slice/user-0.slice/user@0.service]
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2686 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2687 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2688 child           /lib/systemd/systemd-udevd
16:35:36 fork    233 parent          /lib/systemd/systemd-udevd
16:35:36 fork   2689 child           /lib/systemd/systemd-udevd
16:35:36 exit   2687      0    0.014 /lib/systemd/systemd-udevd
16:35:36 exit   2689      0    0.013 /lib/systemd/systemd-udevd
16:35:36 exit   2686      0    0.015 /lib/systemd/systemd-udevd
16:35:36 exit   2688      0    0.015 /lib/systemd/systemd-udevd

I suspect some of this overhead explains the slower responsive feel to
the brightness buttons. Anyhow, seems like a bit of an overkill for all
these processes to be running especially compared to Xenial.

** Affects: linux (Ubuntu)
     Importance: High
         Status: New


** Tags: kernel-4.8

** Changed in: linux (Ubuntu)
   Importance: Undecided => High

** Summary changed:

- brightness keys are handles slower in Yakkety than Xenial
+ brightness keys are handled slower in Yakkety than Xenial

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https://bugs.launchpad.net/bugs/1626651

Title:
  brightness keys are handled slower in Yakkety than Xenial

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