control: summary -1 0 slow to start user ssh session (11 seconds)
Hi,
I reopened this bug since the current unstable package isn't good enough
and requires some touch up to get accepted for testing.
Problem:
========
* The default desktop Debain install is Gnome-wayland.
* Some localization tasks pull in im-config (its important)
* The testing had im-config=0.39-1
* Im-config=0.39-1 caused major degradation to the ssh login with
11 unresponsive latency under wayland+systemd.
* The root cause was the slow script run by im-config during the start of
a new process to set its environment variable using the systemd's
systemd.environment-generator(7).
* this performance degradation of the default system is unacceptable.
Bug #925160 back ground:
========================
Many unnoticed performance bugs crept into im-config to cause this bug.
* Nov 2011 (version 0.5) -- older than oldstable/jessie
Since im-config is ARCH=all package, it used "*" as the path part for
the multiarch such as x86_64-linux-gnu
--> This should have been "*-*-*" instead of just "*"
* Feb 2015 (version 0.27-2) jessie released version
* Dec 2016 (version 0.30-1) stretch released version
* Bug #905129: im-config: Wrongly run shell scripts with user's shell
interpreter, raises error with zsh (Jul 2018)
This was really a problem of KDE + sddm.
* Aug 2018 (0.37-1) -- during buster development cycle
im-config worked around bug #905129 by replacing shell glob with a
shell function call which runs script with "find" command.
--> This should have been worked around by using the simple one liner:
if [ x != x"$ZSH_NAME" ]; then emulate -R sh ; fi
* Mar 2019 (version 0.40-1)
Patch provided by Y. Yoshino was applied to make im-config useful for
Gnome-wayland. Since gnome-session has no easy hook script
mechanism like /etc/X11/Xsession.d/* files for X, this patch decided
to use systemd.environment-generator(7) to set the user environment.
--> This script run the problematic slow code twice which made situation
worse.
--> This startup code should have been disabled if it finds
ibus-daemon just as gnome-session (main.c) does.
--> This startup code should run only when it finds
XDG_SESSION_TYPE=wayland (ideally -- but can't check it if
systemd.environment-generator is used)
* Bug #925160 systemd: user session slow to start (11 seconds) (Mar 2019)
Since 0.40-1 used systemd.environment-generator, the hook scrip was
run even for ssh login and delay of 11 seconds was noticed. ssh with
X-session doesn't have this problem for ssh and 11 second during X
start up may not be as annoying.
How to solve Bug #925160:
=========================
* Fix glob to use "*-*-*"
* Use "emulate -R sh" trick (not script with "find") for zsh
* save environment variables to avoid running the problematic slow code
twice
* check existence of ibus-daemon and disable systemd.environment-generator
script if you find it.
Technical reference:
====================
$ cd /usr/lib
$ ( ls -1d * ; ls -1d * )|wc -l
734
$ ls -1d *-* |wc -l
74
$ ls -1d *-*-* |wc -l
18
So not running slow glob twice and changing "*" --> "*-*-*" can improve
speed 40 times!
Shell glob approach is faster than script with "find"
Future vision:
==============
I see 2 parts of code which may be patched to make cleaner solution
* gnome-session ibus related environment variable setting
* gnome-shell: ibus starting code
But that is for future.
im-config's complicated time consuming code may be useless to start with
from today's situation since settings such as:
GTK_IM_MODULE=xim
QT4_IM_MODULE=xim
are not good idea . It is usually a source of lost key input etc.
It's now better to use settings such as:
GTK_IM_MODULE=ibus
QT4_IM_MODULE=ibus
This simplify code greatly but doing this may be too late for buster
under freeze.
Osamu
