Bug 1325509

Description of problem:
The Conflicts=plymouth-quit.service setting in the [Unit] section of /usr/lib/systemd/system/gdm.service causes the startup process to slow down significantly (as timed manually and also as reported by systemd-analyze) and the GDM login screen to take a long time to appear. Disabling this Conflicts parameter shows a significant reduction in startup time, comparable to those of Fedora Spins which do not use GDM. Alternatively, using a different display manager (such as LightDM) also increases startup speed. On my system, there is a difference of about 10 seconds.

Version-Release number of selected component (if applicable):
gdm-1:3.18.2-2.fc23.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Install a Fedora 23 Spin (such as Fedora Xfce or Fedora KDE), or install a display manager other than GDM (such as LightDM) on Fedora 23 Workstation and enable it (systemctl enable --force lightdm.service) so that it is used on the next boot.
2. After logging in, run systemd-analyze and note the total startup time. Also run systemd-analyze critical-chain and note the startup points of multi-user.target and graphical.target (i.e., at what time during the boot process they were started).
3. On the same machine, install Fedora 23 Workstation, or install GDM and enable it on a Fedora Spin (systemctl enable --force gdm.service), so that GDM is used as the display manager on the next boot. For a new installation, (re-)booting a couple of times may be necessary to rule out (apparently) fast initial startups.
4. Wait for the GDM login screen to appear, then after logging in, run systemd-analyze and systemd-analyze critical-chain.

Actual results:
Total startup time is significantly more than comparable startups not using GDM. Verify that multi-user.target and graphical.target start up much later than the other services, and also as compared to a startup not using GDM. Compare the readings to those taken in step 2 above.

NB: Total startup time may be a few seconds more on Fedora 23 Workstation than on a Fedora Spin because of the time taken by libvirtd.service which is enabled by default on Workstation.

Expected results:
Total startup time should be similar to a startup not using GDM. All other distributions on which I have tried GDM have low startup times satisfying this condition.

Additional info:
Disable the Conflicts=plymouth-quit.service line in /usr/lib/systemd/system/gdm.service, reboot and repeat step 4 from above. Verify that the total startup time and the times at which multi-user.target and graphical.target are started have come down and become similar to those for non-GDM startups.
NB: Using a gdm.service file from /etc/systemd/system/ may cause the Plymouth splash to not appear during the shutdown process.

Disabling the Conflicts parameter causes a disruption in the transition from the Plymouth splash screen to the (GDM) login screen instead of allowing the direct transition seen when it is in place. This behaviour (with the disruption) is the same as that on Fedora Spins and also on other distributions which use GDM.

The converse of this situation is true to some extent. Adding a Conflicts=plymouth-quit.service line to another display manager's service unit configuration which is then used may cause some delay in startup (I have seen an increase of about 3 seconds in total startup time in the case of LightDM).