[SOLVED] 5 second delay when when opening X11 window from SSH session

andris · 2023-10-11 14:06:12

Noticed about 5 second delay when opening X11 window from remote SSH session to any host I tried (X11 forwarding enabled from command line) after upgrade to OpenSSH 9.5p1.
For example if the remote application is Emacs, then also opening another window (M-X 3 2) experiences the same delay. I experienced this on 2 ArchLinux systems after this upgrade.

Downgrade back to OpenSSH 9.4p1 fixes the delay. After downgrade windows open from SSH session much faster.

Desktop environment: KDE
Remote systems I have tried: RHEL8, RHEL9 and additionally RockyLinux 8 and 9 LXC kontainers in the same system
Local 1GB network

What could be the reason of such annoying delay and how to avoid it?

Andris

Last edited by andris (2023-10-12 17:24:31)

seth · 2023-10-11 14:55:52

For example if the remote application is Emacs, then also opening another window (M-X 3 2)

Is this also the case when not using a shortcut but eg. just running xterm?

andris · 2023-10-11 17:17:21

I'm not using shortcut: just starting required application. Some examples:

gitk &
git gui &
emacs &

In all these cases initial window opening is delayed. Also all these can open new windows and also these are delayed

Last edited by andris (2023-10-11 17:19:14)

seth · 2023-10-11 19:18:54

I thought because of the "M-X 3 2" - there're also a couple of commits in openssh dealing w/ input delay randomization and I figured it might throw off the XEvent timestamps.
Is only window creation affected? Does eg "xrandr -q" respond immediately?

andris · 2023-10-12 10:52:01

I see the same about delay also when opening the first application window (for example xterm, or any of commands, I mentioned yesterday) and next ones

Also:
xrandr -q has some response delay both with openssh-9.4p1 and openssh-9.5p1 (I downgraded only one of 2 systems, where I run X11 applications in SSH sessions regularly). For latest tests SSH session was from ArchLinux to RHEL9 system (openssh-8.7p1-30.el9_2.x86_64)

seth · 2023-10-12 13:29:02

No, what I meant is whether Xlib calls are slow besides XCreateWindow (eg. using xrandr) - is "some delay" also 5s or way less (like ½s to actually poll the outputs etc) - what about eg. "xdpyinfo" as alternative?

andris · 2023-10-12 17:21:55

It seems that new OpenSSH-9.5p1 feature partially breaks X11 forwarding and causes this delay.

Disabling it ObscureKeystrokeTiming=no on ArchLinux side fixes the delay.

Command 'time xterm -e true' (can measure delay easy enough)

=== openssh-9.4p1 installed

real    0m0,100s
user    0m0,014s
sys     0m0,010s

=== openssh-9.5p1 installed (3 attempts)

real    0m4,828s
user    0m0,021s
sys     0m0,011s

real    0m4,866s
user    0m0,016s
sys     0m0,015s

real    0m5,093s
user    0m0,016s
sys     0m0,016s

New connection opened with: 'ssh -A -Y -o ObscureKeystrokeTiming=no 192.168.1.11' (and openssh-9.5p1 installed)

real    0m0,160s
user    0m0,016s
sys     0m0,013s

Arch Linux

#1 2023-10-11 14:06:12

[SOLVED] 5 second delay when when opening X11 window from SSH session

#2 2023-10-11 14:55:52

Re: [SOLVED] 5 second delay when when opening X11 window from SSH session

#3 2023-10-11 17:17:21

Re: [SOLVED] 5 second delay when when opening X11 window from SSH session

#4 2023-10-11 19:18:54

Re: [SOLVED] 5 second delay when when opening X11 window from SSH session

#5 2023-10-12 10:52:01

Re: [SOLVED] 5 second delay when when opening X11 window from SSH session

#6 2023-10-12 13:29:02

Re: [SOLVED] 5 second delay when when opening X11 window from SSH session

#7 2023-10-12 17:21:55

Re: [SOLVED] 5 second delay when when opening X11 window from SSH session

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