openssh bugs - Jan 2024 - [Bug 3655] New: Default ObscureKeystrokeTiming makes X forwarding really slow

https://bugzilla.mindrot.org/show_bug.cgi?id=3655

            Bug ID: 3655
           Summary: Default ObscureKeystrokeTiming makes X forwarding
                    really slow
           Product: Portable OpenSSH
           Version: 9.6p1
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: ole.laursen at gmail.com

This is easy to reproduce with something like xterm or emacs:

$ ssh -X localhost
$ xterm
$ emacs

They are both slow to display their windows, and interaction is laggy.
In Emacs, text selection has several seconds of lag.

Meanwhile

ssh -X -oObscureKeystrokeTiming=no localhost

works fine.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3655

Andreas Gustafsson <gson at araneus.fi> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gson at araneus.fi

--- Comment #1 from Andreas Gustafsson <gson at araneus.fi> ---
I am also affected by this bug.  An X11 application suddenly became
slow to the point of unusability, and it took quite a lot of detective
work to determine that the cause was neither the application itself nor
the X server but ssh.

To help quantify the worst-case slowdown, I am attaching a test program
that makes 1000 round-trip requests to the X server.  Running it via
the ssh included in macOS Sonoma 14.4.1 (OpenSSH_9.6p1) shows:

$ ssh -X -oObscureKeystrokeTiming=no localhost
$ time ./test
real    0m0.120s
user    0m0.007s
sys     0m0.018s
$ exit

$ ssh -X localhost
$ time ./test
real    0m24.095s
user    0m0.018s
sys     0m0.066s

That's a slowdown by a factor of 200.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3655

--- Comment #2 from Andreas Gustafsson <gson at araneus.fi> ---
Created attachment 3800
  --> https://bugzilla.mindrot.org/attachment.cgi?id=3800&action=edit
Test program that performs 1000 round-trip X11 requests

-- 
You are receiving this mail because:
You are watching the assignee of the bug.