X11 forwarding extremely slow (unusable) after Cygwin upgrade (starting from cygwin1.dll version 3.1.0-0.4)

Takashi Yano takashi.yano@nifty.ne.jp
Sat Jan 4 01:51:00 GMT 2020

On Thu, 2 Jan 2020 22:16:02 +0000
Ken Brown wrote:
> I think this narrows it down to one of the following commits:

I looked into this probelm and found the issue occurs after
the following commit.

> commit 915fcd0ae8d83546ce135131cd25bf6795d97966
> Author: Takashi Yano <takashi.yano@nifty.ne.jp>
> Date:   Thu Sep 5 13:22:54 2019 +0900
>      Cygwin: pty: Fix select() with pseudo console support.

I investigated this deeper, and found:

1) xterm in ssh -Y session calls select() about 1000 times
   at startup.
2) pi->thread->detach() in pty_slave_cleanup() takes about
   20usec in usual, however, it takes more than 10msec
   in ssh -Y session.

As a result, start up of xterm takes more than 10 sec.

I have no idea so far why cygthread::detach() becomes
so slow in ssh -Y session. :-(

Takashi Yano <takashi.yano@nifty.ne.jp>

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