bug#73046: 29.4; Emacs 100% CPU usage for several seconds when opening dired buffer over TRAMP

[Eli Zaretskii <eliz@gnu.org>]

> From: Suhail Singh <suhailsingh247@gmail.com>
> Cc: suhailsingh247@gmail.com,  Michael Albinus <michael.albinus@gmx.de>,
>   73046@debbugs.gnu.org
> Date: Fri, 06 Sep 2024 13:47:54 -0400
> 
> > How long does it take to fetch a file of, say 20 KBytes?
> 
> Given a 20kb file generated via:
> #+begin_src sh :results verbatim
>   mkdir -p /tmp/test
>   cd /tmp/test
>   dd if=/dev/urandom of=upload_test bs=10k count=2
>   du -sh /tmp/test/upload_test
> #+end_src
> 
> #+RESULTS:
> : 20K	/tmp/test/upload_test
> 
> It takes ~4-6s to upload:
> #+begin_src sh :results verbatim
>   cd /tmp/test
>   {
>       time scp upload_test scp://${affected-host}//tmp/upload_test
>   } 2>&1
> #+end_src
> 
> #+RESULTS:
> : 
> : real	0m4.255s
> : user	0m0.008s
> : sys	0m0.002s
> 
> And a similar time to download:
> #+begin_src sh :results verbatim
>   cd /tmp/test
>   {
>       time scp scp://${affected-host}//tmp/upload_test ./download_test
>   } 2>&1
> #+end_src
> 
> #+RESULTS:
> : 
> : real	0m5.638s
> : user	0m0.007s
> : sys	0m0.000s
> 
> 
> > Also, if font-lock is disabled, does the problem go away?
> 
> As noted in the original message:
> 
> >>> Disabling global-font-lock-mode, makes the situation better.
> 
> Things are still sluggish after disabling font-lock, but they are *much*
> better (i.e., instead of a ~10s delay for revert-buffer we are down to
> less than a second).  The remaining sluggishness seems reasonable given
> what I know about the connection speed, but I have not done extensive
> quantitative testing.  As such, while I cannot say with certainty if
> "the problem" goes away entirely, or only mostly, it does improve
> significantly.

So if it takes 4 to 5 sec to move a 20KB file, then how much stuff
needs to be moved for the Dired listing?  What does the below show, if
you run it on that remote machine?

  $ ls -al | wc

It needs to show around 40KB to explain 10 sec of delay.