bug#44007: 26.3; Strange shell mode performance

[Andreas Röhler]

On 15.10.20 16:34, Herman, Geza wrote:
> Sure!
>
> 1. execute emacs by "emacs -Q"
> 2. M-x shell RET
> 3. in the shell, execute "seq 100000" (or cat a large file)
> 4. immediately after you hit enter on "seq 100000" press enter again
>
> It doesn't reproduce 100% unfortunately. It seems that if it doesn't 
> reproduce, you need to start from step 1., so it has a higher chance 
> to happen.
>
> Another strange thing is that enter can have the opposite effect as 
> well: if I press it during "seq 100000" several times (not immediately 
> after "seq 100000", but after ~1 sec), it can make seq slower. Instead 
> of the usual 3-4 sec, it slows down to >10 sec.
> (I measured by "time seq 100000"). It seems that the more enter I 
> press, the slower it gets. But maybe it's a different issue.
>
> On 2020-10-15 16:10, Eli Zaretskii wrote:
> > > From: Herman@debbugs.gnu.org, Géza <geza.herman@gmail.com>
> > > Date: Thu, 15 Oct 2020 11:53:16 +0200
> > >
> > > I'm experiencing strange shell (comint) mode performance. If I cat a 10
> > > MB file, it takes 1:20 to cat it. Emacs uses only 30% cpu. But, if I
> > > press enter after I send the cat command, it speeds up, and it only
> > > takes 8 sec (emacs cpu usage goes up to 100%).
> > >
> > > Same thing: if I execute "seq 100000" in a small emacs window, it takes
> > > ~3 seconds. But, if I press enter after executing seq, it takes only 
> > > 0.4
> > > sec (this is not 100% reproducible, sometimes pressing enter doesn't
> > > make a difference).
> > > (I executed comint-clear-buffer before measurements)
> > Can you please describe a detailed reproduction recipe, starting from
> > "emacs -Q"?  It is not exactly clear from the above whether you do
> > this in a shell-mode buffer or in some other mode, where exactly do
> > you press Enter, etc.  A detailed recipe will resolve all those
> > unclear aspects.
> >
> > Thanks.

Can't reproduce example "seq..." with GNU Emacs 28.0.50 (build 1, 
i686-pc-linux-gnu, GTK+ Version 3.14.5, cairo version 1.14.0) of 2020-06-10