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: Michael Albinus <michael.albinus@gmx.de>,  suhailsingh247@gmail.com,
>   73046@debbugs.gnu.org
> Date: Sun, 08 Sep 2024 12:46:39 -0400
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Waiting for a process to respond should try not to spin without
> > sleeping for a few milliseconds between polling attempts.
> 
> A constant delay busy-wait would be better than what's there today.

It isn't a delay, or at least the delay is not the main point.  The
main point is to yield the CPU, and that usually has dramatic effect
on CPU load.

> However, I thought you'd be proposing something like registering a
> "callback".  Out of curiosity, since I am unfamiliar with the relevant
> Emacs internals, would it not be possible to add a function to the
> equivalent of `after-change-functions' that processes the output?

accept-process-output already does that.  Except that with a timeout
of zero, it just checks whether any output arrived, and if not,
returns immediately.  Adding a timeout will AFAIU cause us to let the
OS preempt our execution thread and reschedule it only if no output
arrives during the timeout.