To clarify, I was not writing to a file that was open in emacs.  In fact,
emacs would use 100% cpu even with no files opened, so long as
global-auto-revert-mode was activated.

On Tue, Oct 30, 2018 at 2:22 AM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Justin Van Winkle <justin.vanwinkle@gmail.com>
> > Date: Mon, 29 Oct 2018 17:13:22 -0400
> > Cc: 33194@debbugs.gnu.org
> >
> > It was outside of emacs.  SCP would trigger the cpu usage in emacs,
> rsync would not (oddly).  Both "cat
> > /dev/zero > somefile"  and "dd if=/dev/zero of=somefile" would trigger
> it if somefile was in my $HOME
> > directory, but none of these would trigger it if I did it in, for
> example, $HOME/Downloads/
>
> Isn't this expected?  Auto-revert watches the directory of the file,
> so if a lot of changes happen in that directory, Emacs will get a lot
> of file-change notifications, and will need to process them.
>
> If you don't like this, customize auto-revert-use-notify to not use
> notifications.  Or maybe there's some system-wide customization of
> inotify that determine the max frequency of inotify notifications when
> the changes are to the same file.  (I don't know enough about inotify
> to say anything more specific, sorry.)
>