bug#10835: 24.0.93; bidi-paragraph-direction slows down Shell mode

[Chong Yidong]

I just noticed that when I do `ls --color=no' rather than just `ls',
insertion and scrolling are very fast.  The sluggishness only appears
when ls color highlighting is enabled.  So the inefficiency of
ansi-color.el, and its use of overlays, seems to play a role.


Eli Zaretskii <eliz@gnu.org> writes:

> What does "time ls /usr/share/doc" say, when you run it from the shell
> buffer?  What are the times it reports, and are they approximately the
> same in each of the 4 invocations?

Times are below.  Another observation: with `time ls /usr/share/doc'
(which does use color highlighting), scrolling through the Shell buffer
is no longer sluggish.  I think the output of `time' helps by providing
a paragraph break.

If I do plain `ls' (no `time'), then go back and edit the Shell buffer
manually by adding a C-q C-j line break after each prompt, that also
makes the scrolling sluggishness go away.

In xterm (speed is the same after repeated invocations):

real    0m0.148s
user    0m0.008s
sys     0m0.020s

In xterm, with --color=no:

real    0m0.039s
user    0m0.004s
sys     0m0.008s

In the Emacs 23 shell buffer, on the first invocation:

real    0m0.378s
user    0m0.008s
sys     0m0.008s

In the Emacs 24 shell buffer, on the first invocation:

real    0m0.866s
user    0m0.008s
sys     0m0.004s

In the Emacs 24 shell buffer, after 10 invocations:

real    0m1.969s
user    0m0.008s
sys     0m0.004s

In the Emacs 24 shell buffer, with --color=no:

real    0m0.296s
user    0m0.000s
sys     0m0.008s

In the Emacs 24 shell buffer, with --color=no, after 10 invocations:

real    0m0.280s
user    0m0.004s
sys     0m0.012s