Emacs 21.0.91 slowness in term mode

[Marco Melgazzi]

Hello 

after seeing a message posted in comp.emacs, I downloaded the 21.0.91
pretest in order to see what was brewing for the next emacs
version. Besides submitting a bug and a fix to pretest-bugs, I would
like to inquire about possible slowdowns in the new code.

While I am by no means an emacs newbie (I've been using it for many
years and also have some code of mine in the distribution) I've never
formally partecipated in the testing of new emacs versions, so if this
is the wrong forum to post in, I apologize.

Despite disabling the debugging define GC_CHECK_STRING_BYTES in alloc.c,
I am seeing vastly reduced performance in a crucial (for me) emacs area,
which is the terminal mode (term.el). I was wondering if this is due to
some other debugging code in this pre-test, or if it's something else.

I am comparing a precompiled 20.7 that shipped with my Redhat 7
GNU/Linux system, to the aforementioned self compiled 21.0.91. The code
has been compiled with -O3 -fomit-frame-pointer and with the said
debugging define disabled. Both emacsen have been launched with
--unibyte (even if it doesn't seem to make any difference in the 21
pretest whether this is on or off)

Method of testing was to just simply open an M-x term buffer, go to
/usr/bin, do a couple of ls -alg --color to fill the scrollback buffer
to capacity, and then to time some further ls -alg --color commands and
taking the average time.

              TTY no-init-file  TTY    X
Emacs 20.7       4.5            5.3   9.2
Emacs 21.0.91    7.5            8.7  13.3

As you can see, there is quite a deterioration in the new Emacs 21,
interestingly, the differential between the two measurements is fairly
costant, whether we are in X or TTY.

While I didn't run other tests, while scrolling around big files
etc. e20 always seemed much snappier than e21: also, if you go in a term
buffer and just keep the enter key depressed, e20 is much much more
responsive than e21 (when you stop pressing the key in e21 it takes more
time for the display to stop scrolling).

If you have any more questions on my configuration and/or would like me
to run some more tests, please do email me back, as having a speedy term
mode is absolutely essential for me, emacs being practically my login
shell ;)

Cheers !

Marco