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bug#61779: 30.0.50; excessive redisplay when the mini window is active
From: |
Po Lu |
Subject: |
bug#61779: 30.0.50; excessive redisplay when the mini window is active |
Date: |
Sat, 25 Feb 2023 17:37:14 +0800 |
User-agent: |
Gnus/5.13 (Gnus v5.13) |
Eli Zaretskii <eliz@gnu.org> writes:
>> Date: Sat, 25 Feb 2023 14:16:37 +0800
>> From: Po Lu via "Bug reports for GNU Emacs,
>> the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>>
>> For some reason redisplay_internal will always update the mini window
>> even if its buffer contents have not changed. I guess there is probably
>> a missing optimization wrt to updating the echo area contents, and
>> window_outdated does not take the echo area message into account:
>>
>> && (CHARPOS (tlbufpos) == ZV
>> || FETCH_BYTE (BYTEPOS (tlbufpos)) == '\n'))
>> /* Former continuation line has disappeared by becoming empty. */
>> goto cancel;
>> else if (window_outdated (w) || MINI_WINDOW_P (w)) <==============
>> {
>> /* We have to handle the case of continuation around a
>> wide-column character (see the comment in indent.c around
>> line 1340).
>>
>> I am not sure that is why, however, so I can't just change that.
>> Anyway, update_window_line does not draw anything since the contents of
>> the glyph row do not change after redisplay, so that part is fine. The
>> problem is that the redisplay will lead to update_window being called,
>> and gui_update_window_end will always call display_and_set_cursor
>> afterwards to display the cursor, which is not okay, as it generates a
>> lot of X protocol traffic when redisplay is called and redisplays the
>> mini-window. Now add to that a process generating a lot of output, and
>> by doing so, calls to redisplay_preserve_echo_area, and you have an
>> absurd number of X requests, enough to saturate any reasonable network
>> connection.
>>
>> Here is a patch to resolve the problem by not redrawing the cursor when
>> Emacs knows it is already there. I've not seen any ill effects so far,
>> but the comment originally there seems to know better, so what are the
>> cases where ``phys_cursor_on_p is 1 but the cursor has been erased''?
>
> This is okay for master, thanks.
The comment that was there still makes me uncomfortable, so:
> Btw, the code which tests MINI_WINDOW_P here:
>
>> && (CHARPOS (tlbufpos) == ZV
>> || FETCH_BYTE (BYTEPOS (tlbufpos)) == '\n'))
>> /* Former continuation line has disappeared by becoming empty. */
>> goto cancel;
>> else if (window_outdated (w) || MINI_WINDOW_P (w)) <==============
>> {
>> /* We have to handle the case of continuation around a
>> wide-column character (see the comment in indent.c around
>> line 1340).
>
> is very old, dating back to the initial revision of xdisp.c before the
> Emacs 21 display engine changes, so maybe we should try removing that
> instead (assuming that it is related to the more general change
> regarding the cursor you want to install).
I guess that's the better idea, since it's the only reasonable way I
found to make update_window be called extremely often without any
changes actually happening.