bug#61667: 29.0.60; Failure to redisplay

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Dmitry Gutov <dgutov@yandex.ru> writes:

> On 24/02/2023 17:51, Eli Zaretskii wrote:
>>> I just said that unchanging title doesn't stop me from seeing the delay
>>> when there is, in fact, a delay.
>> So, now, when does the delay happen?  I previously thought it happens
>> when the frame's title changes, but now you are saying it (and the
>> commit you mentioned) is unrelated, right?  Then what_is_  related?
>> Just the display-related activity in windows around Emacs?
>
> I press 'a' (which calls find-file) and see the delay between the
> keypress and the buffer being displayed.
>
> When the title format is a constant, the aforementioned delay is
> always instant/imperceptible. When the title format depends on the
> file name, the delay can be quite noticeable (randomly).

Judging by the symptoms you presented, this is likely some pathology in
Mutter (the GNOME compositor), and should be reported to them, not us.

I now think I know an easy way to test this theory for sure.  Create
another frame, place it so that it is above the frame you are trying to
test, set its Z group to above and its alpha-background parameter to
0.9, run some command that updates that frame once per second, and place
it above the first frame.

Then, see if the text inserted appears only once an update happens to
the other frame.  To be extra sure, run the other frame in another Emacs
process.

Thanks.