bug#28795: 25.2; UTF-8 language environment causes extreme sluggishness

[Mark Laws]

On Thu, Oct 12, 2017 at 7:00 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> [Please keep the bug address on the CC list.]

Sorry, mashed the wrong key.

> And which font is used if you don't set your language-environment to
> UTF-8?

uniscribe:-outline-Malgun
Gothic-bold-normal-normal-sans-15-*-*-*-p-*-ksc5601.1987-0 (#xF7)

>> > As another thing to try, set inhibit-compacting-font-caches to a
>> > non-nil value, and see if that helps.
>>
>> This seems to help
>
> By "this" do you mean installing Symbola or setting
> inhibit-compacting-font-caches non-nil?

(setq inhibit-compacting-font-caches t) seems to help. I did not try Symbola.

>> though the fact it only happens due to changes with encoding and/or
>> font locking makes me suspicious.
>
> It could be that the default language-environment causes a different
> font to be used for that character.

If I use (prefer-coding-system 'utf-8), I do not get the slowness
anymore, even if inhibit-compacting-font-caches is nil, and even after
propertizing the text. However, the font changes from PragmataPro Mono
to Malgun Gothic, which seems odd too.

if I use both (set-locale-environment "English") and
(prefer-coding-system 'utf-8), the issue returns.

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