From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Dmitry Gutov Newsgroups: gmane.emacs.bugs Subject: bug#56682: Fix the long lines font locking related slowdowns Date: Wed, 10 Aug 2022 21:54:04 +0300 Message-ID: References: <83h72qzheq.fsf@gnu.org> <25717d84-3411-a93a-3620-e04fe0571aff@yandex.ru> <83edxuzemr.fsf@gnu.org> <83a68hzz0a.fsf@gnu.org> <6ae35c93062c589b2e02@heytings.org> <7b7fbad7-55ac-49b8-840f-7f89a7e8771a@yandex.ru> <6ae35c93064b3588974c@heytings.org> <6ae35c9306c515f420d8@heytings.org> <87k07gwkjq.fsf@gmx.net> <87fsi4wiel.fsf@gmx.net> <837d3gs4p0.fsf@gnu.org> <83tu6kqnf1.fsf@gnu.org> <83fsi4qdxp.fsf@gnu.org> <2aa80c8f-5fb8-1892-72cd-60f050261104@yandex.ru> <838rnwqami.fsf@gnu.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="28049"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Mozilla/5.0 (X11; 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Wed, 10 Aug 2022 11:54:05 -0700 (PDT) Content-Language: en-US In-Reply-To: <838rnwqami.fsf@gnu.org> X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.io gmane.emacs.bugs:239315 Archived-At: On 10.08.2022 20:19, Eli Zaretskii wrote: >> Date: Wed, 10 Aug 2022 20:02:20 +0300 >> Cc: 56682@debbugs.gnu.org, gregory@heytings.org, stephen.berman@gmx.net, >> monnier@iro.umontreal.ca >> From: Dmitry Gutov >> >> It's much worse. In the aforementioned dictionary.json, with >> fully-featured font-lock (narrowing disabled in handle_fontified_props) >> the buffer is perfectly responsive to edit as long as I (setq >> bidi-inhibit-bpa nil). Even with show-paren-mode enabled. >> >> Without that, however, simple navigation commands take a significant >> amount of time. These measurements are with show-paren-mode off: >> >> Near BOB: >> >> (benchmark 1 '(next-line 1)) => >> Elapsed time: 0.246551s >> Elapsed time: 0.247237s >> Elapsed time: 0.247392s >> >> Near EOB: >> >> (benchmark 1 '(next-line 1)) => >> Elapsed time: 0.059583s >> Elapsed time: 0.040372s >> Elapsed time: 0.059508s > > That's what I meant: it isn't a catastrophe. 1/4th of a second for > C-n is barely perceptible. It's 2.5 the upper limit on what's perceived as "instant". And it's higher than the "uncomfortable" font-lock delays I have seen. > "Catastrophe" in my book is when it takes more than a couple of > seconds, like 10 sec or more. For such a basic operation as next-line, it seems excessive to me. But if you're sure about this, all right. This delay doesn't seem to extend to other commands, such as C-f/C-b or self-insert-command. It does seem to affect isearch, though. >>> not >>> like we've seen with the files we used for the long-lines speedups. >>> And if someone does think it's a catastrophe, they can always disable >>> the BPA, perhaps even globally, >> >> That reminds me of "the user can always disable font-lock" and your >> dismissal of Alan's advice to change font-lock-maximum-decoration to 2, >> saying that we should have good editing performance OOTB. > > No, because font-lock is much more important than the effect of the > BPA. (Do you even understand what the BPA does, and did you ever see > it in action? Without that, this part of the discussion is just waste > of time.) I have looked at examples now. Seems important for text in pertinent human languages. >>> if they know they will never need to >>> look closely at bidirectional text: the effects are hardly visible >>> unless you actually read the text. >> >> We could add (setq bidi-inhibit-bpa nil) to prog-mode, I suppose. > > Not to prog-mode, that I won't agree. But maybe for JSON files, if we > think they are unlikely to suffer. Sure, maybe. Where do we draw the line, though? Not in prog-mode because a .js file, say, can have comments in Persian or Hebrew? By that measurement, JSON is fine (no comments supported). But JSON contains a bunch of strings, could store localizations, etc. I suppose the contents of said strings can store i18n text, with the expectation of a user being able to edit it. >> It already has a bidi-paragraph-direction setting anyway. > > That's not even similar. That's just saving Emacs to figure that out > itself, wasting CPU cycles on what is known in advance. Because a PL > buffer _always_ has its paragraphs left-to-right. > >>> This is impossible without a complete redesign of how the bidi display >>> works: it saves no information in the buffer object, none whatsoever. >>> The information is recomputed every time the display code is called, >>> and only for the portion of the buffer that needs to be traversed or >>> displayed; then it is discarded. There are no caches of any kind that >>> keep the information after redisplay has done its job. >> >> Perhaps a cache similar to syntax-ppss one could do the job? Not sure >> what would be the trafeoffs, though. Like, how that would change the >> performance in the simple case. > > There are no caches for a good reason: the Unicode Bidirectional > Algorithm that we implement results in very far-reaching non-local > effects of small changes. Even inserting or deleting a single > character can dramatically change how the buffer looks on display very > far from the locus of the change. In both directions? > Figuring out which changes > invalidate which caches is extremely non-trivial, and in many cases > requires the same amount of work as would take to just recompute > everything from scratch. Sounds a little similar to syntax-ppss cache: changing a character near BOB invalidates the whole cache for all positions > POS. This one sounds more complex, though.