From: Olivier Scalbert <olivier.scalbert@algosyn.com>
To: "Alan Mackenzie" <acm@muc.de>, "Mattias Engdegård" <mattiase@acm.org>
Cc: 42490@debbugs.gnu.org
Subject: bug#42490: Emacs is very slow when navigating into a specific C++ file
Date: Fri, 24 Jul 2020 21:34:51 +0200 [thread overview]
Message-ID: <1b3a22e8-859f-b839-74cb-1905a8298b52@algosyn.com> (raw)
In-Reply-To: <20200724192450.GA8811@ACM>
Hi,
Thanks for your answer.
Unfortunately, I am out of my home, with no PC, for the week-end.
If I'll survive, I will test it next Monday. Very sorry !
;-)
Regards,
Olivier
On 7/24/20 9:24 PM, Alan Mackenzie wrote:
> Hello, Mattias and Olivier.
>
> Firstly Olivier, thanks for taking the trouble to report the bug.
>
> On Fri, Jul 24, 2020 at 18:46:45 +0200, Mattias Engdegård wrote:
>> Hello Olivier,
>> Thanks for the report! Could you try Emacs 27 (or git master), building
>> from source if necessary? Those versions should be slightly faster,
>> although the response time is probably well below acceptable.
>> If we distill the essentials of your file to some sort of benchmark, we
>> might end up with:
>> (with-temp-buffer
>> (c++-mode)
>> (dotimes (_ 1000)
>> (insert "OP(ed,b0) { ldir(); } /* LDIR */\n"))
>> (garbage-collect)
>> (let ((t0 (current-time)))
>> (font-lock-ensure (point-min) (point-max))
>> (time-to-seconds (time-since t0))))
>> Emacs 26.3 runs it in 11.9 s on this old lappy, but Emacs 27 does it in
>> 3.3 s. This is a clear improvement but we should be able to do better.
>> Alan may have a feeling for where the cycles are spent.
> I've bisected CC Mode to find the critical change, and it is:
>
> commit cc80eeb4a43d2079963de3d181002a6a6b56560d
> Author: Alan Mackenzie <acm@muc.de>
> Date: Fri Apr 12 20:07:03 2019 +0000
>
> Analyze C++ method with & or && ref-qualifier as defun, not brace list
>
> Also firm up detection of beginning of brace list in
> c-looking-at-or-maybe-in-bracelist.
>
> I have a simple benchmark which scrolls through a file, fontifying it,
> and my results from this benchmark are:
> (i) Before applying that patch: 53.022s.
> (ii) After applying that patch: 7.039s.
>
> I don't understand at the moment why that patch sped up scrolling in your
> (Olivier's) file, but it would seem the patch is most desirable.
>
> Unfortunately, the patch won't apply cleanly to the Emacs 26.3 sources.
> It might be possible to find a sequence of patches which would do the
> job. I think (though I haven't checked) the patch will have been
> included in the upcoming Emacs 27.1 release.
>
next prev parent reply other threads:[~2020-07-24 19:34 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-23 7:45 bug#42490: Emacs is very slow when navigating into a specific C++ file Olivier Scalbert
2020-07-24 16:46 ` Mattias Engdegård
2020-07-24 19:24 ` Alan Mackenzie
2020-07-24 19:34 ` Olivier Scalbert [this message]
2020-09-21 9:06 ` Alan Mackenzie
2020-09-21 17:29 ` Olivier Scalbert
2020-09-22 10:03 ` Alan Mackenzie
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