bug#21028: Performance regression in revision af1a69f4d17a482c359d98c00ef86fac835b5fac (Apr 2014).

[Clément Pit--Claudel]

On 2017-03-13 13:22, Eli Zaretskii wrote:
>> Cc: 21028@debbugs.gnu.org From: Clément Pit--Claudel
>> <clement.pitclaudel@live.com> Date: Mon, 13 Mar 2017 12:36:25
>> -0400
>> 
>> On 2017-03-13 11:46, Eli Zaretskii wrote:
>>> I installed Fira Sans and Noto Sans, and changed your program to
>>> insert more of these characters and actually display all the
>>> characters it inserts (see below).
>> 
>> Thanks, that's a much better repro than mine :) Here are my
>> timings:
>> 
>> # Stock 24.5 12:01:26 /build/emacs $ time 24.5/src/emacs -Q --eval
>> "(progn (set-fontset-font \"fontset-startup\" 'unicode \"Noto
>> Sans\" nil) (set-fontset-font \"fontset-startup\" 'unicode
>> \"Symbola\" nil 'append) (dotimes (_ 5000) (insert (make-string 20
>> 8658) \"\n\")) (goto-char (point-min)) (sit-for 0) (condition-case
>> nil (while t (scroll-up) (sit-for 0)) (error nil))
>> (run-with-idle-timer 0 nil #'kill-emacs))" real      1m1.862s user
>> 0m18.644s sys        0m15.972s
>> 
>> # Stock 25.1 $ time 25.1/src/emacs -Q --eval "(progn
>> (set-fontset-font \"fontset-startup\" 'unicode \"Noto Sans\" nil)
>> (set-fontset-font \"fontset-startup\" 'unicode \"Symbola\" nil
>> 'append) (dotimes (_ 5000) (insert (make-string 20 8658) \"\n\"))
>> (goto-char (point-min)) (sit-for 0) (condition-case nil (while t
>> (scroll-up) (sit-for 0)) (error nil)) (run-with-idle-timer 0 nil
>> #'kill-emacs))" real 1m4.705s user   0m18.296s sys   0m18.444s
>> 
>> # Master with your patch $ time master/src/emacs -Q --eval "(progn
>> (set-fontset-font \"fontset-startup\" 'unicode \"Noto Sans\" nil)
>> (set-fontset-font \"fontset-startup\" 'unicode \"Symbola\" nil
>> 'append) (dotimes (_ 5000) (insert (make-string 20 8658) \"\n\"))
>> (goto-char (point-min)) (sit-for 0) (condition-case nil (while t
>> (scroll-up) (sit-for 0)) (error nil)) (run-with-idle-timer 0 nil
>> #'kill-emacs))" real 0m1.207s user   0m0.928s sys    0m0.028s
> 
> I see nothing of the kind, as you saw.  With the same fonts as you 
> use.  So it's definitely not a problem with the fonts.  Which is 
> strange, since the profiles you provided seem to indicate a 
> font-related problem.

We know the exact commit that caused this regression, right?  So how could the 
problem not be font-related, since reverting it fixes the problem?

> So why not use Symbola (i.e. the default fontset setup)?

Because I don't use Symbola proper, but a monospacified variant.  In fact, I 
use XITS Math (monospacified) now, followed by Symbola as the fallback.
And in any case, we're not just trying to fix my problem: I regularly get 
support requests about company-coq because people run into performance issues 
with Emacs and prettify-symbols-mode. 

> Symbola supports emoji in the default fontset, so neither Segoe UI 
> nort Symbola should be needed in your setup.

Except I don't want the Emoji from Symbola — I want the ones from Segoe.  And 
again, this isn't about fixing my setup (I've perfectly happy running my 
self-compiled fork for the last year-and-a-half).

> As for Ubuntu Mono, isn't that the default monospaced font?

Not on all my machines, no.

> In short, are you sure you really need those customizations?  You
> may be creating your own problems.

I'm sure: commit af1a69f4d17a482c359d98c00ef86fac835b5fac is creating my 
problems :)

> The default fontset should already provide you with the fonts that 
> display all of these, including CJK.  If you use the default, what 
> characters aren't displayed well enough, or at all?

Depends on the machine: not well enough on some, not at all on other, depending 
on the installed set of fonts.

> Is this the complete fontset setup you are using […] If it is, I will try to 
> reproduce using this fontset.

No, not exactly.  The full thing is at 
https://github.com/cpitclaudel/.emacs.d/blob/master/init/fonts.el#L7, but the 
problem is reproducible in a clean install an a much simpler set up.

What about the VM approach, or simply remote access on a VM that I could 
provide? I'm afraid that you'll waste your time reproducing my complex set-up, 
with no actual benefit.  Do you want to reproduce the problem to debug it 
locally, or something else? If the former, it there nothing I could do to help?

Would it help if I tried to find other people who can reproduce the problem on 
their machines by following my VM-based reproduction steps?

Cheers,
Clément.