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

[Clément Pit--Claudel]

On 2017-03-12 11:49, Eli Zaretskii wrote:
>> Cc: 21028@debbugs.gnu.org
>> From: Clément Pit--Claudel <clement.pitclaudel@live.com>
>> Date: Sun, 12 Mar 2017 07:38:13 -0400
>>
>> Any news on this?
> 
> Not yet, sorry.  Having to install an OS is a bug turn-off for me.  I
> will try reproducing on my system with the font you mentioned.

I see. What about downloading a pre-built virtual machine, or running a Vagrant 
script?  Would any of these work better?

>> Is there anything more than I can do to help fix this issue?
> 
> If you can come up with a recipe that doesn't require a particular OS
> and font back-end, it will help a lot.

The last steps of the recipe reproduce the problem reliably on my machine, 
assuming Ubuntu Mono (http://font.ubuntu.com/) and XITS Math 
(https://github.com/khaledhosny/xits-math) are installed:

$ time src/emacs -Q --eval "(progn (set-fontset-font \"fontset-startup\" 
'unicode \"Ubuntu Mono\" nil) (set-fontset-font \"fontset-startup\" 'unicode 
\"XITS Math\" nil 'append) (dotimes (_ 500) (insert (make-string 20 8658) 
\"\n\") (run-with-idle-timer 0 nil #'kill-emacs)))"
real    0m1.503s
user    0m0.540s
sys     0m0.244s

$ time src/emacs -Q --eval "(progn (set-fontset-font \"fontset-startup\" 
'unicode \"Ubuntu Mono\" nil) (dotimes (_ 500) (insert (make-string 20 8658) 
\"\n\") (run-with-idle-timer 0 nil #'kill-emacs)))"
real    0m0.473s
user    0m0.216s
sys     0m0.040s

# With your latest patch
$ time emacs -Q --eval "(progn (set-fontset-font \"fontset-startup\" 'unicode 
\"Ubuntu Mono\" nil) (set-fontset-font \"fontset-startup\" 'unicode \"XITS 
Math\" nil 'append) (dotimes (_ 500) (insert (make-string 20 8658) \"\n\") 
(run-with-idle-timer 0 nil #'kill-emacs)))"
real    0m0.382s
user    0m0.252s
sys     0m0.020s

In fact, on my machine, I get consistent results (unusably slow Emacs) 
regardless of whether I pick XITS Math, Symbola, or Latin modern Math (on all 
of 24.4, 24.5, and 25.1, but not on 24.3 of course), and your patch solves the 
problem perfectly in all of these cases (amusingly, on 24.3, 24.4, and 24.5, I 
also get the very tall lines if I use Latin Modern, but that problem is solved 
in 25; thanks again!).

Let me know if I can help further!  I can also give you remote access to a 
machine displaying the problem, if that helps.

Cheers,
Clément.

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