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Re: Emacs 23.0 is much slower starting than Emacs 22.3

From: David De La Harpe Golden
Subject: Re: Emacs 23.0 is much slower starting than Emacs 22.3
Date: Fri, 24 Oct 2008 15:32:30 +0100
User-agent: Mozilla-Thunderbird (X11/20081018)

Alan Mackenzie wrote:

However, the current function isn't that slow.  I timed it for 100
iterations on a file 2,927,889 bytes big.  It's taking 0.72s for this
file, i.e. about 0.25s per megabyte, and that's on my 1.2 GHz Athlon.

So on emacs/src's 118 files.c, total size 8772802, that function would
take only 2.5s, again, on my Athlon.  On your machine it would be ~0.5s.

Besides, in my original measurements, I was executing the same CC Mode
in Emacs 22 and Emacs 23.

c-neutralize-syntax-in-CPP isn't the problem.

Probably not, or at least not the slowdown you're seeing i.e. your relative emacs22/23 problem. N.B. It wasn't intended as a slight - I do appreciate C is a relative pain to parse, syntax-highlight and deal with in general, I'm_ not_ saying c-mode's apparently associated overhead is necessarily unreasonable, but it may explain why stuff I was generally doing in emacs day-to-day seemed to load a little bit faster than this particular test case (if you recall, I was surprised at the result) - I relatively seldom edit c files! But c-mode as a whole _does_ account for a significant chunk of the startup time on the 180 .c files I was testing with:

time emacs -l fftest.el -f kill-emacs
with in .emacs  a sneaky
(setq auto-mode-alist (cons (cons "\\.c\\'" 'text-mode)       auto-mode-alist))

emacs c-mode    realtime
22      on      4.951
23      on      7.388
22      off     2.830
23      off     4.089

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