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Re: Unbearably slow editing in .h files
From: |
Dan Nicolaescu |
Subject: |
Re: Unbearably slow editing in .h files |
Date: |
Thu, 03 Apr 2008 08:22:10 -0700 |
Alan Mackenzie <address@hidden> writes:
> On Thu, Apr 03, 2008 at 06:10:40AM -0700, Dan Nicolaescu wrote:
> > Alan Mackenzie <address@hidden> writes:
>
> > > On Wed, Apr 02, 2008 at 04:47:52PM -0700, Dan Nicolaescu wrote:
>
> > > > Alan Mackenzie <address@hidden> writes:
> > > > > I have just fixed this problem (I hope!) in both the Emacs-22
> > > > > branch and the trunk. Basically, the contorted functionality
> > > > > in add-log.el has been superseded by optimised routines in
> > > > > cc-cmds.el.
>
> > > > > On my 1.2 GHz Athlon machine, C-x 4 a now takes around 4
> > > > > seconds at the end of lisp.h, in the trunk. It's somewhat
> > > > > faster in the Emacs-22 branch, but I don't know why.
>
> > > > > I think this is fast enough.
>
> > > > Can it be faster? Might sound like a joke, but it's a serious
> > > > question.
>
> > > Just to clarify, that 4 seconds is in the extreme case (lisp.h)
> > > that brought the problem to light. In a typical case, the action
> > > is "instantaneous". When finding (or failing to find) a function
> > > name, the new implementation is more than an order of magnitude
> > > faster than the old. For a macro name, it takes about as long as
> > > the old.
>
> > > > `diff-add-change-log-entries-other-window' uses this (calls it
> > > > once per diff hunk), and it is nice to let it run on largish diff
> > > > buffers to quickly produce a skeleton for a ChangeLog .
>
> > > Hey, I didn't know you could do this. Thanks for telling me! :-)
> > > (Actually, until I looked at this bug report, I didn't realise you
> > > could do C-x 4 a in an elisp or C file - I thought it would only
> > > work when done in ChangeLog itself.)
>
> > Note that `diff-add-change-log-entries-other-window' is C-x 4 A not
> > C-x 4 a, it is the equivalent of:
> > FOR each hunk in a diff DO
> > C-x 4 a
>
> Wow! I've just tried this. It's amazing! There are one or two things
> in it which aren't quite right, though.
Yep, it should not generate duplicate entries.
One possible improvement is that it should iterate at a lower
granularity than a hunk, some hunks have changes ! + and - changes.
(but that's still not enough, a + hunk could be adding 5 functions...)
> > When used on a diff buffer with thousands of lines, it is a bit slow.
>
> Hmmm. I've only tried it on diffs with elisp files. That was a little
> slow. Do you mean it's _very_ slow with C file diffs? Can you give some
> numbers here? Processor speed, size of diff file, time it takes.
Unfortunately I don't have any massive patches handy, so I can't test
now how much things have improved for exactly the things that had
problems before. But some quick tests with the diff for lisp.h revision
1.606 (i.e. something that had a long ChangeLog entry, 625 lines
unidiff) showed that things have improved quite a lot today vs a > 1
month old emacs (a few seconds vs > 2 minutes).
Which is great. Thanks!
Trying C-x 4 A on a 4-5000 lines patch would be more interesting...
> But then again, people are only going to be using it once or twice
> per patch (and then having to fill out the result by hand), so it is
> surely not that critical. But if it were taking 20 minutes rather
> than 45 seconds, that would be too slow, I agree.
Ideally in the future C-x 4 A should be done automatically when doing a
checkin, that why it is important to be as fast as possible.
> > > > Is the slowdown still caused by the fact that is hard to
distinguish a
> > > > K&R functions from variable declarations?
>
> > > Again, it's a massive speedup, not a slowdown. Isn't it?
>
> > Sorry, I was referring to the fact slowdown cause by K&R checks, not
> > your patch.
>
> I'd be very interested to here how much faster C-x 4 A has become as a
> result of this patch and my patch on Friday 2008-03-07 to cc-engine.el.
See above.
> > > To the extent that it's still slower than it might be, yes it's the
> > > K&R stuff making it slow. The function which takes time is
> > > c-in-knr-argdecl (cc-engine.el, ~L6317). Actually, this function
> > > gets called twice. It would take a lot of refactoring to make it
> > > get called only once.
>
> > What if it's not called at all? After all, the vast majority of the
> > users never edit K&R. Just a thought...
>
> Well, one set of users who still use K&R is the Emacs development team.
> ;-)
Yeah, and many people wish that would change at some point. But that a
separate discussion that we should get into now.
> It would be possible, and very easy, to make K&R a user option. But
> I don't think that's the right thing to do.
>
> The overhead that K&R imposes on C-M-a and C-x 4 a is not _that_ high,
> and it will diminish as processors continue to get faster. I recently
> put in a hard-coded limit to the number of parameter declarations in a
> K&R section. That limit is currently 20.
Just exploring options here...
Would simply ignoring K&R for the purpose or running C-x 4 a work?
Yes, it might generate the wrong name in the ChangeLog entry in some
very limited cases (is that true?), but that's not very critical.