Re: slow output in *compilation* buffer

[David Kastrup <dak@gnu.org>]

Stefan Monnier <monnier@IRO.UMontreal.CA> writes:

>>> - the re_* part of the profile is hard to improve with a quick fix,
>>> I think: it just represents regexp-searching every one of the regexps
>>> in compilation-error-regexp-alist in turn.  Of course, there is a way
>>> to do that (a lot) faster, by compiling all those regexps into a DFA.
>> That sounds like a good idea, but it does not look like it will have a
>> huge impact?
>
> No, indeed, luckily.
>
>>> - why does the gprof data only seem to account for a bit less than 10s
>>> when you say it takes 25s to complete?
>> Don't know.  I double checked and it's consistent.  Maybe oprofile can
>> reveal more, I might try that too when I get a chance  if nobody  beats
>> me to it.
>
> Maybe it's just the user-time vs system-time.
>
>>> - It seems that they the calls to the interval code come from
>>> compilation-error-properties, but that function should only be called
>>> for regexps that do match, which shouldn't be that many.  Can you look
>>> at the text to see if there really are that many matches?  BTW, we
>>> should probably be able to make compile.el a bit lazier (i.e. the
>>> font-lock-phase part of the code should do a bit less work by moving
>>> it to the next-error-phase code).
>> The output is about 4500 lines, they all match.
>
> Ah, I see.  So yes, the likely solution is to make compile.el lazier:
> use font-lock-syntactic-keywords and jit-lock (so the text past the end
> of the window doesn't need to be scanned right away), and postpone more
> of the work to next-error.
>
>> BTW, doing the same search with M-x rgrep is MUCH MUCH slower.
>
> That sucks.  What does rgrep do so differently to make it even worse?
>
>> They time spent there seems a bit excessive, so maybe something strange
>> is going on...
>
> That's also possible.

Does

(setq process-adaptive-read-buffering nil)

make a difference?  I have the suspicion that this still exhibits
pathological behavior sometimes.

-- 
David Kastrup