bug#17837: 24.4.50; Search very slow

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> I counted around 45 seconds before it found the second occurrence.

Richard, was that in an "emacs -Q"?

> For me, the first one is slower: about 5 to 6 sec.  The second
> occurrence takes maybe 3.  Stefan, what's your timing?

Again trying it on my AMD E-350 machine, using the emacs-24 branch built
with -Og and enable-checking (on Debian testing), I get about half of
your times (about 2-3s for the first search and barely more than 1s for
the second).

Opening the file and doing M-> took 6s.
`emacs23' (Debian's build, i.e. probably with -O2 and without
enable-checking) took 4s for the M-> test.

On my fit-pc2 (Intel Atom, 1G RAM), the emacs-24 branch took 8s to do
the M->.
And on my Mele A2000 (i.e. Allwinner 1GHz A10 CPU with 512M of RAM), it
took 18s.

> Anyway, you may wish to experiment with setting jit-lock-defer-time to
> a non-nil value.  E.g., try setting it to 0.25 or 0.5 sec, and see if
> that gives good results.

I think we should first try and figure out why his second search takes
45s instead of a couple seconds (I expect his Longsoon might be slower
than my Atom, but not significantly slower than my little ARM machine).


        Stefan