Re: Time to merge scratch/correct-warning-pos into master, perhaps?

[Alan Mackenzie]

Hello, Lars.

On Sat, Feb 05, 2022 at 07:08:16 +0100, Lars Ingebrigtsen wrote:
> Gregory Heytings <gregory@heytings.org> writes:

> > I attach the detailed results for each of the 389 tests.  Each test
> > has been executed 2000 (two thousand) times, again on an unloaded
> > up-to-date Debian bookworm computer.

> [...]

> > If you remove that test from the calculations, you will see that the
> > slowdown is actually 17%, that is, the same slowdown as that of byte
> > compilation.

> Thanks, that's interesting, but it doesn't really answer the question of
> why it's so hard to see these performance regressions in actual use.  I
> tried to benchmark Alan's patches before they went in by doing things
> like measuring shr DOM rendering, and saw essentially no measurable
> difference.  And 17% vs "essentially nothing" is a big gap.

> So it's still not clear what's being measured.  Is ert doing something
> that's triggering these slowdowns?  Is it only measurable in "emacs
> -batch"?  Is there something else that makes the test suites so much
> slower while we're not seeing that in real usage?

I just tried to disassemble an ert-form for (ert-deftest
parse-partial-sexp-paren-comments () ...), in tests/src/syntax-tests.el.
I haven't yet managed it, but just dumping (get
'parse-partial-sexp-paren-comments 'ert--test) onto the *Messages*
buffer, it is apparent that symbols with position have somehow got into
the compiled form.  They appear like this:

\312\313^B\301\"D\262^A\244\240\210\314\303\242!\207" [V0 V1 V2 V3 (should 
(#<symbol = at 3586> (#<symbol nth at 3589> \

..  This might have something to do with the slowdown, it might not.  But
there is definitely a bug somewhere to fix.  I don't know yet whether
these dumped forms actually get executed, or whether they're just there
to be displayed on an error.  If they do get executed, the SWP there
might explain the slowdown in the tests.

> -- 
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no

-- 
Alan Mackenzie (Nuremberg, Germany).