Re: MPS: profiler

[Eli Zaretskii <eliz@gnu.org>]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: Eli Zaretskii <eliz@gnu.org>, eller.helmut@gmail.com, emacs-devel@gnu.org
> Date: Fri, 21 Jun 2024 20:02:42 +0000
> 
> Gerd Möllmann <gerd.moellmann@gmail.com> writes:
> 
> > Ihor Radchenko <yantar92@posteo.net> writes:
> >
> >> Now, the question is whether the profiler output wrt "Automatic GC" on
> >> scratch/igc branch represent the moments when Emacs is being properly
> >> frozen.
> >
> > Simply said no.
> 
> Then, we should probably not record the times when MPS is active as
> "Automatic GC" in the profiler. Maybe simply skip these samples for the
> time being (with a FIXME in the code)? That would be more accurate.

I don't think I agree.  We might rename "Automatic GC" to something
more accurate, but skipping that will cause the percentage to be
skewed.  By and large, this is just about the interpretation of that
percentage, nothing else.

In any case, you are worrying about these minor issues too early.  We
are nowhere near a point where they matter.  For now, we need to make
sure the basic features of Emacs work reliably without crashing; the
accuracy of their results comes much later.  Let's not put the
proverbial wagon before the horse and waste time discussing issues
which are for now largely theoretical.

> > MPS telemetry could perhaps be used, not sure, and it would of course
> > need someone to do it :-).
> 
> We will eventually need some kind of telemetry to compare traditional GC
> vs. MPS.

Just start Emacs, visit xdisp.c, and scroll through it by leaning on
C-v, and you will immediately see how much faster this GC is.  (You
can also run 'top' or something similar simultaneously to see how the
memory footprint grows and then goes down, while you scroll.)  So
let's please not worry about what the profiler says about GC, because
the answer to your question is abundantly clear without that already.