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Re: master afc0bfd380: Speed up loaddefs-generate on slow disks

From: Eli Zaretskii
Subject: Re: master afc0bfd380: Speed up loaddefs-generate on slow disks
Date: Fri, 03 Jun 2022 16:05:19 +0300

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: larsi@gnus.org,  emacs-devel@gnu.org,  eggert@cs.ucla.edu
> Date: Fri, 03 Jun 2022 08:21:32 -0400
> >> This suggests that the kind of change I suggested would make it even
> >> a bit faster, tho it should reduce the run time by less than 50%
> >> under Windows (because the time to do the `stat`s is apparently already
> >> >50% of the total).
> >
> > I don't know how you deduce the 50% figure.
> The old code performed 2*N `stat`s.
> The new current code performs N times `time-less-p` and
> `file-attributes`, which is N `stat`s plus N times some overhead.
> The proposed new functionality would reduce this to more or less just
> N `stat`s so it would save us the "some overhead".
> Because the old code is slower than the current code, we know that
>     2*stat > stat + overhead
> thus `stat > overhead`.  So `overhead` is less than 50% of `stat + overhead`.

You evidently assume something about "the change you suggested",
because it is not just trivial modifications of what we do now: it
will have new "overhead" that is not part of the existing "overhead".

So it is still a guess in my eyes, and guesses related to CPU
profiles are many times wrong.

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