[libvirt] [PATCH v4 00/26] scripts: convert most perl scripts to python

[Ján Tomko]

On Wed, Oct 09, 2019 at 12:37:15PM +0100, Daniel P. Berrangé wrote:
>Note that the check-spacing.py script is significantly
>slower in Python than in Perl. After researching this
>it appears there is nothing that can be done. The Perl
>regex engine is simply much better optimized than the
>Python one.

I'm afraid immutability of strings does not help either.
I tried speeding it up a bit by running the regexes conditionally, e.g.:

+            if '"' in data:
+                data = quotedstringprog.sub('"XXX"', data)

That got it down from 0m6.368s to 0m3.802s (compared to perl's 1.5s),
but even before that change, I don't consider the Python version of this
one script to be more readable.

Note that perl's optimizations aren't perfect either - merely
moving all the checks into a subroutine resulted in a significant
slowdown.

>As previously discussed we need to loook
>at uncrustify or clang-format or some other tool to
>validate whitespace formatting. This is ongoing. We
>can either accept the slow down in the short term or
>keep the Perl version in the short term.
>

Just to set the expectations, running clang-format on all the
C files took me ~40 s. Not sure how much that can be efficiently
parallelized or if meson could be convinced to start clang-format
as the first thing for the 'check' target, even before starting
to compile anything.

Jano
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