Re: [PATCH 06/18] chainlint.pl: validate test scripts in parallel

[Eric Sunshine <sunshine@sunshineco.com>]

On Mon, Nov 21, 2022 at 8:32 AM Ævar Arnfjörð Bjarmason
<avarab@gmail.com> wrote:
> On Sun, Nov 20 2022, Eric Sunshine wrote:
> > Somehow Windows manages to be unbelievably slow no matter what. I
> > mentioned elsewhere (after you sent this) that I tested on a five or
> > six year old 8-core dual-boot machine. Booted to Linux, running a
> > single chainlint.pl invocation using all 8 cores to check all scripts
> > in the project took under 1 second walltime. The same machine booted
> > to Windows using all 8 cores took just under two minutes(!) walltime
> > for the single Perl invocation to check all scripts in the project.
>
> I'd be really interested in seeing e.g. the NYTProf output for that run,
> compared with that on *nix (if you could upload the HTML versions of
> both somewhere, even better).

Unfortunately, I no longer have access to that machine, or usable
Windows in general. Of course, someone else with access to a dual-boot
machine could generate such a report, but whether anyone will offer to
do so is a different matter.

> Maybe "chainlint.pl" is doing something odd, but this goes against the
> usual wisdom about what is and isn't slow in Perl on windows, as I
> understand it.
>
> I.e. process star-up etc. is slow there, and I/O's a bit slower, but
> once you're started up and e.g. slurping up all of those files & parsing
> them you're just running "perl-native" code.
>
> Which shouldn't be much slower at all. A perl compiled with ithreads is
> (last I checked) around 10-20% slower, and the Windows version is always
> compiled with that (it's needed for "fork" emulation).
>
> But most *nix versions are compiled with that too, and certainly the one
> you're using with "threads", so that's not the difference.
>
> So I suspect something odd's going on...

This is all my understanding, as well, which is why I was so surprised
by the difference in speed. Aside from suspecting Windows I/O as the
culprit, another obvious possible culprit would be whatever
mechanism/primitives "ithreads" is using on Windows for
locking/synchronizing and passing messages between threads. I wouldn't
be surprised to learn that those mechanisms/primitives have very high
overhead on that platform.

> > Overall, I think Ævar's plan to parallelize linting via "make" is
> > probably the way to go.
>
> Yeah, but that seems to me to be orthagonal to why it's this slow on
> Windows, and if it is that wouldn't help much, except for incremental
> re-runs.

Oh, I didn't at all mean that `make` parallelism would be helpful on
Windows; I can't imagine that it ever would be (though I could once
again be wrong). What I meant was that `make` parallelism would be a
nice improvement and simplification (of sorts), in general,
considering that I've given up hope of ever seeing linting be speedy
on Windows.