Re: Merging scratch/no-purespace to remove unexec and purespace

[Pip Cet via "Emacs development discussions." <emacs-devel@gnu.org>]

"Helmut Eller" <eller.helmut@gmail.com> writes:

> On Tue, Dec 17 2024, Stefan Kangas wrote:
>
> [...]
>> We, the maintainers, believe that the scratch/no-purespace branch is
>> now ready to merge, and would appreciate any final feedback, testing,
>> and code reviews.  Specifically, the branch has been primarily tested
>> on GNU/Linux and macOS, so testing on other systems would be greatly
>> appreciated.
>
> Do you have an estimate what removing purespace will cost in terms of GC
> time?  I mean something like "1ms per collection".  Or perhaps a
> suggestion how I could measure it?

"Close to zero" is the best I can do at this time.  In particular, that
implies "not catastrophically worse", which is all that is relevant
right now, IMHO.

> I mean something like "1ms per collection".  Or perhaps a
> suggestion how I could measure it?

I think that all the previously-pure data should be available right away
after starting an Emacs session, so maybe something like:

perf record -e cycles ./src/emacs -Q --batch --eval '(dotimes (i 1000)
(garbage-collect)))'

would be one data point.  Some effects would only be visible in GCs with
deep call stacks, or in large sessions, but that's hard to measure.

Pip