bug#44175: [optimization] Grafting is too slow

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hello!

Ludovic Courtès <ludo@gnu.org> writes:

> Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:
>
>> Lars-Dominik Braun <ldb@leibniz-psychology.org> writes:
>>
>>> Hi Maxim,
>>>
>>>> Judging from the above, it seems this issue has been resolved.
>>> grafting is still a performance issue imo. Compare for example:
>>>
>>> $ time guix environment --ad-hoc  --search-paths r-learnr
>>> guix environment --ad-hoc --search-paths r-learnr  5,90s user 0,09s system 210% cpu 2,844 total
>>> $ time guix environment --ad-hoc  --search-paths r-learnr --no-grafts
>>> guix environment --ad-hoc --search-paths r-learnr --no-grafts  2,03s user 0,08s system 164% cpu 1,277 total
>>
>> I'm opening a new issue to track optimizing the grafting code, since
>> it's independent of environments (grafts are applied anytime a
>> derivation is built, AFAICT).  Grafting is inherently IO-bound,
>
> What is slow above is not grafting itself: it’s determining what to
> graft that takes CPU time.

On my system, grafting seems IO rather than CPU bound, I'm guessing
because of the need to scan all the files for strings to replace in the
graft process.

> I had reopened the initial bug at <https://issues.guix.gnu.org/41702>;
> should we close this one?

Many optimizations were made in the above issue that were not related to
the grafting process, so to me a fresh entry such as this one is clearer
to follow.  That said, feel free to proceed as you see fit, being the
issue "owner" :-).

Thanks,

Maxim