Rust packages and performance impact on Guix

[Ludovic Courtès]

Hi!

Ludovic Courtès <ludo@gnu.org> skribis:

> but on ‘wip-build-systems-gexp’ I get:
>
> $ GUIX_PROFILING=gc time ./pre-inst-env guix build qemu -d --no-grafts
> /gnu/store/5n44l8cmrmkr747nsqbxpm4764jdsl3l-qemu-5.1.0.drv
> Garbage collection statistics:
>   heap size:        80.52 MiB
>   allocated:        249.89 MiB
>   GC times:         16
>   time spent in GC: 0.75 seconds (34% of user time)
> 2.22user 0.13system 0:02.06elapsed 114%CPU (0avgtext+0avgdata 
> 243532maxresident)k
> 0inputs+0outputs (0major+34304minor)pagefaults 0swaps
>
> In short, 30% more garbage allocated and an 8% slowdown.

In the meantime, librsvg on core-updates switched to the version that
depends on Rust.  As a result, the above command, on core-updates, went
to ~2.25s on my laptop (+10–20%!).

Would be nice to investigate.  One issue is that ‘cargo-build-system’
traverses packages.  The ‘crate-closure’ call in there certainly adds a
fair bit of overhead.  Could we avoid it?

Thanks,
Ludo’.