Re: Will 2021 be the year of build systems on gexps?

["Ludovic Courtès" <ludo@gnu.org>]

Hi!

Ludovic Courtès <ludo@gnu.org> skribis:

> I’ve made progress identifying and mitigating what seems to be the main
> cause of this (the fact that it’s possible to ungexp a list and that
> list will be scanned in its entirety in search of file-like
> objects—convenient but expensive) but as you can see, there’s still a
> lot to do.

I cherry-picked to ‘master’ the gexp optimizations I made on
‘wip-build-systems-gexp’.  The good news is that it pays off on system
compilations, going from (commit 3c548c3e0eade12d3e86b1201dbd95863ca64ea7):

--8<---------------cut here---------------start------------->8---
$ GUIX_PROFILING="gc object-cache" ./pre-inst-env guix system build -d --no-grafts gnu/system/examples/desktop.tmpl
/gnu/store/g6kd2blajq6yja80516m85zv07d4ysb3-system.drv
Store object cache:
  fresh caches:     2
  lookups:      119282
  hits:         116225 (97.4%)
Garbage collection statistics:
  heap size:        119.43 MiB
  allocated:        649.07 MiB
  GC times:         26
  time spent in GC: 2.15 seconds (37% of user time)
--8<---------------cut here---------------end--------------->8---

to (commit 0a912b3a434c9ff9515f9036feae4d3a7075fb2f):

--8<---------------cut here---------------start------------->8---
$ GUIX_PROFILING="gc object-cache" ./pre-inst-env guix system build -d --no-grafts gnu/system/examples/desktop.tmpl
/gnu/store/f63c8rk8rwrfr5cl4s74hnx25l3z1hrp-system.drv
Store object cache:
  fresh caches:     2
  lookups:      119285
  hits:         116227 (97.4%)
  cache size:    3058 entries
Garbage collection statistics:
  heap size:        111.43 MiB
  allocated:        608.01 MiB
  GC times:         25
  time spent in GC: 2.00 seconds (37% of user time)
--8<---------------cut here---------------end--------------->8---

Reduced heap allocations (-6%), reduce heap size (-7%), and reduced run
time (ditto).  Getting better!

Ludo’.