Hello Guix! Over the last few days I’ve been head-down working on ‘wip-build-systems-gexp’, the mythical branch that brings gexps to build systems and packages, so we can say goodbye to ‘build-expression->derivation’. And… it’s quite a ride!
I rebased it on ‘core-updates’, which was a bit tedious (it hadn’t been touched in 3 years or so). There are still test failures and build systems not yet converted, but that’s the easy part, although both are time-consuming. The more difficult part is performance. On current ‘core-updates’ I get: --8<---------------cut here---------------start------------->8--- $ GUIX_PROFILING=gc time ./pre-inst-env guix build qemu -d --no-grafts /gnu/store/z27l6plrxr5wm7818xhj9mdll99jcqz3-qemu-5.1.0.drv Garbage collection statistics: heap size: 80.52 MiB allocated: 191.14 MiB GC times: 15 time spent in GC: 0.66 seconds (32% of user time) 2.05user 0.12system 0:01.93elapsed 112%CPU (0avgtext+0avgdata 242872maxresident)k 0inputs+0outputs (0major+34228minor)pagefaults 0swaps --8<---------------cut here---------------end--------------->8--- but on ‘wip-build-systems-gexp’ I get: --8<---------------cut here---------------start------------->8--- $ 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 --8<---------------cut here---------------end--------------->8--- In short, 30% more garbage allocated and an 8% slowdown. 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. Statprof and gcprof are not super helpful here; I feel a need for better tools here, or better metrics. Anyway, that’s the situation. If you have ideas or if you’re in a profiling & optimization mood, now’s the time to unleash your creativity. :-) Ludo’.
