On Mon, 6 Sept 2021 at 10:10, Jeremie Le Hen <j...@freebsd.org> wrote:
>
> Hey,
>
> I want to build -CURRENT again from sources. It's been a long time
> since I hadn't done that. I'm shocked by the compilation time.
>
> I started the whole thing on Friday night and Monday morning it's
> still in stage 4.2 (building libraries). Through occasional glancing
> at the screen over the weekend, it seems obvious to me that the
> compilation time is utterly dominated by LLVM. Compiling C++ seems
> extremely CPU heavy and this is made worse by the fact LLVM is built
> twice (once for build/cross tools, once for the actual world).
>
> So OK, my CPU is not the most powerful out there but it's still decent [1].
>
> So I have a couple of questions coming to my mind:
> 1. Is there any optimization I could benefit from? (I'm sure there's a
> knob to use the existing compiler instead of building a
> cross-compiler.)
> 2. More generally, isn't this compilation time not considered as a
> problem for developers? This seems to terribly slow down the iteration
> time for people working on the build system. I wouldn't be surprised
> if this drove people away from working on/improving that area.
>
> [1]
> https://www.cpubenchmark.net/cpu.php?cpu=Intel+Core+i5-6260U+%40+1.80GHz&id=2671
Hi,
I ran buildworld yesterday on a 3 CPU VM (AMD EPYC 2.4GHz) and the
runtime was 2h. We spent most of the time in "stage 4.2: building
libraries", in my case 62% of the CPU time and 75% of the real time.
I guess the build time on your laptop should be around 6 hours if
everything is ok.
time make -j $(sysctl -n hw.ncpu) buildworld > log.buildworld 2>&1
tail -n 5 log.buildworld
--------------------------------------------------------------
>>> World build completed on Sat Sep 4 20:58:00 UTC 2021
>>> World built in 7235 seconds, ncpu: 3, make -j3
--------------------------------------------------------------
7235.61 real 20527.30 user 915.88 sys
egrep '>>> stage| real ' log.buildworld
>>> stage 1.1: legacy release compatibility shims
0.28 real 0.18 user 0.10 sys
>>> stage 1.2: bootstrap tools
165.99 real 472.58 user 11.56 sys
>>> stage 2.1: cleaning up the object tree
21.47 real 36.96 user 14.14 sys
15.87 real 29.14 user 11.87 sys
>>> stage 2.3: build tools
2.42 real 3.79 user 0.62 sys
>>> stage 3: cross tools
9.92 real 18.49 user 1.75 sys
>>> stage 3.1: recording build metadata
0.07 real 0.01 user 0.06 sys
>>> stage 4.1: building includes
16.62 real 36.46 user 9.48 sys
>>> stage 4.2: building libraries
5440.89 real 15724.60 user 482.58 sys
>>> stage 4.3: building lib32 shim libraries
615.91 real 1654.77 user 164.58 sys
>>> stage 4.4: building everything
937.23 real 2540.06 user 205.47 sys
-Wolfram
--
Wolfram Schneider <wo...@freebsd.org> https://wolfram.schneider.org
