Re: -CURRENT compilation time

On Mon, 6 Sept 2021 at 11:44, David Chisnall <theraven@freebsd.org> wrote:
>
> On 06/09/2021 09:08, Jeremie Le Hen wrote:
> > 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).
>
> Note that you need to build LLVM twice only if you are actively
> debugging LLVM reproduceable deployment images.  You actually don't need
> to build it at all, you can use an external toolchain to skip the first
> build and you can compile WITHOUT_TOOLCHAIN  to avoid building the
> version that's installed and then install a toolchain from packages:
>
> https://wiki.freebsd.org/ExternalToolchain

I did a test on a 16 core (32 VCPU) machine (Intel(R) Xeon(R) CPU
E5-2630 v3 @ 2.40GHz).

With the option WITHOUT_TOOLCHAIN=yes the world build time is 2.5
times faster (real or user+sys), down from 48 min to 19.5 min real
time.

time make -j16 buildworld
--------------------------------------------------------------
>>> World build completed on Mon Sep  6 12:00:45 UTC 2021
>>> World built in 2862 seconds, ncpu: 32, make -j16
--------------------------------------------------------------
     2862.04 real     41234.87 user      1582.66 sys

time make -j16 WITHOUT_TOOLCHAIN=yes buildworld
--------------------------------------------------------------
>>> World build completed on Mon Sep  6 11:32:41 UTC 2021
>>> World built in 1181 seconds, ncpu: 32, make -j16
--------------------------------------------------------------
     1180.73 real     16076.27 user       988.73 sys

-Wolfram

-- 
Wolfram Schneider <wosch@FreeBSD.org> https://wolfram.schneider.org