Building Kernel and World with -j

[Steven Hartland]

On 23/01/2017 07:24, Sergei Akhmatdinov wrote:
> On Sun, 22 Jan 2017 22:57:46 -0800
> Walter Parker <walterp at gmail.com> wrote:
>> For decades there has always been a warning not to do parallel builds of
>> the kernel or the world (Linux kernel builds also suggest not to do this).
>>
>> Every once in a while, I see people post about 5 minutes. This only way I
>> can see this happening is by doing a parallel build (-j 16 on a Xeon
>> Monster box).
>>
>> Are parallel builds safe? If not, what are actual risk factors and can they
>> be mitigated?
> Not only do I use -j, I also use ccache.
>
> Another option is to use WITH_META_MODE=YES, that's where most of the 5-minute
> reports come from, I imagine. I haven't used it myself.
>
> My kernel takes 10 minutes with world taking about two hours. I generally just
> leave them building overnight.
>
> The risks of parallel builds are mostly in the past, concurrency was still just
> coming out and there were chances that something would get compiled before it's
> dependency, breaking your compile and wasting all of those hours.
>
> Cheers,
We always use -j for both kernel and world for years.

While there's been a few niggles if the clock is out and its a rebuild 
they have been few and far between.

Current cut down kernel build time is 1m and world build time is 22m 
here for FreeBSD 11.0-RELEASE on a dual E5-2640.

     Regards
     Steve