Re: [gentoo-user] is multi-core really worth it?

[J. Roeleveld]

On Wednesday, November 22, 2017 8:48:08 AM CET David Haller wrote:
> Hello,
>
> On Wed, 22 Nov 2017, Raffaele Belardi wrote:
> >rebuilding system and world with gcc-7.2.0 on a 6-core AMD CPU I have
> >the impression that most of the ebuilds limit parallel builds to 1, 2
> >or 3 threads.
>
> Most should build with "many" cores, but some might be limited, but ...
>
> >I'm aware it is only an impression, I did not spend the
> >night monitoring the process, but nevertheless every time I checked
> >the load was very low.
>
> I guess you're mostly observing stalls because the (single-thread)
> overhead of emerge, configure (etc.), which can also be IO-bound...
> The actual builds probably goes so fast on your box, you hardly
> notice unless they're rather big(gish).
>
> Some numbers for comparison, and I generally build with just one
> thread in the background on my 2 core "old" Athlon II X2 250:
> dev-libs/boost took a good 45mins to build with one thread. Divide by
> 6 for your cores, divide again by about 2-3 for your newer cores and
> you're in the 3:45min range for such a "biggie" as boost. Most other
> stuff won't even peg your meter.
>
> So, your emerge is mostly IO and "emerge"-threads bound. Solution:
> adjust your build-threads[1], and then adjust your emerge jobs! See
> '--jobs' in 'man emerge'. Can't find where to set a default in a
> config-file for that ATM, but you could always alias/function/script
> emerge to something else, e.g. put this in your ~/.bashrc:

Instead of all these aliases, simply edit your make.conf ( /etc/portage/
make.conf )

And edit (or add) the following lines:
MAKEOPTS="--jobs 24 --load-average 48"
EMERGE_DEFAULT_OPTS="--jobs 24 --load-average 48"

Adjust the values to match your system, the above works fine on my desktop.
CPU: Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz
And 32GB ram.

--
Joost