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

[R0b0t1 <r030t1@gmail.com>]

Hello,

On Wed, Nov 22, 2017 at 12:52 AM, Raffaele Belardi
<raffaele.belardi@st.com> wrote:
> Hi,
>
> 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. 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.
>

Assuming all of your compilation is on a RAM disk, there are two main
bottlenecks that are easy to spot: network access (downloading new
packages) and dependency chokepoints (packages must be compiled in a
chain). Other potential chokepoints like disk access are negligible in
my experience, though for one merge I did have two or three ebuilds
fighting for disk IO "lock up" a system.

If all dependencies have been satisfied on your system I invite you to
merge a bunch of packages at once (@world?), you should notice greater
parallelism.

> Does anyone have real-world statistics of CPU usage based on gentoo world build?
>

I've considered ways to gather these statistics off and on over the
years, but it is easy to start sinking a lot of time into it. It is
possible the data you want exists, but I have not found any extant
solution involving portage that provides that detail of logging.*

Cheers,
     R0b0t1


* Someone will prove me wrong in 3... 2... 1...