Re: [yocto] Parallel builds under yocto

[Mikko Rapeli <mikko.rapeli@linaro.org>]

Hi,

On Wed, Aug 14, 2024 at 09:36:05PM +0200, Alexander Kanavin via lists.yoctoproject.org wrote:
> Also there are sensible defaults for both, which use autodetection for
> how many cores a system cpu has. Generally you need to start tweaking
> these settings only when defaults aren't working well (e.g. if the
> system doesn't have enough RAM to support that many instances of gcc).

And when RAM becomes the limiting factor, one rule of thumb is to follow
CPU thread count until each thread has at least 2 Gb of physical RAM available.

On complex builds with lots of C++ (qt and friends) this seems to be a good
upper limit.

Less than 2 Gb per CPU thread results in OOM killer actions during building/linking
steps.

If one tracks builds CPU, memory, local disk and networking load with Performance Co-Pilot
or similar tools, it can be deduced that builds are CPU bound only some of the time
and a lot of time they are actually memory and local disk IO bound. Thus reducing
disk writes helps.

http://events17.linuxfoundation.org/sites/events/files/slides/elce-2016-mario-goulart-mikko-rapeli.pdf
and slides 49 and 50, for one setup.

Cheers,

-Mikko