[bitbake-devel] Should multiconfig save build time?

Alan Kozlay alan.kozlay at ves-solutions.com
Wed Jul 10 15:58:35 UTC 2019

Thanks for the feedback.

On Wed, Jul 10, 2019 at 5:32 AM Richard Purdie <
richard.purdie at linuxfoundation.org> wrote:

> On Mon, 2019-07-08 at 14:27 -0400, Alan Kozlay wrote:
> > We're looking for things we can do to improve the multiconfig build
> > time.
> >
> > Even on our build servers it still takes a long time.
> > For instance, our build servers each have 64 core, 128G RAM with 4
> > NVMe SSD HDs in a striped raid (all configured with bells and
> > whistles to make it super fast).
> > A full fresh build on one of those servers still takes 6 hours.
> Given we have no idea what these mulitconfigs are, how much overlap
> there is or how you're running it, its hard to know whether 6 hours is
> good or bad.
> > I need to also clarify that we do indeed define different
> > DISTRO_FEATURES between multiconfigs, so multiconfig is necessary.
> >
> > (1) We're attempting to use the ccache (via ccache.bbclass), but it's
> > causing some build errors that we're investigating.
> That shouldn't cause errors and would likely be some ccache problem.
> > (2) Can we at least set the root native work directory to be the same
> > for all multiconfigs?
> It depends if the configurations are different or not. WORKDIR isn't
> your problem here, you really need the builds to have the same sysroot-
> components dir for the native case too, else this won't work. Its more
> about the output from the task than the directory they were built in.
> > Would each multiconfig honor the previously built native tools?
> > Or, would it just rebuild them, anyway?
> > Is this safe or tested or supported?
> multiconfig is configured so that if it sees overlapping stamp files it
> would handle that correctly. The tricky part is you'd have to split
> some directories which aren't usually split such as sysroot-components.
> I've never seen that attempted and am not sure if it would work or not.
> > (3) We're considering a network shared sstate-cache.  But it's not
> > entirely clear if a multiconfig build is benefited by the sstate-
> > cache directory.
> > Under what circumstances does a multiconfig leverage sstate-cache
> > when building for another multiconfig?
> Right now today for a single multiconfig build it won't.
> > What if the recipe would be affected by a change in DISTRO_FEATURES
> > between multiconfigs?
> > Are native packages included in the sstate-cache or just target
> > packages?
> native and target are included in sstate-cache.
> > We welcome all thoughts and ideas.
> With current bitbake you'd be best off splitting your multiconfig build
> into two parts a first stage where you build common shared components
> and a second where you leverage them.
> I appreciate that isn't a good solution but its what will work right
> now.
> The initial work in adapting bitbake to better handle situations like
> this is being done, as we speak and there are patches starting it in
> master-next.
> Right now those patches also won't change anything for you, they re-
> architect the codebase so we have a chance of implementing what you
> want. It is however at least a start. I'm working on this effectively
> alone with the day to day patch review, email and bugs to handle at the
> same time :(. As a project we know this is important but we struggle to
> find people willing to contribute development resources to make these
> kinds of changes happen.
> Next step is to write a regression test suite for runqueue. Once I've
> done that I'll start to think about optimisation work.
> Cheers,
> Richard

Alan Kozlay
VES Solutions, LLC
Alan Kozlay <alan.kozlay at ves.solutions>
DESK 443-595-7734
CELL 443-752-0323
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