Re: [BuildStream] Switching to buildbox-run for local builds

[Jürg Billeter <j bitron ch>]

Hi Chandan,

On Mon, 2020-04-27 at 20:58 +0100, Chandan Singh wrote:
> Hi Jürg,
>
> Thanks for the write up, and more importantly for your efforts towards
> making buildbox-run work nicely.
>
> Definitely +1 from my side.
>
> One question comes to mind - have you observed any differences in
> performance using the buildbox backend compared to the bwrap one?

In my test builds of freedesktop-sdk I've noticed virtually no
difference in build time (144 min with bwrap vs. 142 min with buildbox-
run-bubblewrap+fuse). However, that build time is obviously dominated
by actual build commands. I haven't done any microbenchmarks of the
BuildStream/BuildBox overhead yet.

The difference may vary depending on the project. E.g., staging and
integration commands are much faster with buildbox-fuse (no hardlinking
and buildbox-fuse is much more efficient than pyfuse) while filesystem
access by build commands is slightly slower with buildbox-fuse (context
switch for not yet cached directory entries).

I haven't benchmarked BuildStream with buildbox-run with hardlinking
(i.e., without buildbox-fuse) yet. My focus has been on buildbox-run-
bubblewrap+fuse as that's the direct replacement of the current bwrap
(+pyfuse) backend, which is also Linux-only.

I expect the overall performance with buildbox-fuse to improve with
future optimizations, e.g., it should be relatively easy to optimize
output capturing.

> I'd be in favor of keeping the bwrap backend around for a little
> while. This is mostly to allow for a smoother fallback in case there
> are any issues, and for performance comparisons. I understand that one
> could fall back to an older version, but it'll be slightly nicer to be
> able to compare master branches in both cases. This is not a big issue
> but given that it doesn't cost us much to keep it for a while, I'd be
> in favor of that.
>
> Time-wise, maybe we can give it a month or so?

Sure, we can keep it around for a bit. I will also add a CI job to keep
testing bwrap until we remove the code, of course.

Cheers,
Jürg