Hi Sander
This does sound exciting! We (Codethink) would definitely be interested
in this for our CTRL OS solution, which in practice would mean starting
with freedesktop-sdk I think. Colleagues are digesting your proposal as
I write :)
br
Paul
On 2025-10-20 18:06, Sander Striker wrote:
Hi,
I’ve been working on a proposal that I’m really excited to share. It
could
significantly improve BuildStream’s performance on large dependency
graphs,
especially for C/C++ codebases, without changing correctness or
requiring
new semantics from build tools. This builds on top of the current
state of
the art, using both Remote Execution for parallelism and using recc to
cache and remote execute compilation at the translation unit level.
I've put the full proposal in issue #2083
<https://github.com/apache/buildstream/issues/2083>, as that renders
the
included diagrams nicely. I'll not rehash it here as it is quite long.
A
quick summary:
When we build an element, sub-actions are spawned, e.g. compile through
recc. We can record these subactions, and in a next build
speculatively
execute those same sub-actions, with updated files, at the start of the
build. We can do this aggressively for all actions regardless of what
element they correspond to in the dependency graph. When elements are
built, the sub-actions within will receive cache hits, dramatically
speeding up the overall end-to-end build.
I am quite happy with the limited amount of additional bookkeeping that
is
required to implement the proposal. I do think it is a step towards
Bazel's promise of "{ Fast, Correct } — Choose two", while not
requiring
all projects/elements to adopt a different build system.
I’d love to hear thoughts on
- the proposal in general
- the best way to integrate speculative action scheduling with
BuildStream’s element execution model
- any projects you'd like to try this on
I am looking for all the help I can get to prove this idea 😉; if you
have
an interest and some spare cycles to throw at this let me know. I'll
try
to make a start this week.
Cheers,
Sander
