On Apr 4, 2019, at 1:59 AM, Ludovic Courtès <ludo@gnu.org> wrote:

The build nodes may be slower than the front-end, but still, it seems
unlikely that it would take more than 6h there.  (That could happen if
the test suite, which lasts 2.1h, were “embarrassingly parallel”, but
we’re running tests with ‘-j1’.)

To summarize, there are two problems:

 1. Rust takes too long to build.  What can we do about it?  Enable
    parallel builds?

Rust tests are designed to run in parallel, as long as you have enough
RAM, file descriptors, etc. available on the machine for the amount of
concurrency being used. The compiler test suite is largely just compiling
files, so the most important resource is probably available RAM/swap.

On Apr 4, 2019, at 2:28 AM, Pierre Langlois <pierre.langlois@gmx.com> wrote:

One thing I suggested in the past was to remove the check phase *only*
for rust packages used for bootstrapping. This way we still run the
tests for the final rust but not at every step in the chain.

Although, I wonder if we're more likely to miss a bug if we do this, I'm
not sure.

Although that definitely will speed the bootstrap chain, I’m concerned that
if a dependency package ever gets updated and breaks things we wouldn’t
know without running the test suite.

Maybe if the bootstrapped versions don’t ever change skipping the check
phase will be safe, but I think we should try running parallel tests first
and see how far that gets us.