[tor-dev] Making Tor's CI Faster

[teor]

Hi,

Want to help make Tor's CI go faster?

As part of the Sponsor 55 IPv6 work, I need to run Chutney IPv6 tests
on every Tor commit, as part of Tor's CI.

We're currently running these tests with fast_finish, because:
* Travis CI only has IPv6 on macOS
* macOS Chutney tests take 20-45 minutes in Travis CI
But fast_finish requires allow_failure.

We can't have allow_failure on code that's we're modifying every day,
so I'm going to make the Travis IPv6 Chutney job mandatory.

To speed up CI after this change, I'm going to make a new IPv6-only
test-network target, and run it in the macOS CI:
https://trac.torproject.org/projects/tor/ticket/33280

I've also identified one redundant Travis CI job that we can delete:
https://trac.torproject.org/projects/tor/ticket/33195#comment:3

Overall, these changes should reduce total CI runtime by 20-35
minutes. Due to parallelism, the wall clock time should reduce by
10-35 minutes. We can squeeze the most benefit from the parallelism
by sorting jobs in speed order (longest first):
https://trac.torproject.org/projects/tor/ticket/33194

If you have any other ideas for making Tor's CI go faster, please let
me know.

Slow CI is a particular issue for backports, because each 0.3.5
backport updates 9 branches:
  * {maint,release}-{0.3.5,0.4.1,0.4.2,0.4.3} and
  * master.

T

--
teor
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