On 31 août 2015, at 20:41, Tim Graham <timogra...@gmail.com> wrote:

> Aymeric, did you envision any changes to Django's CI setup?

Glad you asked :-) I have some thoughts but no definitive opinion.

> Currently we run 1 Jenkins executor per CPU, so I don't know that adding 
> parallelization would have any benefit? (We are already using all 8 CPUs when 
> we're running 8 concurrent builds from the matrix.)  

Indeed, we’re already parallelizing by running simultaneously tests against 
multiple databases. So we aren’t going to make order-of-magnitude gains.

The last processes of a given build may complete a bit faster if they’re run in 
parallel mode as they will make better use of the server’s resources once there 
are fewer active executors than CPUs. So the completion time for a matrix build 
may be slightly lower, unless the increased concurrency slows tests down 
sufficiently to negate this effect.

If increased concurrency is a problem, half the number of executors running 
tests with --parallel-num=2 should still complete faster, because it “packs” 
CPU usage more efficiently towards the end of the matrix build. It’s hard to 
tell what’s going to happen without trying.

> If not, then I wonder how we can ensure that Django's test suite continues to 
> work well in parallel.

Perhaps we could make the --parallel option the default in runtests.py. You’d 
have to pass --parallel-num=1 to disable it. This would help occasional 
sprinters unfamiliar with the option. They could just run ./runtests.py, melt 
their laptops, and not even have time for a coffee break.

-- 
Aymeric.




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