Re: ci: reduce macos test concurrency

Hi,

On 2022-09-26 21:02:08 -0700, Andres Freund wrote:
> The x86 mac VMs from cirrus-ci claim to have 12 CPUs, but when working on
> initdb caching for tests I noticed that using all those CPUs for tests hurts
> the test times noticably.
>
> See [1] (note that the overall time is influenced by different degrees of
> cache hit ratios):
>
> concurrency test time:
> 4 05:58
> 6 05:09
> 8 04:58
> 10 05:58
> 12 (current) 06:58
>
> There's a fair bit of run-to-run variance, but the rough shape of these
> looks repeatable.
>
> I suspect the VMs might be overcommitted a fair bit - or macos just scales
> poorly. Cirrus-ci apparently is switching to M1 based macs, which could be
> related. It'd be good for us do that switch, as it'd give use ARM coverage for
> CI / cfbot. See also [3].
>
>
> In 15 (and thus autoconf) the timings differ a bit less [2]:
>
> concurrency test time:
> 4 06:54
> 6 05:43
> 8 06:09
> 10 06:01
> 12 (current) 06:38
>
> Looks like changing TEST_JOBS=6 or 8 would be a good idea.

Set it to 8 now.

Greetings,

Andres Freund