speed up skipped build processing

[Mic92]

No description provided.

[MagicRB]

Shouldnt workers be able to attach to multiple builds?

[Mic92]

I don't think so. Before I added one worker per CPU, it would only process one build at the time.

[MagicRB]

Then what's that?
Concurrencu must be blocked by locks.
Right do we have a lock in the skipped build builder?

[Mic92]

I checked now a couple of times and with this change the time reduces from 20s to 15s for "skipping" disko

[zowoq]

I tried this branch on a fully cached nixvim eval a few days ago. There wasn't any other buildbot/hydra jobs running at the time.

With this branch: 1:06 https://buildbot.nix-community.org/#/builders/26/builds/20

Without: 28:23 https://buildbot.nix-community.org/#/builders/26/builds/21

I ran another one without today: 38:14 https://buildbot.nix-community.org/#/builders/26/builds/95

[Mic92]

That's quite significant. Before I had skipped builds not actually having to run any code i.e. build steps. I think they were faster back than. I wish there was a better way to insert a build without any involvement of the scheduler.

[MagicRB]

While this works, I don't like that we don't know why the worker won't accept more than one build at a time. I'll try to debug that.

[MagicRB]

buildbot/buildbot#7125 okay this is this, it was not obvious from the code, but yeah, its one builder one worker so it won't run multiple. We should do the same for the NixEval builder then