Cuirass upgrade on ci.guix

[Ludovic Courtès]

Hello Guix!

A few hours ago I deployed current Cuirass on ci.guix and its build
machines.  The expected benefits are:

  1. Better throughput.  I fixed a bug that would lead “workers” to
     eventually get ignored by ‘cuirass remote-server’, meaning they
     would become idle until either the server or the worker is
     restarted¹.

     When I reconfigured, there were 45k pending builds (!), visible on
     <https://ci.guix.gnu.org/metrics> and the vast majority of workers
     at <https://ci.guix.gnu.org/workers> were idle.

     We’re now at ~22k pending builds (okay, I cheated by canceling ~15k
     from ‘emacs-team’, but I also restarted many builds en masse),
     which are mostly non-x86.

     My hope is that we can get close to zero soon and have headroom for
     feature branches.

  2. Evaluation can be triggered via POST requests, which should make
     things a bit more reactive and will allow us to poll repos less
     frequently.  I submitted a support request on Savannah:
     <https://savannah.nongnu.org/support/?110939>.

  3. Improved resilience against “evaluation storms” since ‘cuirass
     register’ now has an upper limit on the number of evaluations that
     may occur in parallel.

  4. Build priority handling has been restored (it had been lost
     recently).

As a bonus, we may finally get native GNU/Hurd builds again, via the
childhurds running on some of the build nodes.

That’s it!

Ludo’.

¹ 
https://git.savannah.gnu.org/cgit/guix/guix-cuirass.git/commit/?id=40f70d28aed55c404cca6a0760860fb4942e6bee