bug#32548: Cuirass: Performance monitoring

[Mathieu Othacehe]

Hello,

> As discussed earlier today on IRC with Clément, we could add performance
> monitoring capabilities to Cuirass.  Interesting metrics would be:
>
>   • time of push to time of evaluation completion;
>
>   • time of evaluation completion to time of build completion.

Small update on that one. With Cuirass commit
154232bc767d002f69aa6bb1cdddfd108b98584b, we now have the following
timestamps:

* Checkout commit time.
* Evaluation creation.
* Evaluation checkouts completion.
* Evaluation completion.

For the first timestamp, I'm using Guile-Git to extract the commit time,
which is not the commit push time. In fact, I think there is no such
thing as "commit push time" in git.

We can still compute the metric 'time of commit to time of evaluation
completion', but it's less relevant than the proposed 'time of push to
time of evaluation completion'.

The other proposed metric, 'time of evaluation completion to time of
build completion' can now be computed.

Regarding the actual computation and reporting of those metrics, I'm
still considering different options. I'd like to have a look to
Guile-prometheus that is written by Christopher.

Thanks,

Mathieu