bug#61646: Bandwidth-induced offload timeout abort whole operating

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi Guix,

I can reproduce this rather easily on my system:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix build icedove
The following derivations will be built:
  /gnu/store/l6r93asndd0kwv7024iyrl71zd0lbpbq-icedove-102.7.2.drv
  /gnu/store/8zi808086b3vlfjrhdm87fgljziwdqx2-icedove-l10n-102.7.2.drv
  /gnu/store/v0sq7rb8fk36kjasb27a71z1a27wxb1s-icedove-minimal-102.7.2.drv
process 19542 acquired build slot '/var/guix/offload/localhost:6666/0'
normalized load on machine 'localhost' is 0.08
building /gnu/store/8zi808086b3vlfjrhdm87fgljziwdqx2-icedove-l10n-102.7.2.drv...
process 19548 acquired build slot '/var/guix/offload/localhost:6666/1'
normalized load on machine 'localhost' is 0.08
building /gnu/store/v0sq7rb8fk36kjasb27a71z1a27wxb1s-icedove-minimal-102.7.2.drv...
guix offload: sending 1 store item (558 MiB) to 'localhost'...
exporting path `/gnu/store/bwb5hcdyzgq16kmbsva7ax0zq6lzg78z-icedove-102.7.2.tar.xz'
guix offload: error: failed to connect to 'localhost': Timeout connecting to localhost
cannot build derivation `/gnu/store/l6r93asndd0kwv7024iyrl71zd0lbpbq-icedove-102.7.2.drv': 1 dependencies couldn't be built
guix build: error: build of
  `/gnu/store/l6r93asndd0kwv7024iyrl71zd0lbpbq-icedove-102.7.2.drv' failed
--8<---------------cut here---------------end--------------->8---

The third derivation tries to get a build slot and times out, because
the first two have already saturated the bandwidth of the link and it
takes more time than expected to get a reply.

The workaround is to use '-k', for "--keep-continuing", and retry the
3rd failing derivation after the first two completed.

I don't have a clear idea on how to improve the situation other than use
longer timeouts... but perhaps these timeouts could be dynamic based on
the load of the network/CPU/ ?

-- 
Thanks,
Maxim