substitute: Choose compression method based on past CPU usage.

This stems from the observation that substitute download can be
CPU-bound when high-speed networks are in use:

  https://lists.gnu.org/archive/html/guix-devel/2020-12/msg00177.html

* guix/narinfo.scm (decompresses-faster?): New procedure.
(narinfo-best-uri): Add #:fast-decompression?.
* guix/scripts/substitute.scm (%prefer-fast-decompression?): New
variable.
(call-with-cpu-usage-monitoring): New procedure.
(with-cpu-usage-monitoring): New macro.
(display-narinfo-data, process-substitution): Pass #:fast-decompression?
to 'narinfo-best-uri'.
(process-substitution): Wrap 'restore-file' call in
'with-cpu-usage-monitoring'.  Set '%prefer-fast-decompression?'.

0 files changed, 0 insertions, 0 deletions