bug#47137: [PATCH] Adaptive substitute decompression selection

[Ludovic Courtès]

Hi!

Ludovic Courtès <ludo@gnu.org> skribis:

> The patch below is a followup to the thread started in December:
>
>   https://lists.gnu.org/archive/html/guix-devel/2020-12/msg00177.html
>
> It provides a naïve but apparently good enough way for ‘guix substitute’
> to choose the compression method that yields the best speed given the
> CPU and current networking conditions.
>
> On a recent x86_64 laptop with fast networking, using ci.guix.gnu.org,
> the effect so far is to choose gzip substitutes, which indeed provides
> slightly faster substitute installation.  When ci.guix provides zstd
> substitutes, the speedup will be higher.
>
> I have yet to check that it sticks to lzip when bandwidth is low.

I did that, using ‘tc’, and it works as expected, staying on lzip.

Pushed as 9da5ec7099b992a8969a17627548cd341c01bd90 with two minor
tweaks: lowered the low hysteresis threshold, and added a comment on how
to use ‘tc’ to test the behavior on “slow” networks.

Rather than running ‘guix build’ followed by ‘guix gc’, I found that
manually invoking ‘guix substitute’ was nicer (long line ahead!):

  ( echo substitute /gnu/store/svv4826f8zfj8grl2qa17xnxk3acsppc-elixir-1.11.4 
/tmp/t1; echo substitute 
/gnu/store/d9dk53m7pwx1dc1p97zm0q323gpk70f9-poezio-0.13.1 /tmp/t4; echo 
substitute /gnu/store/mra8i18y9gjavhmdlkbb10m4miinirgz-ocaml-4.11.1 /tmp/t2; 
echo substitute /gnu/store/ay2j5mp20j9vbhibcwp5lmmcmhqkdnga-vim-full-8.2.2632 
/tmp/t3; echo substitute 
/gnu/store/svv4826f8zfj8grl2qa17xnxk3acsppc-elixir-1.11.4 /tmp/t5; echo 
substitute /gnu/store/ay2j5mp20j9vbhibcwp5lmmcmhqkdnga-vim-full-8.2.2632 
/tmp/t6) | GUIX_ALLOW_UNAUTHENTICATED_SUBSTITUTES=yes ./pre-inst-env guix 
substitute --substitute 4>&2

Note that this change won’t take effect until we update the ‘guix’
package.

Ludo’.