[PATCH] Adaptive substitute decompression selection

Hi!

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.

Thoughts?

Thanks,

Ludo’.

Hi!

Ludovic Courtès <ludo@gnu.org> skribis:

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’.