[bug#67238] [PATCH] derivations: Avoid readlink syscalls in read-derivation-from-file.

["Ludovic Courtès" <ludo@gnu.org>]

Hi,

Christopher Baines <mail@cbaines.net> skribis:

> strace -c reports over 10,000 readlink syscalls when reading the derivation
> for the hello package. By just setting the %file-port-name-canonicalization
> fluid, this drops to less than 10.
>
> I'm not sure if this actually improves performance, but doing less is surely
> better.
>
> * guix/derivations.scm (read-derivation-from-file): Set
> %file-port-name-canonicalization to 'none when calling call-with-input-file.
>
> Change-Id: I1ff16a059160576a576f2e9ed881379596e66af3

[...]

> +      (let ((drv
> +             ;; Avoid calling scm_i_relativize_path in
> +             ;; fport_canonicalize_filename since this leads to lots of
> +             ;; readlink calls
> +             (with-fluids ((%file-port-name-canonicalization 'none))
> +               (call-with-input-file file read-derivation))))

This is already done in ‘run-guix’ in (guix ui), for all the ‘guix’
commands (so this patch would be a slight performance regression for
Guix itself).

I’d suggest setting this fluid globally in applications that use Guix
(the Build Coordinator, etc.), as is done in Guix itself.

WDYT?

Ludo’.