Efraim Flashner wrote:
> * guix/scripts/pack.scm (%compressors): Add flag '-T0' when calling "xz".
> * guix/utils.scm (decompressed-port, compressed-port,
> compressed-output-port): Same.

> --- a/guix/utils.scm
> +++ b/guix/utils.scm
> @@ -154,7 +155,7 @@ a symbol such as 'xz."
>    (match compression
>      ((or #f 'none) (values input '()))
>      ('bzip2        (filtered-port `(,%bzip2 "-dc") input))
> -    ('xz           (filtered-port `(,%xz "-dc") input))
> +    ('xz           (filtered-port `(,%xz "-dc -T0") input))
>      ('gzip         (filtered-port `(,%gzip "-dc") input))
>      (else          (error "unsupported compression scheme" compression))))

Parallel decompression isn't implemented yet, but the extra '-T0' option
doesn't seem to break anything.

The changes LGTM.

I sent a companion patch to <https://bugs.gnu.org/26316> that enables
threaded compression when building source tarballs.