packages, scripts, utils: Enable multi-threaded xz compression.

xz compression is slow; using the multi-thread mode of xz can make it more
than 6 times faster, for example when compressing the large linux-libre
source.

* guix/build/utils.scm (%xz-parallel-args): New procedure.
* guix/packages.scm (patch-and-repack): Specify the required above xz
arguments by setting the XZ_DEFAULTS environment variable.
* guix/scripts/pack.scm (%compressors, bootstrap-xz): Modify the commands
Gexps so they do not need to be quoted.  This allows lazily evaluating the
arguments on the builder's side.  Specify the required xz arguments.
(self-contained-tarball): Do not quote the compressor command value.
(docker-image): Likewise.
* guix/utils.scm (decompressed-port, compressed-port)
(compressed-output-port): Specify the required above xz arguments.

1 files changed, 14 insertions, 1 deletions

diff --git a/guix/build/utils.scm b/guix/build/utils.scm
index 533b740896..fe2d82c99e 100644
--- a/guix/build/utils.scm
+++ b/guix/build/utils.scm
@@ -113,7 +113,9 @@
 
             make-desktop-entry-file
 
-            locale-category->string))
+            locale-category->string
+
+            %xz-parallel-args))
 
 
 ;;;
@@ -1484,6 +1486,17 @@ returned."
              LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONE
              LC_TIME)))
 
+
+;;;
+;;; Others.
+;;;
+
+(define (%xz-parallel-args)
+  "The xz arguments required to enable bit-reproducible, multi-threaded
+compression."
+  (list "--memlimit=50%"
+        (format #f "--threads=~a" (max 2 (parallel-job-count)))))
+
 ;;; Local Variables:
 ;;; eval: (put 'call-with-output-file/atomic 'scheme-indent-function 1)
 ;;; eval: (put 'call-with-ascii-input-file 'scheme-indent-function 1)