On Thu, Mar 30, 2017 at 06:17:15PM -0400, Leo Famulari wrote:
> This patch enables multi-threaded xz compression in the repacking stage
> of building source tarballs.
> 
> With it applied, I get a ~2.2x speedup building the source of
> linux-libre with 4 threads, compared to 1 thread.
> 
> Specifically, with the upstream linux-libre tarball in the page cache,
> `guix build -S linux-libre` took ~366 seconds using a single thread for
> xz, and ~164 seconds using 4 threads.

> From 78547a09e50440c649c3d28d7691f32fdd47cc25 Mon Sep 17 00:00:00 2001
> From: Leo Famulari <leo@famulari.name>
> Date: Thu, 30 Mar 2017 03:10:48 -0400
> Subject: [PATCH] packages: Enable threaded compression of source tarballs.
> 
> This provides a ~2x speedup when using 4 threads.
> 
> * guix/packages.scm (patch-and-repack)[build]: Invoke xz with
> '--threads=0' when re-packing tarballs.

I pushed this to core-updates as
c8a3dea847bb9f87fa1876d0c6c3356d6226f121.