[OE-core] [PATCH v2 2/4] bitbake.conf: more deterministic xz compression (threads)

[André Draszik]

xz archives can be non-deterministic / non-reproducible:
    a) archives are created differently in single- vs
       multi-threaded modes
    b) xz will scale down the compression level so as to
       be try to work within any memory limit given to
       it when operating in single-threaded mode

This means that due to bitbake's default of using as many
threads as there are cores in the system, files compressed
with xz will be different if built on a multi-core system
compared to single-core systems. They will also potentially
be different if built on single-core systems with different
amounts of physical memory, due to bitbake's default of
limiting xz's memory consumption.

Force multi-threaded operation by default, even on single-core
systems, so as to ensure archives are created in the same
way in all cases.

Signed-off-by: André Draszik <git at andred.net>
---
 meta/conf/bitbake.conf | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meta/conf/bitbake.conf b/meta/conf/bitbake.conf
index e201b671bb..131ba296d3 100644
--- a/meta/conf/bitbake.conf
+++ b/meta/conf/bitbake.conf
@@ -795,7 +795,7 @@ BB_NUMBER_THREADS ?= "${@oe.utils.cpu_count()}"
 PARALLEL_MAKE ?= "-j ${@oe.utils.cpu_count()}"
 
 # Default parallelism and resource usage for xz
-XZ_DEFAULTS ?= "--memlimit=50% --threads=${@oe.utils.cpu_count()}"
+XZ_DEFAULTS ?= "--memlimit=50% --threads=${@oe.utils.cpu_count(at_least=2)}"
 
 ##################################################################
 # Magic Cookie for SANITY CHECK
-- 
2.23.0.rc1