[Buildroot] Use Pigz instead of gzip for filesystem compression

[Peter Korsgaard]

>>>>> "Vincent" == Vincent Fazio <vfazio at xes-inc.com> writes:

 > Louis-Paul,
 > On 3/6/20 10:43 AM, lpdev at cordier.org wrote:
 >> Hi all,
 >> 
 >> I have an improvement suggestion for filesystem compression. I have
 >> done some benchmark with pigz program (see https://zlib.net/pigz/).
 >> 
 >> Calling make after the target has been built the first time,
 >> buildroot has to compress a 850MB filesystem (build machine is
 >> i7-6700K CPU @ 4.00GHz):
 >> 
 >> gzip: 2m23s
 >> pigz: 46s
 >> 
 >> It's almost 3 times faster.
 >> 
 >> In the main Config.in, I suggest to add to Build options -> Command
 >> menu a BR2_GZIP command that would allow to specify the gzip program
 >> we want to use. Or better would be to set pigz as an host package.
 >> Then updating fs/common.mk:
 >> 
 >> ifeq ($$(BR2_TARGET_ROOTFS_$(2)_GZIP),y)
 >> ROOTFS_$(2)_COMPRESS_EXT = .gz
 >> ROOTFS_$(2)_COMPRESS_CMD = $(BR2_GZIP) -9 -c -n
 >> endif
 > If the commandline parameters are the same, this could likely be done
 > within support/dependencies/check-host-gzip.sh ?

We have to be careful to only use pigz where we are not interested in
bit-identical output (like we are for the tarballs of git repos). For
details, see:

commit 2218dc85bef9bb1c9d27788e5ac69593144fe268
Author: Yann E. MORIN <yann.morin.1998 at free.fr>
Date:   Sat Nov 17 18:15:51 2018 +0100

    support/dependencies: add a check for a suitable gzip

-- 
Bye, Peter Korsgaard