Re: [Qemu-devel] [PATCH] build: change dist target to use xz

[Eric Blake <eblake@redhat.com>]

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On 01/04/2013 05:28 PM, Brad Smith wrote:
> On Thu, Aug 02, 2012 at 06:08:15AM -0400, Brad Smith wrote:
>> If a compression format other than gzip is used we might
>> as well move to xz instead of bzip2.

Agreed, many projects are dropping bzip2 as irrelevant (slower than the
more-widely-available gz, compresses worse than newcomer xz).

> +++ b/scripts/make-release
> @@ -20,5 +20,5 @@ git checkout "v${version}"
>  git submodule update --init
>  rm -rf .git roms/*/.git
>  popd
> -tar cfj ${destination}.tar.bz2 ${destination}
> +XZ_OPT=-9 tar cfJ ${destination}.tar.xz ${destination}

Do we really need -9?  For example, coreutils did an interesting
benchmark in its cfg.mk file, and chose to use -8e instead of -9 as a
result:

>> # Comparing tarball sizes compressed using different xz presets, we see that
>> # an -8e-compressed tarball is only 9KiB larger than the -9e-compressed one.
>> # Using -8e is preferred, since that lets the decompression process use half
>> # the memory (32MiB rather than 64MiB).
>> # $ for i in {7,8,9}{e,}; do \
>> #     (n=$(xz -$i < coreutils-8.15*.tar|wc -c);echo $n $i) & done |sort -nr
>> # 5129388 7
>> # 5036524 7e
>> # 5017476 8
>> # 5010604 9
>> # 4923016 8e
>> # 4914152 9e

Also, your use of tar cfJ assumes relatively new GNU tar; it won't work
on other systems (but this is a pre-existing non-portability, and may be
irrelevant, if you are willing to require that the only people likely to
make a release tarball are using appropriate tools).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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