Re: [PATCH v4 4/5] qcow2: add zstd cluster compression

[Markus Armbruster <armbru@redhat.com>]

Denis Plotnikov <dplotnikov@virtuozzo.com> writes:

> zstd significantly reduces cluster compression time.
> It provides better compression performance maintaining
> the same level of the compression ratio in comparison with
> zlib, which, at the moment, is the only compression
> method available.
>
> The performance test results:
> Test compresses and decompresses qemu qcow2 image with just
> installed rhel-7.6 guest.
> Image cluster size: 64K. Image on disk size: 2.2G
>
> The test was conducted with brd disk to reduce the influence
> of disk subsystem to the test results.
> The results is given in seconds.
>
> compress cmd:
>   time ./qemu-img convert -O qcow2 -c -o compression_type=[zlib|zstd]
>                   src.img [zlib|zstd]_compressed.img
> decompress cmd
>   time ./qemu-img convert -O qcow2
>                   [zlib|zstd]_compressed.img uncompressed.img
>
>            compression               decompression
>          zlib       zstd           zlib         zstd
> ------------------------------------------------------------
> real     65.5       16.3 (-75 %)    1.9          1.6 (-16 %)
> user     65.0       15.8            5.3          2.5
> sys       3.3        0.2            2.0          2.0
>
> Both ZLIB and ZSTD gave the same compression ratio: 1.57
> compressed image size in both cases: 1.4G
>
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
[...]
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index a67eb8bff4..84889fb741 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -4401,11 +4401,12 @@
>  # Compression type used in qcow2 image file
>  #
>  # @zlib:  zlib compression, see <http://zlib.net/>
> +# @zstd:  zstd compression, see <http://github.com/facebook/zstd>
>  #
>  # Since: 5.0
>  ##
>  { 'enum': 'Qcow2CompressionType',
> -  'data': [ 'zlib' ] }
> +  'data': [ 'zlib', { 'name': 'zstd', 'if': 'defined(CONFIG_ZSTD)' } ] }
>  
>  ##
>  # @BlockdevCreateOptionsQcow2:

Like MultiFDCompression less value @none.

QAPI part:
Acked-by: Markus Armbruster <armbru@redhat.com>

[...]