Denis Plotnikov <dplotni...@virtuozzo.com> writes: > zstd significantly reduces cluster compression time. > It provides better compression performance maintaining > the same level of compression ratio in comparison with > zlib, which, by the moment, has been 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 <dplotni...@virtuozzo.com> [...] > diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt > index 7cf068f814..4344e858cb 100644 > --- a/docs/interop/qcow2.txt > +++ b/docs/interop/qcow2.txt > @@ -538,6 +538,9 @@ Compressed Clusters Descriptor (x = 62 - (cluster_bits - > 8)): > Another compressed cluster may map to the tail of the > final > sector used by this compressed cluster. > > + The layout of the compressed data depends on the > compression > + type used for the image (see compressed cluster layout). > + > If a cluster is unallocated, read requests shall read the data from the > backing > file (except if bit 0 in the Standard Cluster Descriptor is set). If there is > no backing file or the backing file is smaller than the image, they shall > read > @@ -790,3 +793,19 @@ In the image file the 'enabled' state is reflected by > the 'auto' flag. If this > flag is set, the software must consider the bitmap as 'enabled' and start > tracking virtual disk changes to this bitmap from the first write to the > virtual disk. If this flag is not set then the bitmap is disabled. > + > +=== Compressed cluster layout === > + > +The compressed cluster data may have a different layout depending on the > +compression type used for the image, and store specific data for the > particular > +compression type. > + > +Compressed data layout for the available compression types: > +(x = data_space_length - 1) > + > + zlib: > + Byte 0 - x: the compressed data content > + all the space provided used for compressed data > + zstd: > + Byte 0 - 3: the length of compressed data > + 4 - x: the compressed data content
Adding <http://zlib.net/> and <http://github.com/facebook/zstd> here as well wouldn't hurt, would it? > diff --git a/qapi/block-core.json b/qapi/block-core.json > index 835dd3c37f..2021e03a84 100644 > --- a/qapi/block-core.json > +++ b/qapi/block-core.json > @@ -4215,11 +4215,12 @@ > # Compression type used in qcow2 image file > # > # @zlib: zlib compression, see <http://zlib.net/> > +# @zstd: zstd compression, see <http://github.com/facebook/zstd> > # > # Since: 4.1 > ## > { 'enum': 'Qcow2CompressionType', > - 'data': [ 'zlib' ] } > + 'data': [ 'zlib', { 'name': 'zstd', 'if': 'defined(CONFIG_ZSTD)' } ] } > > ## > # @BlockdevCreateOptionsQcow2: QAPI schema Acked-by: Markus Armbruster <arm...@redhat.com>