On 29.04.2020 13:24, Max Reitz wrote:
On 28.04.20 22:00, Denis Plotnikov wrote:
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 <dplotni...@virtuozzo.com>
QAPI part:
Acked-by: Markus Armbruster <arm...@redhat.com>
---
docs/interop/qcow2.txt | 1 +
configure | 2 +-
qapi/block-core.json | 3 +-
block/qcow2-threads.c | 169 +++++++++++++++++++++++++++++++++++++++++
block/qcow2.c | 7 ++
slirp | 2 +-
6 files changed, 181 insertions(+), 3 deletions(-)
[...]
diff --git a/block/qcow2-threads.c b/block/qcow2-threads.c
index 7dbaf53489..a0b12e1b15 100644
--- a/block/qcow2-threads.c
+++ b/block/qcow2-threads.c
[...]
+static ssize_t qcow2_zstd_decompress(void *dest, size_t dest_size,
+ const void *src, size_t src_size)
+{
[...]
+ /*
+ * The compressed stream from the input buffer may consist of more
+ * than one zstd frame.
Can it?
Potentially, it can, if another implemention of qcow2 saves a couple of
frames for some reason.
Denis
Max
