01.04.2020 17:37, 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 <address@hidden>
QAPI part:
Acked-by: Markus Armbruster <address@hidden>
---
docs/interop/qcow2.txt | 1 +
configure | 2 +-
qapi/block-core.json | 3 +-
block/qcow2-threads.c | 163 +++++++++++++++++++++++++++++++++++++++++
block/qcow2.c | 7 ++
5 files changed, 174 insertions(+), 2 deletions(-)
diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index 640e0eca40..18a77f737e 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -209,6 +209,7 @@ version 2.
Available compression type values:
0: zlib <https://www.zlib.net/>
+ 1: zstd <http://github.com/facebook/zstd>
=== Header padding ===
diff --git a/configure b/configure
index e225a1e3ff..fdc991b010 100755
--- a/configure
+++ b/configure
@@ -1861,7 +1861,7 @@ disabled with --disable-FEATURE, default is
enabled if available:
lzfse support of lzfse compression library
(for reading lzfse-compressed dmg images)
zstd support for zstd compression library
- (for migration compression)
+ (for migration compression and qcow2 cluster
compression)
seccomp seccomp support
coroutine-pool coroutine freelist (better performance)
glusterfs GlusterFS backend
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 1522e2983f..6fbacddab2 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -4293,11 +4293,12 @@
# Compression type used in qcow2 image file
#
# @zlib: zlib compression, see <http://zlib.net/>
+# @zstd: zstd compression, see <http://github.com/facebook/zstd>
#
# Since: 5.1
##
{ 'enum': 'Qcow2CompressionType',
- 'data': [ 'zlib' ] }
+ 'data': [ 'zlib', { 'name': 'zstd', 'if': 'defined(CONFIG_ZSTD)' }
] }
##
# @BlockdevCreateOptionsQcow2:
diff --git a/block/qcow2-threads.c b/block/qcow2-threads.c
index 7dbaf53489..aa133204f0 100644
--- a/block/qcow2-threads.c
+++ b/block/qcow2-threads.c
@@ -28,6 +28,11 @@
#define ZLIB_CONST
#include <zlib.h>
+#ifdef CONFIG_ZSTD
+#include <zstd.h>
+#include <zstd_errors.h>
+#endif
+
#include "qcow2.h"
#include "block/thread-pool.h"
#include "crypto.h"
@@ -166,6 +171,154 @@ static ssize_t qcow2_zlib_decompress(void
*dest, size_t dest_size,
return ret;
}
+#ifdef CONFIG_ZSTD
+
+/*
+ * qcow2_zstd_compress()
+ *
+ * Compress @src_size bytes of data using zstd compression method
+ *
+ * @dest - destination buffer, @dest_size bytes
+ * @src - source buffer, @src_size bytes
+ *
+ * Returns: compressed size on success
+ * -ENOMEM destination buffer is not enough to store
compressed data
+ * -EIO on any other error
+ */
+static ssize_t qcow2_zstd_compress(void *dest, size_t dest_size,
+ const void *src, size_t src_size)
+{
+ ssize_t ret;
+ ZSTD_outBuffer output = { dest, dest_size, 0 };
+ ZSTD_inBuffer input = { src, src_size, 0 };
+ ZSTD_CCtx *cctx = ZSTD_createCCtx();
+
+ if (!cctx) {
+ return -EIO;
+ }
+ /*
+ * Use the zstd streamed interface for symmetry with decompression,
+ * where streaming is essential since we don't record the exact
+ * compressed size.
+ *
+ * In the loop, we try to compress all the data into one zstd
frame.
+ * ZSTD_compressStream2 potentially can finish a frame earlier
+ * than the full input data is consumed. That's why we are looping
+ * until all the input data is consumed.
+ */
+ while (input.pos < input.size) {
+ size_t zstd_ret = 0;
dead assignment
+ /*
+ * ZSTD spec: "You must continue calling ZSTD_compressStream2()
+ * with ZSTD_e_end until it returns 0, at which point you are
+ * free to start a new frame". We assume that "start a new
frame"
+ * means call ZSTD_compressStream2 in the very beginning or
when
+ * ZSTD_compressStream2 has returned with 0.
+ */
+ do {
+ zstd_ret = ZSTD_compressStream2(cctx, &output, &input,
ZSTD_e_end);
+
+ if (ZSTD_isError(zstd_ret)) {
+ ret = -EIO;
+ goto out;
+ }
+ /* Dest buffer isn't big enough to store compressed
content */
+ if (zstd_ret > output.size - output.pos) {
+ ret = -ENOMEM;
+ goto out;
+ }
+ } while (zstd_ret);
+ }
+ /* make sure we can safely return compressed buffer size with
ssize_t */
+ assert(output.pos <= SSIZE_MAX);
+ ret = output.pos;
+out:
+ ZSTD_freeCCtx(cctx);
+ return ret;
+}
+
+/*
+ * qcow2_zstd_decompress()
+ *
+ * Decompress some data (not more than @src_size bytes) to produce
exactly
+ * @dest_size bytes using zstd compression method
+ *
+ * @dest - destination buffer, @dest_size bytes
+ * @src - source buffer, @src_size bytes
+ *
+ * Returns: 0 on success
+ * -EIO on any error
+ */
+static ssize_t qcow2_zstd_decompress(void *dest, size_t dest_size,
+ const void *src, size_t src_size)
+{
+ size_t zstd_ret = 0;
+ ssize_t ret = 0;
+ ZSTD_outBuffer output = { dest, dest_size, 0 };
+ ZSTD_inBuffer input = { src, src_size, 0 };
+ ZSTD_DCtx *dctx = ZSTD_createDCtx();
+
+ if (!dctx) {
+ return -EIO;
+ }
+
+ /*
+ * The compressed stream from the input buffer may consist of more
+ * than one zstd frame. So we iterate until we get a fully
+ * uncompressed cluster.
+ * From zstd docs related to ZSTD_decompressStream:
+ * "return : 0 when a frame is completely decoded and fully
flushed"
+ * We suppose that this means: each time ZSTD_decompressStream
reads
+ * only ONE full frame and returns 0 if and only if that frame
+ * is completely decoded and flushed. Only after returning 0,
+ * ZSTD_decompressStream reads another ONE full frame.
+ */
+ while (output.pos < output.size) {
+ size_t last_in_pos = input.pos;
+ size_t last_out_pos = output.pos;
+ zstd_ret = ZSTD_decompressStream(dctx, &output, &input);
+ /*
+ * ZSTD manual doesn't explicitly state what happens,
+ * if ZSTD_decompressStream reads the frame partially.
+ * But, based on our tests, if we don't fully populate
+ * the output and have read all the frames from the input,
+ * we end up with error here.
Hmm, based on my test, that's wrong, see below. So, I'd drop the comment.
+ */
+ if (ZSTD_isError(zstd_ret)) {
+ ret = -EIO;
+ break;
+ }
+
+ /*
+ * The ZSTD manual is vague about what to do if it reads
+ * the buffer partially, and we don't want to get stuck
+ * in an infinite loop where ZSTD_decompressStream
+ * returns > 0 waiting for another input chunk. So, we add
+ * a paranoid check that on each step the loop makes some
+ * progress.
+ */
As my test shows, it's not paranoid. It's really needed. So, I'd drop
(or rewrite) the comment.
And, with dropped dead assignment and these two comments:
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
+ if (last_in_pos >= input.pos &&
+ last_out_pos >= output.pos) {
+ ret = -EIO;
+ break;
+ }
+ }
+ /*
+ * Make sure that we have the frame fully flushed here
+ * if not, we somehow managed to get uncompressed cluster
+ * greater then the cluster size, possibly because of its
+ * damage.
+ */
+ if (zstd_ret > 0) {
+ ret = -EIO;
+ }
I still don't believe that we need this check. Experiments shows that
yes, it returns 0 after each frame... But experiment is not a guarantee.
But OK, if you want, keep it.
+
+ ZSTD_freeDCtx(dctx);
+ assert(ret == 0 || ret == -EIO);
+ return ret;
+}
+#endif
+
static int qcow2_compress_pool_func(void *opaque)
{
Qcow2CompressData *data = opaque;
@@ -217,6 +370,11 @@ qcow2_co_compress(BlockDriverState *bs, void
*dest, size_t dest_size,
fn = qcow2_zlib_compress;
break;
+#ifdef CONFIG_ZSTD
+ case QCOW2_COMPRESSION_TYPE_ZSTD:
+ fn = qcow2_zstd_compress;
+ break;
+#endif
default:
abort();
}
@@ -249,6 +407,11 @@ qcow2_co_decompress(BlockDriverState *bs, void
*dest, size_t dest_size,
fn = qcow2_zlib_decompress;
break;
+#ifdef CONFIG_ZSTD
+ case QCOW2_COMPRESSION_TYPE_ZSTD:
+ fn = qcow2_zstd_decompress;
+ break;
+#endif
default:
abort();
}
diff --git a/block/qcow2.c b/block/qcow2.c
index 6cb000be19..3ae9624ba3 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1246,6 +1246,9 @@ static int
validate_compression_type(BDRVQcow2State *s, Error **errp)
{
switch (s->compression_type) {
case QCOW2_COMPRESSION_TYPE_ZLIB:
+#ifdef CONFIG_ZSTD
+ case QCOW2_COMPRESSION_TYPE_ZSTD:
+#endif
break;
default:
@@ -3478,6 +3481,10 @@ qcow2_co_create(BlockdevCreateOptions
*create_options, Error **errp)
}
switch (qcow2_opts->compression_type) {
+#ifdef CONFIG_ZSTD
+ case QCOW2_COMPRESSION_TYPE_ZSTD:
+ break;
+#endif
default:
error_setg(errp, "Unknown compression type");
goto out;
----
test:
#include <stdio.h>
#include <assert.h>
#include <zstd.h>
#include <zstd_errors.h>
int main() {
char buf1[] = "erbebewbwe";
char buf2[1000000];
char buf3[1000000];
int ret;
ZSTD_outBuffer output = { buf2, sizeof(buf2), 0 };
ZSTD_inBuffer input = { buf1, 5, 0 };
ZSTD_CCtx *cctx;
cctx = ZSTD_createCCtx();
assert(cctx);
ret = ZSTD_compressStream2(cctx, &output, &input, ZSTD_e_end);
printf("ret1: %d\n");
input = (ZSTD_inBuffer){ buf1, 5, 0 };
ret = ZSTD_compressStream2(cctx, &output, &input, ZSTD_e_end);
printf("ret2: %d\n");
ZSTD_freeCCtx(cctx);
// Now, we have written at least two frames.
printf("output.pos: %ld\n", output.pos);
ZSTD_DCtx *dctx = ZSTD_createDCtx();
input = (ZSTD_inBuffer){buf2, output.pos, 0};
output = (ZSTD_outBuffer){buf3, sizeof(buf3), 0};
ret = ZSTD_decompressStream(dctx, &output, &input);
printf("ret: %d, input.pos: %ld, output.pos: %ld\n", ret,
input.pos, output.pos);
ret = ZSTD_decompressStream(dctx, &output, &input);
printf("ret: %d, input.pos: %ld, output.pos: %ld\n", ret,
input.pos, output.pos);
ret = ZSTD_decompressStream(dctx, &output, &input);
printf("ret: %d, %d, input.pos: %ld, output.pos: %ld\n", ret,
ZSTD_isError(ret), input.pos, output.pos);
ret = ZSTD_decompressStream(dctx, &output, &input);
printf("ret: %d, %d, input.pos: %ld, output.pos: %ld\n", ret,
ZSTD_isError(ret), input.pos, output.pos);
return 0;
}
compile:
gcc -lzstd -g a.c
output:
[root@kvm zstd]# ./a.out
ret1: 1
ret2: 1
output.pos: 28
ret: 0, input.pos: 14, output.pos: 5
ret: 0, input.pos: 28, output.pos: 10
ret: 9, 0, input.pos: 28, output.pos: 10
ret: 9, 0, input.pos: 28, output.pos: 10
So, as you can see, last two decompress'es shows, that we still not
fully populate the output, nothing more in the input, and it returns
not-error... It returns 9. Interesting :)