Re: [Qemu-devel] [PATCH v2 3/3] qcow2: add zstd cluster compression

[Max Reitz]

On 04.07.19 15:09, Denis Plotnikov wrote:
> 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 <address@hidden>
> ---
>  block/qcow2.c          | 99 ++++++++++++++++++++++++++++++++++++++++++
>  configure              | 32 ++++++++++++++
>  docs/interop/qcow2.txt | 19 ++++++++
>  qapi/block-core.json   |  3 +-
>  4 files changed, 152 insertions(+), 1 deletion(-)
> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index a107f76e98..252eba636f 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c

[...]

> @@ -4092,6 +4103,84 @@ 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
> + *          a negative error code on fail
> + */
> +
> +static ssize_t qcow2_zstd_compress(void *dest, size_t dest_size,
> +                                   const void *src, size_t src_size)
> +{
> +    ssize_t ret;
> +    uint32_t *c_size = dest;
> +    /* steal some bytes to store compressed chunk size */
> +    char *d_buf = ((char *) dest) + sizeof(*c_size);
> +
> +    if (dest_size < sizeof(*c_size)) {
> +        return -ENOMEM;
> +    }
> +
> +    dest_size -= sizeof(*c_size);
> +
> +    ret = ZSTD_compress(d_buf, dest_size, src, src_size, 5);
> +
> +    if (ZSTD_isError(ret)) {
> +        if (ret == ZSTD_error_dstSize_tooSmall) {

s/ret/ZSTD_getErrorCode(ret)/

> +            return -ENOMEM;
> +        } else {
> +            return -EIO;
> +        }
> +    }
> +
> +    /* store the compressed chunk size in the very beginning of the buffer */
> +    *c_size = ret;

I think this should be stored in big endian.

> +
> +    return ret + sizeof(ret);

s/sizeof(ret)/sizeof(*c_size)/

> +}
> +
> +/*
> + * 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 fail
> + */
> +
> +static ssize_t qcow2_zstd_decompress(void *dest, size_t dest_size,
> +                                     const void *src, size_t src_size)
> +{
> +    ssize_t ret;
> +    /*
> +     * zstd decompress wants to know the exact lenght of the data

*length

> +     * for that purpose, on the compression the length is stored in
> +     * the very beginning of the compressed buffer
> +     */
> +    const uint32_t *s_size = src;
> +    const char *s_buf = ((char *) src) + sizeof(*s_size);

If you want to be strict, s/(char *)/(const char *)/.

> +
> +    ret = ZSTD_decompress(dest, dest_size, s_buf, *s_size);
> +
> +    if (ZSTD_isError(ret)) {
> +        return -EIO;
> +    }
> +
> +    return 0;
> +}
> +#endif
> +
>  #define MAX_COMPRESS_THREADS 4
>  
>  typedef ssize_t (*Qcow2CompressFunc)(void *dest, size_t dest_size,

[...]

> diff --git a/configure b/configure
> index 1c563a7027..57a80e38e7 100755
> --- a/configure
> +++ b/configure

[...]

> @@ -2374,6 +2380,29 @@ EOF
>      fi
>  fi
>  
> +#########################################
> +# zstd check
> +
> +if test "$zstd" != "no" ; then
> +    if $pkg_config --exists libzstd; then
> +        zstd_cflags=$($pkg_config --cflags libzstd)
> +        zstd_libs=$($pkg_config --libs libzstd)
> +        QEMU_CFLAGS="$zstd_cflags $QEMU_CFLAGS"
> +        LIBS="$zstd_libs $LIBS"
> +    else
> +        cat > $TMPC << EOF
> +#include <zstd.h>
> +int main(void) { ZSTD_versionNumber(); return 0; }
> +EOF
> +        if compile_prog "" "-lzstd" ; then
> +            LIBS="$LIBS -lzstd"
> +        else
> +            error_exit "zstd check failed" \
> +                "Make sure to have the zstd libs and headers installed."

(1) When the user doesn’t specify anything and doesn’t have zstd
installed, this will throw an error.  That shouldn’t be, it should just
set zstd to "no", unless zstd was explicitly "yes".

(2) All other places use feature_not_found.  I think this should, too.

> +        fi
> +    fi

You must set zstd to "yes" if it was found.

(So it is used when available, even if the user did not explicitly pass
--enable-zstd.)

> +fi
> +
>  ##########################################
>  # libseccomp check
>  
> @@ -7253,6 +7282,9 @@ fi
>  if test "$sheepdog" = "yes" ; then
>    echo "CONFIG_SHEEPDOG=y" >> $config_host_mak
>  fi
> +if test "$zstd" = "yes" ; then
> +  echo "CONFIG_ZSTD=y" >> $config_host_mak
> +fi
>  
>  if test "$tcg_interpreter" = "yes"; then
>    QEMU_INCLUDES="-iquote \$(SRC_PATH)/tcg/tci $QEMU_INCLUDES"

The status should be printed in the list of what features are enabled.

Max

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