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Tue, 28 Apr 2020 06:16:31 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-112-143.ams2.redhat.com [10.36.112.143]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4A6C55D715; Tue, 28 Apr 2020 06:16:29 +0000 (UTC) Subject: Re: [PATCH v20 3/4] qcow2: add zstd cluster compression To: Denis Plotnikov , qemu-devel@nongnu.org References: <20200421081117.7595-1-dplotnikov@virtuozzo.com> <20200421081117.7595-4-dplotnikov@virtuozzo.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <6f9049f9-4b2a-796d-d3f7-dbd9dbe720cc@redhat.com> Date: Tue, 28 Apr 2020 08:16:27 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="jQS9u8r28eRviwDeKkH9nz0SiW06A5AzN" Received-SPF: pass client-ip=205.139.110.61; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/28 02:06:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, berto@igalia.com, qemu-block@nongnu.org, armbru@redhat.com, den@openvz.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --jQS9u8r28eRviwDeKkH9nz0SiW06A5AzN Content-Type: multipart/mixed; boundary="RWSaHtZ1SFSlQmsOj2j78bH06XYk13aL0" --RWSaHtZ1SFSlQmsOj2j78bH06XYk13aL0 Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 27.04.20 21:26, Denis Plotnikov wrote: >=20 >=20 > On 27.04.2020 15:35, Max Reitz wrote: >> On 21.04.20 10:11, 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: >>> =A0=A0 time ./qemu-img convert -O qcow2 -c -o compression_type=3D[zlib|= zstd] >>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 src.img [zlib|zs= td]_compressed.img >>> decompress cmd >>> =A0=A0 time ./qemu-img convert -O qcow2 >>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 [zlib|zstd]_comp= ressed.img uncompressed.img >>> >>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 compression=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0 decompression >>> =A0=A0=A0=A0=A0=A0=A0=A0=A0 zlib=A0=A0=A0=A0=A0=A0 zstd=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0 zlib=A0=A0=A0=A0=A0=A0=A0=A0 zstd >>> ------------------------------------------------------------ >>> real=A0=A0=A0=A0 65.5=A0=A0=A0=A0=A0=A0 16.3 (-75 %)=A0=A0=A0 1.9=A0=A0= =A0=A0=A0=A0=A0=A0=A0 1.6 (-16 %) >>> user=A0=A0=A0=A0 65.0=A0=A0=A0=A0=A0=A0 15.8=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0 5.3=A0=A0=A0=A0=A0=A0=A0=A0=A0 2.5 >>> sys=A0=A0=A0=A0=A0=A0 3.3=A0=A0=A0=A0=A0=A0=A0 0.2=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0 2.0=A0=A0=A0=A0=A0=A0=A0=A0=A0 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 >>> Reviewed-by: Vladimir Sementsov-Ogievskiy >>> Reviewed-by: Alberto Garcia >>> QAPI part: >>> Acked-by: Markus Armbruster >>> --- >>> =A0 docs/interop/qcow2.txt |=A0=A0 1 + >>> =A0 configure=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 |=A0=A0 2 +- >>> =A0 qapi/block-core.json=A0=A0 |=A0=A0 3 +- >>> =A0 block/qcow2-threads.c=A0 | 157 ++++++++++++++++++++++++++++++++++++= +++++ >>> =A0 block/qcow2.c=A0=A0=A0=A0=A0=A0=A0=A0=A0 |=A0=A0 7 ++ >>> =A0 5 files changed, 168 insertions(+), 2 deletions(-) >> [...] >> >>> diff --git a/block/qcow2-threads.c b/block/qcow2-threads.c >>> index 7dbaf53489..0525718704 100644 >>> --- a/block/qcow2-threads.c >>> +++ b/block/qcow2-threads.c >>> @@ -28,6 +28,11 @@ >>> =A0 #define ZLIB_CONST >>> =A0 #include >>> =A0 +#ifdef CONFIG_ZSTD >>> +#include >>> +#include >>> +#endif >>> + >>> =A0 #include "qcow2.h" >>> =A0 #include "block/thread-pool.h" >>> =A0 #include "crypto.h" >>> @@ -166,6 +171,148 @@ static ssize_t qcow2_zlib_decompress(void >>> *dest, size_t dest_size, >>> =A0=A0=A0=A0=A0 return ret; >>> =A0 } >>> =A0 +#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 >>> + *=A0=A0=A0=A0=A0=A0=A0=A0=A0 -ENOMEM destination buffer is not enough= to store >>> compressed data >>> + *=A0=A0=A0=A0=A0=A0=A0=A0=A0 -EIO=A0=A0=A0 on any other error >>> + */ >>> +static ssize_t qcow2_zstd_compress(void *dest, size_t dest_size, >>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 const void *src, size_t src_size) >>> +{ >>> +=A0=A0=A0 ssize_t ret; >>> +=A0=A0=A0 ZSTD_outBuffer output =3D { dest, dest_size, 0 }; >>> +=A0=A0=A0 ZSTD_inBuffer input =3D { src, src_size, 0 }; >> Minor style note: I think it=92d be nicer to use designated initializers >> here. >> >>> +=A0=A0=A0 ZSTD_CCtx *cctx =3D ZSTD_createCCtx(); >>> + >>> +=A0=A0=A0 if (!cctx) { >>> +=A0=A0=A0=A0=A0=A0=A0 return -EIO; >>> +=A0=A0=A0 } >>> +=A0=A0=A0 /* >>> +=A0=A0=A0=A0 * Use the zstd streamed interface for symmetry with decom= pression, >>> +=A0=A0=A0=A0 * where streaming is essential since we don't record the = exact >>> +=A0=A0=A0=A0 * compressed size. >>> +=A0=A0=A0=A0 * >>> +=A0=A0=A0=A0 * In the loop, we try to compress all the data into one z= std >>> frame. >>> +=A0=A0=A0=A0 * ZSTD_compressStream2 potentially can finish a frame ear= lier >>> +=A0=A0=A0=A0 * than the full input data is consumed. That's why we are= looping >>> +=A0=A0=A0=A0 * until all the input data is consumed. >>> +=A0=A0=A0=A0 */ >>> +=A0=A0=A0 while (input.pos < input.size) { >>> +=A0=A0=A0=A0=A0=A0=A0 size_t zstd_ret; >>> +=A0=A0=A0=A0=A0=A0=A0 /* >>> +=A0=A0=A0=A0=A0=A0=A0=A0 * ZSTD spec: "You must continue calling ZSTD_= compressStream2() >>> +=A0=A0=A0=A0=A0=A0=A0=A0 * with ZSTD_e_end until it returns 0, at whic= h point you are >>> +=A0=A0=A0=A0=A0=A0=A0=A0 * free to start a new frame". We assume that = "start a new >>> frame" >>> +=A0=A0=A0=A0=A0=A0=A0=A0 * means call ZSTD_compressStream2 in the very= beginning or >>> when >>> +=A0=A0=A0=A0=A0=A0=A0=A0 * ZSTD_compressStream2 has returned with 0. >>> +=A0=A0=A0=A0=A0=A0=A0=A0 */ >>> +=A0=A0=A0=A0=A0=A0=A0 do { >>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 zstd_ret =3D ZSTD_compressStream2(cc= tx, &output, &input, >>> ZSTD_e_end); >> The spec makes it sound to me like ZSTD_e_end will always complete in a >> single call if there=92s enough space in the output buffer.=A0 So the on= ly >> team we have to loop would be when there isn=92t enough space anyway: >> >> It says this about ZSTD_e_end: >>> flush operation is the same, and follows same rules as calling >>> ZSTD_compressStream2() with ZSTD_e_flush. >> Those rules being: >>> Note that, if `output->size` is too small, a single invocation with >>> ZSTD_e_flush might not be enough (return code > 0). >> So it seems like it will only return a value > 0 if the output buffer is >> definitely too small. >> >> The spec also notes that the return value is greater than 0 if: >>>> 0 if some data still present within internal buffer (the value is >>> minimal estimation of remaining size), >> So it=92s a minimum estimate.=A0 That=92s another point that heavily imp= lies >> to me that if the return value were less than what=92s left in the buffe= r, >> the function wouldn=92t return but still try to write it out, until it >> realizes that there isn=92t enough space in the output buffer, and then >> return a value that exceeds the remaining output buffer size. >> >> (Because if the function just played it safe, I would expect it to >> return a maximum estimate.) >> >> >> OTOH, if it were actually possible for ZSTD_e_end to finish a frame >> earlier than the end of the input, I think it would make more sense to >> use ZSTD_e_continue until the input is done and then finish with >> ZSTD_e_end, like the spec seems to propose.=A0 That way, we=92d always e= nd >> up with a single frame to make decompression simpler (and I think it >> would also make more sense overall). >> >> >> But anyway.=A0 From how I understand the spec, this code simply always >> ends up creating a single frame or erroring out, without looping ever. >> So it isn=92t exactly wrong, it just seems overly complicated.=A0 (Again= , >> assuming I understand the spec correctly.=A0 Which seems like a tough >> thing to assume, because the spec is not exactly obvious to read...) >> >> (Running some quick tests by converting some images with zstd >> compression seems to confirm that whenever ZSTD_compressStream2() >> returns, either zstd_ret > output.size - output.pos, or zstd_ret =3D=3D = 0 >> and input.pos =3D=3D input.size.=A0 So none of the loops ever loop.) >> >> Max >=20 > So, what should we do? >=20 > 1. Rely on the test that there's no need for the loop: > =A0=A0 * make one ZSTD_compressStream2() call > =A0=A0 * make sure it returned with zstd_ret =3D=3D 0 and > =A0=A0=A0=A0 input.pos =3D=3D input.size. > =A0=A0=A0=A0 if so, return with the size > =A0=A0 * if not, check that zstd_ret > output.size - output.pos > =A0=A0=A0=A0 if so, return with -ENOMEM > =A0=A0 * if none above return with -EIO >=20 > =A0=A0 This should cover the majority of the compressing cases According to how I interpret the spec, =93none of the above=94 should never happen except for ZSTD_isError(zstd_ret), so this should cover all compressing cases, actually. > 2. Leave the loop as is, because of the documentation: > =A0=A0 "You *must* continue calling ZSTD_compressStream2() with ZSTD_e_en= d > until it returns 0, > =A0=A0=A0 at which point you are free to start a new frame." As far as I can see, the return value is always 0 or greater than the remaining buffer space, so this will always be satisfied even without a loop. (We will always have one of three cases: (1) Success and all input has been consumed, (2) ZSTD_isError(zstd_ret), so we return -EIO, (3) zstd_ret > output.size - output.pos, so we return -ENOMEM. I interpret the =93You *must* continue until it returns 0=94 as =93If there= is no sufficient space in the output buffer, this function will return a value greater than 0 indicating how much space is at least still required. The caller is free to supply a greater output buffer for the next call (by supplying a different ZSTD_outBuffer structure), and then we=92ll try again.=94 (I.e., retrying with the same ZSTD_outBuffer will make the function return immediately because it knows that it=92s insufficient.) 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