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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190502135828.42797-3-shmuel.eiderman@oracle.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="s6sKGehxa1AM7u7r2jKzqX62fI2qScy63" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Thu, 23 May 2019 14:01:52 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 X-Content-Filtered-By: Mailman/MimeDel 2.1.21 Subject: Re: [Qemu-devel] [PATCH v2 2/3] qemu-img: rebase: Reduce reads on in-chain rebase X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: sagi.amit@oracle.com, arbel.moshe@oracle.com, liran.alon@oracle.com, eyal.moscovici@oracle.com, karl.heubaum@oracle.com 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) --s6sKGehxa1AM7u7r2jKzqX62fI2qScy63 From: Max Reitz To: Sam Eiderman , kwolf@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: eyal.moscovici@oracle.com, sagi.amit@oracle.com, karl.heubaum@oracle.com, liran.alon@oracle.com, arbel.moshe@oracle.com Message-ID: Subject: Re: [PATCH v2 2/3] qemu-img: rebase: Reduce reads on in-chain rebase References: <20190502085029.30776-1-shmuel.eiderman@oracle.com> <20190502135828.42797-1-shmuel.eiderman@oracle.com> <20190502135828.42797-3-shmuel.eiderman@oracle.com> In-Reply-To: <20190502135828.42797-3-shmuel.eiderman@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 02.05.19 15:58, Sam Eiderman wrote: > In the following case: >=20 > (base) A <- B <- C (tip) >=20 > when running: >=20 > qemu-img rebase -b A C >=20 > QEMU would read all sectors not allocated in the file being rebased (C)= > and compare them to the new base image (A), regardless of whether they > were changed or even allocated anywhere along the chain between the new= > base and the top image (B). This causes many unneeded reads when > rebasing an image which represents a small diff of a large disk, as it > would read most of the disk's sectors. >=20 > Instead, use bdrv_is_allocated_above() to reduce the number of > unnecessary reads. >=20 > Reviewed-by: Karl Heubaum > Signed-off-by: Sam Eiderman > Signed-off-by: Eyal Moscovici > --- > qemu-img.c | 25 ++++++++++++++++++++++++- > 1 file changed, 24 insertions(+), 1 deletion(-) >=20 > diff --git a/qemu-img.c b/qemu-img.c > index d9b609b3f0..7f20858cb9 100644 > --- a/qemu-img.c > +++ b/qemu-img.c [...] > @@ -3422,6 +3428,23 @@ static int img_rebase(int argc, char **argv) > continue; > } > =20 > + if (prefix_chain_bs) { > + /* > + * If cluster wasn't changed since prefix_chain, we do= n't need > + * to take action > + */ > + ret =3D bdrv_is_allocated_above(bs, prefix_chain_bs, > + offset, n, &n); This will always return true because it definitely is allocated in @bs, or we wouldn=E2=80=99t be here. (We just checked that with bdrv_is_allocated().) I think @top should be backing_bs(bs). Max > + if (ret < 0) { > + error_report("error while reading image metadata: = %s", > + strerror(-ret)); > + goto out; > + } > + if (!ret) { > + continue; > + } > + } > + > /* > * Read old and new backing file and take into considerati= on that > * backing files may be smaller than the COW image. >=20 --s6sKGehxa1AM7u7r2jKzqX62fI2qScy63 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAlzmp8wACgkQ9AfbAGHV z0DC4AgArkNz2w/pi46i1kT3xZfnoFRLrPpZZ91hG/6HEurEb1/XN12F0/PeNRpZ 0hnL2n5hVnrudqZPxk0sJ58s0utVBOaR0JKdA+x9LIHKNnLDx2zsMLEhp+6DneiN mg+nU8w+yBW0WM1dwr7st1gTmyhDWibTHuVOYXhE+t2lD/WpX0ymNTTp8VJrQ+rc kmJrv/1IS7VwUkGLlGpA0W34MexTOXs8o4cyyKYGGQBAbz6RMRU5g+dCNdKvU1WG 7orAqWUfMx4dZmUAYf6/66wiNAjCLq9+ufM61miG0GwzAGEzpvTbuLKjuuc8QNME LRlMyS7E1EmV7HKAKfLDuhEUqBXD2A== =E2Q0 -----END PGP SIGNATURE----- --s6sKGehxa1AM7u7r2jKzqX62fI2qScy63--